Patent Application
20250017036
One embodiment of the present invention relates to a light-emitting device.
Note that one embodiment of the present invention is not limited to the above technical field. Examples of the technical field of one embodiment of the present invention include a semiconductor device, a display apparatus, a light-emitting apparatus, a power storage device, a memory device, an electronic device, a lighting device, an input device (e.g., a touch sensor), an input/output device (e.g., a touch panel), driving methods thereof, and manufacturing methods thereof.
Display apparatuses are being developed into a variety of applications these days. For example, a television device for home use (also referred to as TV or television receiver), digital signage, and a public information display (PID) are being developed as large-sized display apparatuses, and a smartphone and a tablet terminal each provided with a touch panel are being developed as small-sized display apparatuses.
At the same time, an increase in the resolution of display apparatus is also required. For example, devices for virtual reality (VR), augmented reality (AR), substitutional reality (SR), or mixed reality (MR) are given as devices requiring high-resolution display apparatuses and are being developed actively.
Development is actively conducted on light-emitting devices (also referred to as light-emitting elements) as display elements used in display apparatuses. Light-emitting devices utilizing electroluminescence (hereinafter referred to as EL; such devices are also referred to as EL devices or EL elements), particularly organic EL devices that mainly use organic compounds, are suitable for display apparatuses because of having features such as ease of reduction in thickness and weight, high-speed response to input signals, and driving with a constant DC voltage power source.
In order to obtain a higher-resolution light-emitting apparatus using an organic EL device, patterning an organic layer by a photolithography technique using a photoresist or the like, instead of an evaporation method using a metal mask, has been studied. By using the photolithography technique, a high-resolution display apparatus in which the distance between EL layers is several micrometers can be obtained (see Patent Document 1, for example).
It has been known that EL layers in an organic EL device exposed to atmospheric components such as water and oxygen have affected initial characteristics or reliability, and thus it has been common knowledge that the EL layers are treated in a near-vacuum atmosphere. In particular, an electron-injection layer or an intermediate layer of a tandem organic EL device, which includes a material having a donor property typified by an alkali metal, an alkaline earth metal, or a compound thereof highly reactive with water or oxygen, rapidly deteriorates and loses the function as the intermediate layer when the surface of the EL layer is exposed to the air.
However, processing steps with the aforementioned photolithography technique inevitably expose the surface of the EL layer to the air. Favorable characteristics have been hard to obtain from organic EL devices manufactured through processing with a photolithography technique.
In view of the above, an object of one embodiment of the present invention is to provide a novel light-emitting device having a tandem structure. An object of another embodiment of the present invention is to provide a highly efficient light-emitting device having a tandem structure. An object of another embodiment of the present invention is to provide a highly reliable light-emitting device having a tandem structure. An object of another embodiment of the present invention is to provide a highly efficient and highly reliable light-emitting device having a tandem structure.
An object of another embodiment of the present invention is to provide a novel light-emitting device having a tandem structure and manufactured through a photolithography process. An object of another embodiment of the present invention is to provide a highly efficient light-emitting device having a tandem structure and manufactured through a photolithography process. An object of another embodiment of the present invention is to provide a highly reliable light-emitting device having a tandem structure and manufactured through a photolithography process. An object of another embodiment of the present invention is to provide a high-emission-efficiency and highly reliable light-emitting device having a tandem structure and manufactured through a photolithography process.
An object of another embodiment of the present invention is to provide a novel light-emitting device that has a tandem structure and can be used in a high-resolution display apparatus. An object of another embodiment of the present invention is to provide a highly efficient light-emitting device that has a tandem structure and can be used in a high-resolution display apparatus. An object of another embodiment of the present invention is to provide a highly reliable light-emitting device that has a tandem structure and can be used in a high-resolution display apparatus. An object of another embodiment of the present invention is to provide a high-emission-efficiency and highly reliable light-emitting device that has a tandem structure and can be used in a high-resolution display apparatus.
An object of another embodiment of the present invention is to provide a highly reliable display apparatus. An object of another embodiment of the present invention is to provide a high-resolution display apparatus. An object of another embodiment of the present invention is to provide a highly reliable and high-resolution display apparatus.
Note that the description of these objects does not preclude the existence of other objects. One embodiment of the present invention does not necessarily achieve all of these objects. Other objects can be derived from the description of the specification, the drawings, the claims, and the like.
One embodiment of the present invention is a light-emitting device of a plurality of light-emitting devices included in a light-emitting device group. The light-emitting device group includes a first electrode group formed over the same insulating surface, a second electrode facing the first electrode group, and a first layer group positioned between the first electrode group and the second electrode. The first electrode group includes a plurality of first electrodes independent for each of the plurality of light-emitting devices. The first layer group includes a plurality of first layers independent for each of the plurality of light-emitting devices. The second electrode is a continuous conductive layer shared by the plurality of light-emitting devices. The light-emitting device includes one of the first electrodes included in the first electrode group, the second electrode, and one of the first layers included in the first layer group. The second electrode and the first layer overlap with the first electrode. The first layer includes a first light-emitting layer, a second light-emitting layer, and an intermediate layer positioned between the first light-emitting layer and the second light-emitting layer. The intermediate layer includes a first region including a metal oxide and a first organic compound. The first organic compound is an organic compound having a phenanthroline ring with an electron-donating group. The distance between the first layer included in the light-emitting device and the first layer included in another light-emitting device adjacent to the light-emitting device is greater than or equal to 2 μm and less than or equal to 5 μm.
Another embodiment of the present invention is the light-emitting device with the above structure, in which the metal oxide is an oxide including any of Group 1, Group 2, Group 3, Group 11, Group 12, and Group 13 elements. Another embodiment of the present invention is the light-emitting device with the above structure, in which the metal oxide is an oxide of any of lithium, magnesium, calcium, silver, zinc, and indium.
Another embodiment of the present invention is the light-emitting device with any of the above structures, in which when the threshold value of electron density distribution in atomic units is 0.0004 e/a03, the minimum value of the electrostatic potential of the first organic compound is smaller than or equal to −0.085 Eh.
Another embodiment of the present invention is the light-emitting device with any of the above structures, in which the phenanthroline ring is a 1,10-phenanthroline ring and the electron-donating group is at at least one of a 4-position and a 7-position of the 1,10-phenanthroline ring.
Another embodiment of the present invention is the light-emitting device with any of the above structures, in which the electron-donating group is any one or more of an alkyl group, an alkoxy group, an aryloxy group, an alkylamino group, an arylamino group, and a heterocyclic amino group.
Another embodiment of the present invention is the light-emitting device with any of the above structures, in which the phenanthroline ring is a 1,10-phenanthroline ring, the electron-donating group is at at least one of a 4-position and a 7-position of the 1,10-phenanthroline ring, and the electron-donating group is any one or more of an alkyl group, an alkoxy group, an aryloxy group, an alkylamino group, an arylamino group, and a heterocyclic amino group.
Another embodiment of the present invention is the light-emitting device with any of the above structures, in which an acid dissociation constant pKa of the first organic compound is higher than or equal to 8.
Another embodiment of the present invention is the light-emitting device with any of the above structures, in which the first region further includes a second organic compound.
Another embodiment of the present invention is the light-emitting device with any of the above structures, in which the second organic compound includes a π-electron deficient heteroaromatic ring.
Another embodiment of the present invention is the light-emitting device with any of the above structures, in which a glass transition temperature of the second organic compound is higher than or equal to 100° C.
Another embodiment of the present invention is the light-emitting device with any of the above structures, in which the metal oxide and the first organic compound are mixed in the first region.
Another embodiment of the present invention is the light-emitting device with any of the above structures, in which a layer including the metal oxide and a layer including the first organic compound are stacked in the first region.
Another embodiment of the present invention is the light-emitting device with any of the above structures, in which the spin density of the first region measured by an electron spin resonance method is higher than or equal to 5×1016 spins/cm3.
Another embodiment of the present invention is the light-emitting device with any of the above structures, in which the intermediate layer includes a second region. The second region is positioned between the first region and the second electrode. The second region includes a third organic compound having a hole-transport property and a first substance having an acceptor property with respect to the third organic compound. Another embodiment of the present invention is the light-emitting device with any of the above structures, in which the second region includes the third organic compound having a hole-transport property and an organic compound having four or more halogen groups, four or more cyano groups, or a combination of a halogen group and a cyano group the number of which is four or more. Another embodiment of the present invention is the light-emitting device with any of the above structures, in which the second region includes the third organic compound having a hole-transport property and a metal oxide different from the metal oxide included in the first region.
Another embodiment of the present invention is the light-emitting device with any of the above structures, in which a third region including a second substance is provided between the first region and the second region.
Another embodiment of the present invention is the light-emitting device with any of the above structures, in which the spin density of the second region measured by an electron spin resonance method is higher than or equal to 1×1017 spins/cm3.
Another embodiment of the present invention is the light-emitting device with any of the above structures, in which the light-emitting device includes a second layer. The second layer is shared by the plurality of light-emitting devices and is positioned between the first layer and the second electrode.
Another embodiment of the present invention is a display apparatus including any of the above light-emitting devices.
Another embodiment of the present invention is a display module including the above-described display apparatus and at least one of a connector and an integrated circuit.
Another embodiment of the present invention is an electronic device including the above-described display module and at least one of a housing, a battery, a camera, a speaker, and a microphone.
With one embodiment of the present invention, a novel light-emitting device having a tandem structure can be provided. With another embodiment of the present invention, a highly efficient light-emitting device having a tandem structure can be provided. With another embodiment of the present invention, a highly reliable light-emitting device having a tandem structure can be provided. With another embodiment of the present invention, a highly efficient and highly reliable light-emitting device having a tandem structure can be provided.
With another embodiment of the present invention, a novel light-emitting device having a tandem structure and manufactured through a photolithography process can be provided. With another embodiment of the present invention, a highly efficient light-emitting device having a tandem structure and manufactured through a photolithography process can be provided. With another embodiment of the present invention, a highly reliable light-emitting device having a tandem structure and manufactured through a photolithography process can be provided. With another embodiment of the present invention, a high-emission-efficiency and highly reliable light-emitting device having a tandem structure and manufactured through a photolithography process can be provided.
With another embodiment of the present invention, a novel light-emitting device that has a tandem structure and can be used in a high-resolution display apparatus can be provided. With another embodiment of the present invention, a highly efficient light-emitting device that has a tandem structure and can be used in a high-resolution display apparatus can be provided. With another embodiment of the present invention, a highly reliable light-emitting device that has a tandem structure and can be used in a high-resolution display apparatus can be provided. With another embodiment of the present invention, a high-emission-efficiency and highly reliable light-emitting device that has a tandem structure and can be used in a high-resolution display apparatus can be provided.
With another embodiment of the present invention, a highly reliable display apparatus can be provided. With another embodiment of the present invention, a high-resolution display apparatus can be provided. With another embodiment of the present invention, a highly reliable and high-resolution display apparatus can be provided.
Note that the description of these effects does not preclude the existence of other effects. One embodiment of the present invention does not necessarily have all of these effects. Other effects can be derived from the description of the specification, the drawings, the claims, and the like.
In the accompanying drawings:
Embodiments will be described in detail with reference to the drawings. Note that the embodiments of the present invention are not limited to the following description, and it will be readily appreciated by those skilled in the art that modes and details of the present invention can be modified in various ways without departing from the spirit and scope of the present invention. Therefore, the present invention should not be construed as being limited to the description in the following embodiments.
In this specification and the like, a device formed using a metal mask or a fine metal mask (FMM) is sometimes referred to as a device having a metal mask (MM) structure. In this specification and the like, a device formed without using a metal mask or an FMM is sometimes referred to as a device having a metal maskless (MML) structure.
A tandem organic EL device which includes a plurality of light-emitting units between a pair of electrodes and an intermediate layer that generates carriers between the plurality of light-emitting units can have higher current efficiency than a normal organic EL device which includes only one light-emitting unit between electrodes.
The intermediate layer in the tandem organic EL device includes a carrier-generation layer (CGL). The CGL refers to a layer where electrons and holes are generated by charge separation caused by application of voltage.
Stacking and using, as the CGL, a layer including a material having a hole-transport property and a material having an electron-acceptor property with respect to the material having a hole-transport property (P-type CGL) and a layer including a material having an electron-transport property and a material having a donor property with respect to the material having an electron-transport property (N-type CGL) facilitate injection of holes or electrons to each light-emitting unit and are preferable to lower the driving voltage.
This is because injecting holes generated in the P-type CGL to a hole-transport layer of the light-emitting unit on the cathode side through the material having a hole-transport property included in the P-type CGL and injecting electrons generated in the N-type CGL to an electron-transport layer of the light-emitting unit on the anode side through the material having an electron-transport property included in the N-type CGL can lower a carrier injection barrier.
As a method for forming an organic compound film in a predetermined shape at a predetermined position, a vacuum evaporation method with a metal mask (mask vapor deposition) is widely used. However, density and resolution have been recently increasing; thus, increasing resolution in the mask vapor deposition is reaching its limit due to problems typified by a problem of the degree of positioning precision and a problem of the arrangement interval of the substrate and the mask.
By contrast, a photolithography technique is a processing method that enables a finer pattern than the mask vapor deposition. Moreover, since the photolithography technique achieves large-area processing easily, processing of an organic compound film with the photolithography technique instead of the mask vapor deposition is being researched. However, processing of an organic compound film with the photolithography technique has a problem specific to an organic EL device.
It is known that when an organic EL device is exposed to atmospheric components such as water and oxygen, initial characteristics and reliability are affected, and thus it has been common knowledge that the organic EL device is treated in a near-vacuum atmosphere.
In particular, attention is to be paid to an electron-injection layer in an organic EL device and an N-type CGL of an intermediate layer used in a tandem organic EL device. The electron-injection layer and the N-type CGL each include, as a donor for generating electrons, a material having a donor property with respect to an electron-transport material, typically an alkali metal, an alkaline earth metal, or a compound thereof (hereinafter also referred to as an alkali metal compound or the like). The alkali metal compound or the like is highly reactive with water or oxygen and thus rapidly deteriorates not only when directly exposed to the air but also when exposed to the air through a plurality of organic compound layers. As a result, the function as the electron-injection layer and the intermediate layer is lost.
However, processing steps with the aforementioned photolithography technique inevitably expose the surface of the EL layer to the air. The processing with the photolithography technique therefore causes a significant deterioration of the electron-injection properties of an electron-injection layer and an intermediate layer using an alkali metal compound or the like. Thus, an organic EL device that includes one or both of an electron-injection layer and an intermediate layer using an alkali metal compound or the like and is processed by a photolithography technique has increased driving voltage and is hard to obtain favorable characteristics.
The electron-injection layer can be formed after the processing because of the structure of an EL layer in the organic EL device (in the case of a forward-stacked device), and thus, can avoid the influence of the processing with a photolithography technique.
Meanwhile, in a tandem organic EL device, when a light-emitting layer in a light-emitting unit on the cathode side is processed by a photolithography technique, an intermediate layer of the light-emitting unit that is in contact with the anode side is inevitably exposed to processing. For this reason, a tandem organic EL device including an intermediate layer using an alkali metal compound or the like has difficulty in obtaining favorable characteristics while being processed by a photolithography technique.
If high reactivity of an alkali metal compound or the like used for an N-type CGL of an intermediate layer causes deterioration due to high reaction in an air exposure step or the like, the use of a substance with low reactivity instead of the alkali metal compound or the like may probably inhibit an increase in driving voltage even through processing with a photolithography technique.
Most of metal oxides (excluding an oxide of an alkali metal) are more stable than the alkali metal compound or the like and thus can be easily treated. In addition, the stable metal oxides relatively hardly deteriorate even when exposed to the air. However, even when the metal oxide is used instead of the alkali metal compound or the like in an N-type CGL of an intermediate layer of a conventional light-emitting device, characteristics comparable to those offered by the alkali metal compound or the like are hard to obtain because of the stability of the metal oxide. That is, it has been difficult to obtain a tandem organic EL device with characteristics that could withstand practical use.
Here, the present inventors have found that a tandem organic EL device with favorable characteristics can be obtained even through a photolithography process involving exposure to the air of an EL layer by using a layer including a metal oxide and an organic compound having a phenanthroline ring with an electron-donating group instead of an N-type CGL of an intermediate layer.
That is, when a region (a first region) including a metal oxide and an organic compound (a first organic compound) having a phenanthroline ring with an electron-donating group is provided instead of an N-type CGL of an intermediate layer, an organic EL device with favorable characteristics as a tandem organic EL device can be obtained even through a photolithography process involving exposure to the air of an EL layer.
The reason for the above is as follows: in the first organic compound, a phenanthroline ring that is likely to interact with a metal or the like has an electron-donating group; thus, the electron density of the phenanthroline ring increases and interaction even with a stable metal oxide can be caused so that the donor property to an adjacent electron-transport material can be exhibited.
The metal oxide and the first organic compound form a donor level (a singly occupied molecular orbital (SOMO) level or a highest occupied molecular orbital (HOMO) level) when interacting with each other. This reduces the electron-injection barrier to an electron-transport layer, whereby electrons generated in an intermediate layer can be smoothly injected and transported to the electron-transport layer.
Since the metal oxide is stable as described above, even when the fabrication process includes processing with a photolithography technique involving exposure to the air of an EL layer, the organic EL device of one embodiment of the present invention can have characteristics comparable or superior to those of an organic EL device fabricated by what is called a continuous vacuum process without being exposed to the air.
By using the metal oxide and the first organic compound, the intermediate layer can have resistance to oxygen and water in the air and water and a chemical solution used during the lithography process. Thus, one embodiment of the present invention can provide an organic EL device having high moisture resistance, high water resistance, high oxygen resistance, high chemical resistance, a low driving voltage, and high emission efficiency.
The region (the first region) including the metal oxide and the organic compound (the first organic compound) having a phenanthroline ring with an electron-donating group can have either a structure including a mixture layer of the metal oxide and the first organic compound or a stacked structure of a layer including the metal oxide and a layer including the first organic compound. In the case where the first region has a stacked structure of a layer including the metal oxide and a layer including the first organic compound, it is preferable that the layer including the metal oxide and the layer including the first organic compound be stacked on the cathode side and the anode side, respectively, to be in contact with each other and the layer including the first organic compound be in contact with a light-emitting unit on the anode side.
In the case where the first region is a mixture layer of the metal oxide and the first organic compound, a tandem organic EL device with favorable characteristics can be obtained even when it is fabricated by a continuous vacuum process or a process involving exposure to the air. The mixture layer can have a smaller number of layers than the stacked structure, and thus is highly productive and easy to mass produce.
In the case where the first region has a stacked structure of a layer including the metal oxide and a layer including the first organic compound, a light-emitting device fabricated through exposure to the air of an EL layer can have significantly improved characteristics in some cases as compared with a light-emitting device fabricated by a continuous vacuum process. This means that the exposure to the air of an EL layer improves the characteristics, which can be regarded as an opposite effect of the conventional theory.
Unlike other metal oxides, an oxide of an alkali metal or an alkaline earth metal such as lithium oxide (Li2O) exhibits favorable characteristics when used for an N-type CGL of a tandem organic EL device that is fabricated by a continuous vacuum process. Meanwhile, in the case where a tandem organic EL device is fabricated through a photolithography process involving exposure to the air of an EL layer, the tandem organic EL device has largely increased driving voltage as compared with an organic EL device fabricated by a continuous vacuum process even when an oxide of an alkali metal or an alkaline earth metal is used for an N-type CGL. This is probably because, as described above, the oxide of an alkali metal or an alkaline earth metal deteriorates due to the exposure to the air and the donor property decreases.
In one embodiment of the present invention, an oxide of an alkali metal or an alkaline earth metal such as lithium oxide (Li2O) and an organic compound (the first organic compound) having a phenanthroline ring with an electron-donating group are used for an intermediate layer; thus, even when fabricated through a photolithography process involving exposure to the air, an organic EL device can exhibit favorable characteristics comparable to those of an organic EL device fabricated by a continuous vacuum process.
The reason for the above is as follows: in the first region, the oxide of an alkali metal or an alkaline earth metal and the first organic compound having a phenanthroline ring with an electron-donating group interact with each other to form a donor level (SOMO level or HOMO level), which has a high energy level; accordingly, the electron-injection barrier from the intermediate layer to the electron-transport layer is reduced and electrons generated in the intermediate layer can be smoothly injected and transported to the electron-transport layer. It is thus possible to obtain a tandem organic EL device that has favorable characteristics and an increase in driving voltage suppressed even when exposed to the air.
As described above, by using the first region including a metal oxide and an organic compound (the first organic compound) having a phenanthroline ring with an electron-donating group instead of the N-type CGL, the tandem organic EL device of one embodiment of the present invention can have favorable characteristics even through a process involving exposure to the air of an EL layer. That is, the use of the structure of one embodiment of the present invention offers a tandem organic EL device with favorable characteristics, which is fabricated by a photolithography technique involving exposure to the air of an EL layer. As a result, a display device with extremely high resolution and favorable characteristics can be provided.
Note that the first region may be formed using a metal alone instead of a metal oxide, and the metal alone may be oxidized during or after formation of the first region, an intermediate layer, or a light-emitting unit so that the first region includes a metal oxide. For example, the metal oxide can be obtained by oxidizing the metal alone in an air exposure step or a processing step (e.g., heat treatment) in an atmosphere containing oxygen such as the air during the fabrication process.
Sample 1-1 was formed in the following manner: 2,2′-(1,3-phenylene)bis(9-phenyl-1,10-phenanthroline) (abbreviation: mPPhen2P), 4,7-di-1-pyrrolidinyl-1,10-phenanthroline (abbreviation: Pyrrd-Phen), and indium were deposited over a quartz substrate to a thickness of 50 nm such that the volume ratio of mPPhen2P to Pyrrd-Phen and In was 0.5:0.5:0.1. Sample 1-2 was formed in the following manner: mPPhen2P, Pyrrd-Phen, and indium oxide (In2O3) were deposited over a quartz substrate to a thickness of 50 nm such that the volume ratio of mPPhen2P to Pyrrd-Phen and In2O3 was 0.5:0.5:0.1.
As shown above, even when a metal alone is used instead of a metal oxide in formation of the first region in the intermediate layer, the organic EL device of one embodiment of the present invention can be obtained when the metal is changed into an oxide.
Thus, when a region (the first region) including a metal oxide and an organic compound (the first organic compound) having a phenanthroline ring with an electron-donating group is provided instead of an N-type CGL conventionally included in an intermediate layer of a tandem organic EL device, a tandem organic EL device with favorable characteristics can be easily obtained even through an air exposure step.
The intermediate layer of the light-emitting device of one embodiment of the present invention includes at least the first region and a second region that is a P-type CGL as described above. Note that a third region may be provided between the first region and the second region. The formation of the third region allows electrons to be smoothly transferred between the first region and the second region to reduce the driving voltage, and interaction between the first region and the second region to be reduced to improve the reliability, for example.
The first region is provided on the anode side of the intermediate layer and includes a metal oxide and an organic compound (the first organic compound) having a phenanthroline ring with an electron-donating group as described above. The first region is in contact with a light-emitting unit on the anode side. The first region may include a second organic compound in addition to the metal oxide and the organic compound (the first organic compound) having a phenanthroline ring with an electron-donating group.
As the metal oxide included in the first region, an oxide containing an alkali metal (Group 1 element) such as Li, an alkaline earth metal (Group 2 element) such as Mg or Ca, a Group 3 element including Y and lanthanoids such as Eu and Yb, a Group 11 element such as Cu, Ag, or Au, a Group 12 element such as Zn, an earth metal (Group 13 element) such as Al or In, or a Group 14 element such as Sn can be used.
An oxide of an alkali metal or an alkaline earth metal is preferably used as the metal oxide, in which case the donor level formed by interaction between the metal oxide and the first organic compound can be a high energy level; accordingly, electrons generated in the intermediate layer can be smoothly injected and transported to the electron-transport layer, enabling the light-emitting device to have a low driving voltage and emit light with high efficiency. An oxide of the transition metal is preferable because it has low reactivity with components of the air such as water and oxygen. Among the above materials, a metal oxide containing an element belonging to an odd-numbered group (Group 1, 3, 11, or 13) in the periodic table is preferably used, in which case a donor level is easily formed with the first organic compound.
A metal or a metal oxide that has a low melting point and can be deposited by a vacuum evaporation method is preferably used because it can be easily mixed or stacked with an organic compound. Specifically, for example, the metals belonging to Groups 11 and 13 and oxides of the metals have low melting points and thus, they can be suitably used for vacuum evaporation. The metals belonging to Groups 11 and 13 and oxides of the metals are preferable because they are stable with respect to oxygen and water in the air. The metal or the metal oxide that can be deposited by a vacuum evaporation method preferably has a normal-pressure melting point lower than or equal to 2000° C., further preferably lower than or equal to 1500° C., and still further preferably lower than or equal to 1000° C., or a reduced-pressure (vacuum with 1 Pa or less) sublimation temperature lower than or equal to 1500° C., further preferably lower than or equal to 1000° C., and still further preferably lower than or equal to 500° C.
Specifically, lithium oxide, magnesium oxide, calcium oxide, silver oxide, zinc oxide, indium oxide, or the like can be used as the metal oxide, for example. It is also possible to use a material of a metal alone that is oxidized to be a metal oxide in the step of deposition, exposure to the air, or the like as described above. Specific examples of such a metal material include lithium, magnesium, calcium, ytterbium, silver, zinc, aluminum, and indium.
As the first organic compound included in the first region, an organic compound having a phenanthroline ring can be used. An organic compound having a phenanthroline ring with an electron-donating group is preferably used as the first organic compound, in which case the electron density of the phenanthroline ring can be increased.
Among organic compounds having a phenanthroline ring, an organic compound having a 1,10-phenanthroline ring, the two nitrogen atoms of which exist at positions where a metal oxide is easily coordinated, is particularly preferably used to facilitate interaction with the metal oxide.
In the case where an electron-donating group is introduced to a 1,10-phenanthroline ring, the electron-donating group is preferably substituted at the 4-position and the 7-position of the 1,10-phenanthroline ring. Introducing an electron-donating group to the 4- and 7-positions of the 1,10-phenanthroline ring can increase the electron density of the nitrogen atoms at the 1- and 10-positions, thereby facilitating the interaction with the metal oxide.
Specific examples of the electron-donating group include an alkyl group, an alkoxy group, an aryloxy group, an alkylamino group, an arylamino group, and a heterocyclic amino group. Note that examples of the electron-donating group that is preferably introduced to the phenanthroline ring are not limited to the above examples. The electron-donating group may be any group that can increase the electron density of the phenanthroline ring by being introduced to the phenanthroline ring. The electron-donating group may be introduced to the phenanthroline ring via an arylene group such as a phenylene group, and the arylene group is preferably a p-phenylene group.
Specific examples of the alkyl group that can be used as the electron-donating group include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, a sec-butyl group, an isobutyl group, a tert-butyl group, a pentyl group, an isopentyl group, a sec-pentyl group, a tert-pentyl group, a neopentyl group, a hexyl group, an isohexyl group, a sec-hexyl group, a tert-hexyl group, a neohexyl group, a 3-methylpentyl group, a 2-methylpentyl group, a 2-ethylbutyl group, a 1,2-dimethylbutyl group, and a 2,3-dimethylbutyl group.
Specific examples of the alkoxyl group that can be used as the electron-donating group include a methoxy group, an ethoxy group, an n-propoxy group, an isopropoxy group, an n-butoxy group, a sec-butoxy group, an isobutoxy group, a tert-butoxy group, an n-pentyloxy group, an isopentyloxy group, a sec-pentyloxy group, a tert-pentyloxy group, a neopentyloxy group, an n-hexyloxy group, an isohexyloxy group, a sec-hexyloxy group, a tert-hexyloxy group, and a neohexyloxy group.
Specific examples of the aryloxy group that can be used as the electron-donating group include a phenoxy group, an o-tolyloxy group, a m-tolyloxy group, a p-tolyloxy group, a mesityloxy group, an o-biphenyloxy group, a m-biphenyloxy group, a p-biphenyoxyl group, a 1-naphthyloxy group, a 2-naphthyloxy group, and a 2-fluorenyloxy group. Note that the aryloxy group may further have a substituent, and specific examples of the substituent include an alkyl group, an alkoxy group, and a phenyl group.
Specific examples of the alkylamino group that can be used as the electron-donating group include a dimethylamino group and a diethylamino group.
Specific examples of the arylamino group that can be used as the electron-donating group include a diphenylamino group, a bis(α-naphthyl)amino group, and a bis(m-tolyl)amino group. Note that the arylamino group may further have a substituent, and specific examples of the substituent include an alkyl group, an alkoxy group, and a phenyl group.
Specific examples of the heterocyclic amino group that can be used as the electron-donating group include groups represented by Structural Formulae (R-1) to (R-26) below. Note that the heterocyclic amino group may further have a substituent, and specific examples of the substituent include an alkyl group, an alkoxy group, and a phenyl group.
Note that the group represented by Structural Formula (R-1), (R-2), (R-3), (R-4), (R-5), (R-8), (R-9), (R-10), (R-12), (R-14), (R-15), (R-16), (R-17), or (R-21) is further preferably used as the electron-donating group. Among these groups, the group represented by Structural Formula (R-3), (R-4), (R-8), or (R-21) is preferably used because the group has a high electron-donor property and can further increase the electron density of the phenanthroline ring.
Specific examples of the electron-donating group include groups represented by Structural Formulae (R-27) and (R-28) below.
Note that an organic compound with a phenanthroline ring that can be used as the first organic compound may have both the above-described electron-donating group and another substituent. Specific examples of the substituent that can be introduced to the phenanthroline ring together with the above electron-donating group include an aryl group. Specific examples of the aryl group include a phenyl group, an o-tolyl group, a m-tolyl group, a p-tolyl group, a mesityl group, an o-biphenyl group, a m-biphenyl group, a p-biphenyl group, a 1-naphthyl group, a 2-naphthyl group, and a 2-fluorenyl group. Note that the aryl group may further have a substituent, and specific examples of the substituent include an alkyl group, an alkoxy group, and a phenyl group.
Specific examples of an organic compound with a phenanthroline ring that can be used as the first organic compound are represented by Structural Formulae (100) to (107). Note that the organic compound that can be used as the first organic compound is not limited to those examples.
The negative minimum value of the electrostatic potential (ESP) of the first organic compound is preferably small (i.e., the minimum value is preferably a negative value the absolute value of which is large), in which case the efficiency of the interaction with the metal oxide is high.
In an organic compound having a phenanthroline ring, the electrostatic potential around the nitrogen atoms of the phenanthroline ring, which is likely to be negative, can be further lowered (i.e., the absolute value of the negative value can be increased) by introduction of an electron-donating group to the phenanthroline ring.
Note that an electrostatic potential is the energy of interaction between positive point charge with unit quantity of electricity and electron distribution of a molecule. An electrostatic potential value also depends on the threshold value of electron density distribution.
To increase the efficiency of the interaction with the metal oxide, the minimum value of the electrostatic potential of the first organic compound is preferably smaller (negatively larger) than the minimum value of the electrostatic potential of a phenanthroline ring having no substituent.
Specifically, when the threshold value of electron density distribution in atomic units is 0.0004 e/a03 (e represents elementary charge (1 e=1.60218×10−19 C) and a0 represents a Bohr radius (1 a0=5.29177×10−11 m)), the minimum value of the electrostatic potential of the first organic compound is preferably smaller than or equal to −0.085 Eh (Eh represents the Hartree energy (1 Eh=27.211 eV)), further preferably smaller than or equal to −0.090 Eh. When the threshold value of electron density distribution in atomic units is 0.003 e/a03, the minimum value of the electrostatic potential of the first organic compound is preferably smaller than or equal to −0.12 Eh, further preferably smaller than or equal to −0.13 Eh. When the threshold value of electron density distribution in atomic units is 0.0004 e/a03, the minimum value of the ESP of the first organic compound is preferably smaller than or equal to −0.085 Eh, further preferably smaller than or equal to −0.12 Eh when the threshold value of electron density distribution in atomic units is 0.003 e/a03.
The minimum values of the electrostatic potentials (ESP) of the above organic compounds represented by Structural Formulae (100) to (107) above, which can be used as the first organic compound, BPhen, mPPhen2P, NBPhen, Phen, and Hid2Phen were estimated by quantum chemical calculation. Structural Formulae (100) to (107) and the structural formulae of BPhen, mPPhen2P, NBPhen, Phen, and Hid2Phen are shown below.
As the quantum chemistry computational program, Gaussian 09 was used. The calculation was performed using SGI 8600 manufactured by Hewlett Packard Enterprise. The most stable structure of the first organic compound in a ground state was calculated by the density functional theory (DFT). As a basis function, 6-311G(d,p) was used, and as a functional, B3LYP was used.
Table 2 shows the analysis results of the electrostatic potential of the first organic compound in a ground state. Note that an electrostatic potential is the energy of interaction between positive point charge with unit quantity of electricity and electron distribution of a molecule. An electrostatic potential value also depends on the threshold value of electron density. Table 2 shows the electrostatic potentials in electron density distribution at the time when the threshold value of electron density in atomic units is 0.0004 e/a03 or 0.003 e/a03.
From the above table, it is found that the minimum values of ESP of the organic compounds represented by Structural Formulae (100) to (103) and Hid2Phen are each smaller than or equal to −0.085 Eh when the threshold value of electron density distribution in atomic units is 0.0004 e/a03 and that these organic compounds are further preferably used as the first organic compound. It is also found that the minimum values of ESP of the organic compounds represented by Structural Formulae (100) to (103) and Hid2Phen are each smaller than or equal to −0.12 Eh when the threshold value of electron density distribution in atomic units is 0.003 e/a03 and that these organic compounds are further preferably used as the first organic compound.
This is because the organic compounds represented by Structural Formulae (100) to (103) and Hid2Phen have an electron-donating group at each of the 4- and 7-positions of the 1,10-phenantholine ring and thus has a high property of donating electrons to the nitrogen atoms at the 1- and 10-positions of the phenanthroline ring.
It is found that the minimum values of ESP of the organic compounds represented by Structural Formulae (101) and (103) and Hid2Phen are each smaller than or equal to −0.090 Eh when the threshold value of electron density distribution in atomic units is 0.0004 e/a03 and that these organic compounds are particularly preferably used as the first organic compound. It is also found that the minimum values of ESP of the organic compound represented by Structural Formula (103) and Hid2Phen are each smaller than or equal to −0.13 Eh when the threshold value of electron density distribution in atomic units is 0.003 e/a03 and that these organic compounds are particularly preferably used as the first organic compound.
It is found that the organic compound represented by Structural Formula (103) and Hid2Phen are further preferably used as the first organic compound because their minimum values of the ESP are each smaller than or equal to −0.090 Eh when the threshold value of electron density distribution in atomic units is 0.0004 e/a03, and smaller than or equal to −0.13 Eh when the threshold value of electron density distribution in atomic units is 0.003 e/a03.
The first organic compound is preferably strongly basic, in which case the first organic compound interacts with holes to significantly reduce the hole-transport property in the first region of the intermediate layer, enabling the light-emitting device to have high efficiency and a low driving voltage. Specifically, the acid dissociation constant pKa of the first organic compound is preferably higher than or equal to 8, further preferably higher than or equal to 10, still further preferably higher than or equal to 12.
In the case where the acid dissociation constant pKa of an organic compound is unknown, the acid dissociation constants pKa of skeletons in the organic compound are calculated and the largest acid dissociation constant pKa can be regarded as the acid dissociation constant pKa of the organic compound.
The acid dissociation constant may be obtained by calculation. For example, the acid dissociation constant pKa can be obtained by the following calculation method.
The initial structure of a molecule serving as a calculation model is the most stable structure (the singlet ground state) obtained from first-principles calculation.
For the first-principles calculation, Jaguar, which is the quantum chemical computational software manufactured by Schrödinger, Inc., is used, and the most stable structure in the singlet ground state is calculated by the density functional theory (DFT). As a basis function, 6-31G** is used, and as a functional, B3LYP-D3 is used. The structure subjected to quantum chemical calculation is sampled by conformational analysis in mixed torsional/low-mode sampling with Maestro GUI produced by Schrödinger, Inc.
In the calculation of pKa, one or more atoms in each molecule are designated as basic sites, MacroModel is used to search for the stable structure of the protonated molecule in water, conformational search is performed with OPLS2005 force field, and a conformational isomer having the lowest energy is used. Jaguar's pKa calculation module is used. After structure optimization is performed by B3LYP/6-31G*, single point calculation is performed by cc-pVTZ (+) and the pKa value is calculated using empirical correction for functional group(s). In the case where one or more atoms are designated as basic sites in a molecule, the largest of obtained values is used as a pKa value. The obtained pKa values are shown below.
The acid dissociation constant pKa of 2,9hpp2Phen is 13.35, that of 4,7hpp2Phen is 13.42, that of Pyrrd-Phen is 11.23, that of mPPhen2P is 5.16, that of NBPhen is 5.59, and that of BPhen is 5.62.
Next, stabilization energy at the time of interaction between a metal oxide and the first organic compound having a phenanthroline ring with an electron-donating group, and the HOMO level formed at the time of the interaction were estimated by quantum chemical calculation.
As the quantum chemistry computational program, Gaussian 09 was used. The calculation was performed using SGI 8600 manufactured by Hewlett Packard Enterprise. First, the most stable structures of the first organic compound in a ground state, the second organic compound in a ground state, the metal oxide in a ground state, the composite material of the first organic compound and the metal oxide in a ground state, the composite material of the second organic compound and the metal oxide in a ground state, and the composite material of the first organic compound, the second organic compound, and the metal oxide in a ground state were calculated by the density functional theory (DFT). As basis functions, 6-311G(d,p) and LanL2DZ were used, and as a functional, B3LYP was used. Next, the stabilization energy was calculated by subtracting the sum of the total energy of the organic compound(s) alone and the total energy of the metal oxide alone from the total energy of the composite material of the organic compound(s) and the metal oxide. That is, (stabilization energy)=(the total energy of the composite material of the organic compound(s) and the metal oxide)−(the total energy of the organic compound(s) alone)−(the total energy of the metal oxide alone).
The results of the calculation conducted using 4,7-di-1-pyrrolidinyl-1,10-phenanthroline (abbreviation: Pyrrd-Phen) as the first organic compound, 2,2′-(1,3-phenylene)bis(9-phenyl-1,10-phenanthroline) (abbreviation: mPPhen2P) or 2,9-di(naphthalen-2-yl)-4,7-diphenyl-1,10-phenanthroline (abbreviation: NBPhen) as the second organic compound, and silver oxide (Ag2O) or indium oxide (In2O3) as the metal oxide are shown in the table below. Note that the values of the energy levels of HOMO in the table are calculated values and might be different from measured values.
The above table shows that the stabilization energy of the composite material of the silver oxide (Ag2O) and the first organic compound (Pyrrd-Phen) has a negative value, and that the energetic stability in the case of mixing the organic compound and the metal oxide is higher in the case where the organic compound and the metal oxide interact with each other than in the case where the organic compound and the metal do not interact with each other. This is preferable because the composite material forms the HOMO level higher than the HOMO level of the first organic compound (Pyrrd-Phen) and has an excellent electron-injection property.
The composite material of the silver oxide (Ag2O), the first organic compound (Pyrrd-Phen), and the second organic compound (mPPhen2P) is preferable because of having the stabilization energy more stable than that of the composite material of the silver oxide (Ag2O) and the first organic compound (Pyrrd-Phen). The HOMO level formed at this time is higher than the HOMO level of each of the first organic compound (Pyrrd-Phen) and the second organic compound (mPPhen2P) and is further higher than the HOMO level of the composite material of the silver oxide (Ag2O) and the first organic compound (Pyrrd-Phen). The HOMO level is preferably high to achieve a high electron-injection property.
As shown in the above table, indium oxide (In2O3) is preferably used as the metal oxide because the stabilization energy of the composite material of the metal oxide, the first organic compound, and the second organic compound is more stable. The HOMO level formed at this time is higher than the HOMO level of each of the first organic compound and the second organic compound. The HOMO level is preferably high to achieve a high electron-injection property.
In a general fabrication process of a light-emitting device, an EL layer, particularly an intermediate layer, of the light-emitting device is formed by a vacuum evaporation method in many cases. In those cases, it is preferable to use a material that can be easily deposited by vacuum evaporation, i.e., a material with a low melting point. The metal oxides belonging to Groups 11 and 13 have low melting points and thus, they can be suitably used for vacuum evaporation. The metal oxides belonging to Groups 11 and 13 are preferable because they are stable with respect to oxygen and water in the air. A vacuum evaporation method is preferably used, in which case a metal oxide and an organic compound can be easily mixed.
The first region of the intermediate layer preferably includes a second organic compound in addition to the metal oxide and the first organic compound. The second organic compound can improve heat resistance, electron-transport properties, and the like.
As the second organic compound, an organic compound with an electron-transport property can be used. The organic compound with an electron-transport property is preferably a substance having an electron mobility higher than or equal to 1×10−7 cm2/Vs, further preferably higher than or equal to 1×10−6 cm2/Vs, when the square root of electric field strength [V/cm] is 600. Note that any other substance can be used as long as the substance has an electron-transport property higher than a hole-transport property.
An organic compound having a π-electron deficient heteroaromatic ring is preferable as the organic compound with an electron-transport property. The organic compound having a π-electron deficient heteroaromatic ring is preferably one or more of an organic compound having a heteroaromatic ring with an azole skeleton, an organic compound having a heteroaromatic ring with a pyridine skeleton, an organic compound having a heteroaromatic ring with a diazine skeleton, and an organic compound having a heteroaromatic ring with a triazine skeleton.
Specific examples of the organic compound having an electron-transport property include organic compounds having an azole skeleton, such as 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation: PBD), 3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole (abbreviation: TAZ), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene (abbreviation: OXD-7), 9-[4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl]-9H-carbazole (abbreviation: CO11), 2,2′,2″-(1,3,5-benzenetriyl)tris(1-phenyl-1H-benzimidazole) (abbreviation: TPBI), 2-[3-(dibenzothiophen-4-yl)phenyl]-1-phenyl-1H-benzimidazole (abbreviation: mDBTBIm-II), and 4,4′-bis(5-methylbenzoxazol-2-yl)stilbene (abbreviation: BzOs); organic compounds having a heteroaromatic ring having a pyridine skeleton, such as 3,5-bis[3-(9H-carbazol-9-yl)phenyl]pyridine (abbreviation: 35DCzPPy), 1,3,5-tri[3-(3-pyridyl)phenyl]benzene (abbreviation: TmPyPB), bathophenanthroline (abbreviation: BPhen), bathocuproine (abbreviation: BCP), 2,9-di(naphthalen-2-yl)-4,7-diphenyl-1,10-phenanthroline (abbreviation: NBPhen), and 2,2′-(1,3-phenylene)bis(9-phenyl-1,10-phenanthroline) (abbreviation: mPPhen2P); organic compounds having a diazine skeleton, such as 2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTPDBq-II), 2-[3-(3′-dibenzothiophen-4-yl)biphenyl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTBPDBq-II), 2-[3′-(9H-carbazol-9-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline (abbreviation: 2mCzBPDBq), 2-[4′-(9-phenyl-9H-carbazol-3-yl)-3,1′-biphenyl-1-yl]dibenzo[f,h]quinoxaline (abbreviation: 2mpPCBPDBq), 2-[4-(3,6-diphenyl-9H-carbazol-9-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2CzPDBq-III), 7-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 7mDBTPDBq-II), 6-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 6mDBTPDBq-II), 9-[3′-(dibenzothiophen-4-yl)biphenyl-3-yl]naphtho[1′,2′:4,5]furo[2,3-b]pyrazine (abbreviation: 9mDBtBPNfpr), 9-[3′-(dibenzothiophen-4-yl)biphenyl-4-yl]naphtho[1′,2′:4,5]furo[2,3-b]pyrazine (abbreviation: 9pmDBtBPNfpr), 4,6-bis[3-(phenanthren-9-yl)phenyl]pyrimidine (abbreviation: 4,6mPnP2Pm), 4,6-bis[3-(dibenzothiophen-4-yl)phenyl]pyrimidine (abbreviation: 4,6mDBTP2Pm-II), 4,6-bis[3-(9H-carbazol-9-yl)phenyl]pyrimidine (abbreviation: 4,6mCzP2Pm), 9,9′-[pyrimidine-4,6-diylbis(biphenyl-3,3′-diyl)]bis(9H-carbazole) (abbreviation: 4,6mCzBP2Pm), 8-(biphenyl-4-yl)-4-[3-(dibenzothiophen-4-yl)phenyl]-[1]benzofuro[3,2-d]pyrimidine (abbreviation: 8BP-4mDBtPBfpm), 3,8-bis[3-(dibenzothiophen-4-yl)phenyl]benzofuro[2,3-b]pyrazine (abbreviation: 3,8mDBtP2Bfpr), 4,8-bis[3-(dibenzothiophen-4-yl)phenyl]-[1]benzofuro[3,2-d]pyrimidine (abbreviation: 4,8mDBtP2Bfpm), 8-[3′-(dibenzothiophen-4-yl)biphenyl-3-yl)]naphtho[1′,2′:4,5]furo[3,2-d]pyrimidine (abbreviation: 8mDBtBPNfpm), 8-[(2,2′-binaphthalen)-6-yl]-4-[3-(dibenzothiophen-4-yl)phenyl]-[1]benzofuro[3,2-d]pyrimidine (abbreviation: 8(βN2)-4mDBtPBfpm), 2,2′-(pyridine-2,6-diyl)bis(4-phenylbenzo[h]quinazoline) (abbreviation: 2,6(P-Bqn)2Py), 2,2′-(pyridine-2,6-diyl)bis{4-[4-(2-naphthyl)phenyl]-6-phenylpyrimidine} (abbreviation: 2,6(NP-PPm)2Py), 6-(biphenyl-3-yl)-4-[3,5-bis(9H-carbazol-9-yl)phenyl]-2-phenylpyrimidine (abbreviation: 6mBP-4Cz2PPm), 2,6-bis(4-naphthalen-1-ylphenyl)-4-[4-(3-pyridyl)phenyl]pyrimidine (abbreviation: 2,4NP-6PyPPm), 4-[3,5-bis(9H-carbazol-9-yl)phenyl]-2-phenyl-6-(biphenyl-4-yl)pyrimidine (abbreviation: 6BP-4Cz2PPm), and 7-[4-(9-phenyl-9H-carbazol-2-yl)quinazolin-2-yl]-7H-dibenzo[c,g]carbazole (abbreviation: PC-cgDBCzQz); and organic compounds having a triazine skeleton, such as 2-(biphenyl-4-yl)-4-phenyl-6-(9,9′-spirobi[9H-fluoren]-2-yl)-1,3,5-triazine (abbreviation: BP-SFTzn), 2-{3-[3-(benzo[b]naphtho[1,2-d]furan-8-yl)phenyl]phenyl}-4,6-diphenyl-1,3,5-triazine (abbreviation: mBnfBPTzn), 2-{3-[3-(benzo[b]naphtho[1,2-d]furan-6-yl)phenyl]phenyl}-4,6-diphenyl-1,3,5-triazine (abbreviation: mBnfBPTzn-02), 2-{4-[3-(N-phenyl-9H-carbazol-3-yl)-9H-carbazol-9-yl]phenyl}-4,6-diphenyl-1,3,5-triazine (abbreviation: PCCzPTzn), 9-[3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl]-9′-phenyl-2,3′-bi-9H-carbazole (abbreviation: mPCCzPTzn-02), 2-[3′-(9,9-dimethyl-9H-fluoren-2-yl)biphenyl-3-yl]-4,6-diphenyl-1,3,5-triazine (abbreviation: mFBPTzn), 5-[3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl]-7,7-dimethyl-5H,7H-indeno[2,1-b]carbazole (abbreviation: mINc(II)PTzn), 2-{3-[3-(dibenzothiophen-4-yl)phenyl]phenyl}-4,6-diphenyl-1,3,5-triazine (abbreviation: mDBtBPTzn), 2,4,6-tris[3′-(pyridin-3-yl)biphenyl-3-yl]-1,3,5-triazine (abbreviation: TmPPPyTz), 2-[3-(2,6-dimethyl-3-pyridinyl)-5-(9-phenanthrenyl)phenyl]-4,6-diphenyl-1,3,5-triazine (abbreviation: mPn-mDMePyPTzn), 11-[4-(biphenyl-4-yl)-6-phenyl-1,3,5-triazin-2-yl]-11,12-dihydro-12-phenylindolo[2,3-a]carbazole (abbreviation: BP-Icz(II)Tzn), 2-[3′-(triphenylen-2-yl)biphenyl-3-yl]-4,6-diphenyl-1,3,5-triazine (abbreviation: mTpBPTzn), 3-[9-(4,6-diphenyl-1,3,5-triazin-2-yl)-2-dibenzofuranyl]-9-phenyl-9H-carbazole (abbreviation: PCDBfTzn), and 2-(biphenyl-3-yl)-4-phenyl-6-{8-[(1,1′:4′,1″-terphenyl)-4-yl]-1-dibenzofuranyl}-1,3,5-triazine (abbreviation: mBP-TPDBfTzn).
Among the above, organic compounds having a phenanthroline ring, such as BPhen, BCP, NBPhen, and mPPhen2P, are preferred, and an organic compound having a phenanthroline ring dimeric structure, such as mPPhen2P, is further preferred because of its excellent heat resistance and stability.
The second organic compound preferably has 25 to 100 carbon atoms. When having 25 to 100 carbon atoms, the second organic compound can have excellent sublimability, and thus, thermal decomposition of the organic compound during vacuum evaporation can be inhibited and the efficiency of use of the material can be high.
An organic compound having a glass transition temperature Tg higher than or equal to 100° C. is preferably used as the second organic compound. In that case, the intermediate layer is not easily crystallized. Accordingly, the intermediate layer has high heat resistance and is not easily crystallized. Thus, the intermediate layer is not easily crystallized even when part of the organic compound layer is processed by a lithography technique.
Examples of an organic compound having a phenanthroline ring and a glass transition temperature (Tg) higher than or equal to 100° C. include NBPhen (Tg: 165° C.), mPPhen2P (Tg: 135° C.), 2,2′-(biphenyl-4,4′-diyl)bis(9-phenyl-1,10-phenanthroline) (abbreviation: PPhen2BP) (Tg: 166° C.), 2,2′-biphenyl-3,3′-diylbis(9-phenyl-1,10-phenanthroline) (abbreviation: mPPhen2BP) (Tg: 144° C.), 2,8-bis(phenanthrolin-5-yl)dibenzofuran (abbreviation: 2,8Phen2DBf) (Tg: 210° C.), and 5,5′,5″-(benzene-1,3,5-triyl)tri-1,10-phenanthroline (abbreviation: Phen3P) (Tg: 257° C.).
As the second organic compound, an organic compound with an acid dissociation constant pKa higher than or equal to 4 and lower than 8 can be used. The second organic compound preferably has such an acid dissociation constant to have a poor hole-transport property, in which case the hole-transport property in the first region of the intermediate layer can be reduced and hole transport from the first region to the P-type CGL can be prevented, enabling the light-emitting device to have high efficiency. An excessively high acid dissociation constant pKa leads to high solubility in water and thus reduces the resistance to water and a chemical solution used in the process with a lithography technique. Thus, the acid dissociation constant pKa of the second organic compound is preferably higher than or equal to 4 and lower than 8.
Note that the LUMO level of the second organic compound is further preferably lower than that of the first organic compound. In that case, electrons can be easily donated from the donor level formed by the first organic compound and the metal oxide to the second organic compound. The LUMO level of the second organic compound is preferably lower than that of the first organic compound also because the second organic compound preferably has an electron-transport property.
The LUMO level of the second organic compound is preferably higher than or equal to −3.0 eV and lower than or equal to −2.0 eV, further preferably higher than or equal to −3.0 eV and lower than or equal to −2.5 eV. The LUMO level of the first organic compound is preferably higher than or equal to −3.0 eV and lower than or equal to −2.0 eV, further preferably higher than or equal to −2.7 eV and lower than or equal to −2.0 eV.
In the above case, electrons can be easily donated from the donor level formed by the first organic compound and the metal oxide to the second organic compound. In addition, electrons in the second organic compound can be easily transported.
Note that the HOMO level and the LUMO level of an organic compound are generally estimated by cyclic voltammetry (CV), photoelectron spectroscopy, optical absorption spectroscopy, inverse photoemission spectroscopy, or the like. When values of different compounds are compared with each other, it is preferable that values estimated by the same measurement be used.
The first region preferably includes the second organic compound in addition to the metal oxide and the first organic compound, in which case interaction between materials occurs efficiently. This can be confirmed by measurement of spin density by electron spin resonance (ESR).
For example, the spin density measured by ESR of a film that includes the metal oxide and the first organic compound is preferably higher than that of a film that includes the metal and the second organic compound. The spin density measured by ESR of a film that includes the metal oxide, the first organic compound, and the second organic compound is preferably higher than that of a film that includes any two of the metal oxide, the first organic compound, and the second organic compound. In that case, interaction between the materials is found to occur efficiently.
More specifically, in the film that includes the metal oxide and the first organic compound, the density of spins attributed to a signal observed at a g-factor of approximately 2.00 is measured by an electron spin resonance method to be, for example, higher than or equal to 5×1016 spins/cm3, preferably higher than or equal to 1×1017 spins/cm3. In such a case, it can be confirmed that the interaction between the materials occurs efficiently in the film that includes the metal oxide and the first organic compound. Alternatively, in the film that includes the metal oxide, the first organic compound, and the second organic compound, the density of spins attributed to a signal observed at a g-factor of approximately 2.00 is measured by an electron spin resonance method to be, for example, higher than or equal to 5×1016 spins/cm3, preferably higher than or equal to 1×1017 spins/cm3. In such a case, it can be confirmed that the interaction between the materials occurs more efficiently in the film that includes the metal oxide, the first organic compound, and the second organic compound than in the film that includes only two of the metal oxide, the first organic compound, and the second organic compound. The density of spins attributed to a signal observed at a g-factor of approximately 2.00 is measured by an electron spin resonance method to be, for example, lower than or equal to 2×1016 spins/cm3 in a mixed film that includes the metal oxide and the second organic compound. The density of spins attributed to a signal observed at a g-factor of approximately 2.00 is measured by an electron spin resonance method to be, for example, lower than or equal to 2×1016 spins/cm3 in a mixed film that includes the first organic compound and the second organic compound.
In the first region, the molar ratio of the metal oxide to the first organic compound (or the sum of the first organic compound and the second organic compound) is preferably greater than or equal to 0.1 and less than or equal to 10, further preferably greater than or equal to 0.2 and less than or equal to 5, still further preferably greater than or equal to 0.5 and less than or equal to 2. Alternatively, the volume ratio of the metal oxide to the first organic compound (the sum of the first organic compound and the second organic compound) is preferably greater than or equal to 0.01 and less than or equal to 0.3, further preferably greater than or equal to 0.02 and less than or equal to 0.2, still further preferably greater than or equal to 0.05 and less than or equal to 0.1. Mixing the metal oxide and the first organic compound (or the first organic compound and the second organic compound) in such a ratio enables providing the intermediate layer having a favorable electron-injection property. Although the second organic compound is not necessarily used, the volume ratio of the first organic compound to the second organic compound is preferably greater than or equal to 0.1 and less than or equal to 10, further preferably greater than or equal to 0.2 and less than or equal to 5, still further preferably greater than or equal to 0.5 and less than or equal to 2. Mixing the first organic compound and the second organic compound in such a ratio enables providing the intermediate layer having a favorable electron-transport property. When an organic compound with favorable thermophysical properties with high Tg is used as the second organic compound, highly reliable organic EL device can be provided.
The thickness of the first region is preferably greater than or equal to 2 nm and less than or equal to 20 nm, further preferably greater than or equal to 5 nm and less than or equal to 10 nm. In the case where the first region has a stacked-layer structure of a metal oxide layer and a layer containing the first organic compound, the layer of the metal oxide is preferably greater than or equal to 0.1 nm and less than or equal to 5 nm, further preferably greater than or equal to 0.2 nm and less than or equal to 2 nm. In the case where the first region has a stacked-layer structure of a metal oxide layer and a layer containing the first organic compound, the layer containing the first organic compound is preferably greater than or equal to 2 nm and less than or equal to 20 nm, further preferably greater than or equal to 5 nm and less than or equal to 10 nm.
The second region is a P-type CGL and preferably formed using a composite material containing an organic compound having a hole-transport property (a third organic compound) and a material having an electron-acceptor property with respect to the organic compound having a hole-transport property.
As the material having an electron-acceptor property with respect to the organic compound having a hole-transport property, an organic compound having an electron-withdrawing group (e.g., a halogen group or a cyano group) can be used, and it is further preferable to use an organic compound having four or more halogen groups, four or more cyano groups, or a combination of a halogen group and a cyano group the number of which is four or more. Specific examples include 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation: F4-TCNQ), chloranil, 2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylene (abbreviation: HAT-CN), 1,3,4,5,7,8-hexafluorotetracyano-naphthoquinodimethane (abbreviation: F6-TCNNQ), and 2-(7-dicyanomethylen-1,3,4,5,6,8,9,10-octafluoro-7H-pyren-2-ylidene)malononitrile. A compound in which electron-withdrawing groups are bonded to a condensed aromatic ring having a plurality of heteroatoms, such as HAT-CN, is particularly preferable because it is thermally stable. A [3]radialene derivative having an electron-withdrawing group (in particular, a cyano group, a halogen group such as a fluoro group, or the like) has a very high electron-acceptor property and thus is preferable. Specific examples include α,α′,α″-1,2,3-cyclopropanetriylidenetris[4-cyano-2,3,5,6-tetrafluorobenzeneacetonitrile], α,α′,α″-1,2,3-cyclopropanetriylidenetris[2,6-dichloro-3,5-difluoro-4-(trifluoromethyl)benzeneacetonitrile], and α,α′,α″-1,2,3-cyclopropanetriylidenetris[2,3,4,5,6-pentafluorobenzeneacetonitrile].
As the material having an electron-acceptor property, a transition metal oxide such as molybdenum oxide, vanadium oxide, ruthenium oxide, tungsten oxide, or manganese oxide can be used, other than the above-described organic compounds. In that case, one embodiment of the present invention can be regarded as a light-emitting device in which a P-type CGL and an N-type CGL in an intermediate layer contain different metal oxides. Alternatively, the light-emitting device can be regarded as a light-emitting device in which a P-type CGL and an N-type CGL contain different metal oxides and organic compounds. When the metal oxide, which is stable, is used for both of the P-type CGL and the N-type CGL, a tandem light-emitting device including an intermediate layer that is stable against oxygen and water in the air and water and a chemical solution used during the manufacturing process can be fabricated.
As the hole-transport organic compound used in the composite material, any of a variety of organic compounds such as aromatic amine compounds, heteroaromatic compounds, aromatic hydrocarbons, and high molecular compounds (e.g., oligomers, dendrimers, and polymers) can be used. Note that the hole-transport organic compound used in the composite material preferably has a hole mobility higher than or equal to 1×10−6 cm2/Vs. The hole-transport organic compound used in the composite material is preferably a compound having a condensed aromatic hydrocarbon ring or a π-electron rich heteroaromatic ring. As the condensed aromatic hydrocarbon ring, an anthracene ring, a naphthalene ring, or the like is preferable. As the π-electron rich heteroaromatic ring, a condensed aromatic ring having at least one of a pyrrole skeleton, a furan skeleton, and a thiophene skeleton is preferable; specifically, a carbazole ring, a dibenzothiophene ring, or a ring in which an aromatic ring or a heteroaromatic ring is further fused to the carbazole ring or the dibenzothiophene ring is preferable.
Such an organic compound with a hole-transport property further preferably has any of a carbazole skeleton, a dibenzofuran skeleton, a dibenzothiophene skeleton, and an anthracene skeleton. In particular, an aromatic amine having a substituent with a dibenzofuran ring or a dibenzothiophene ring, an aromatic monoamine having a naphthalene ring, or an aromatic monoamine in which a 9-fluorenyl group is bonded to the nitrogen of the amine through an arylene group may be used. Note that the organic compound with a hole-transport property preferably has an N,N-bis(4-biphenyl)amino group to enable fabrication of a light-emitting device having a long lifetime.
Specific examples of the organic compound with a hole-transport property include N-(4-biphenyl)-6,N-diphenylbenzo[b]naphtho[1,2-d]furan-8-amine (abbreviation: BnfABP), N,N-bis(4-biphenyl)-6-phenylbenzo[b]naphtho[1,2-d]furan-8-amine (abbreviation: BBABnf), 4,4′-bis(6-phenylbenzo[b]naphtho[1,2-d]furan-8-yl)-4″-phenyltriphenylamine (abbreviation: BnfBB1BP), N,N-bis(4-biphenyl)benzo[b]naphtho[1,2-d]furan-6-amine (abbreviation: BBABnf(6)), N,N-bis(4-biphenyl)benzo[b]naphtho[1,2-d]furan-8-amine (abbreviation: BBABnf(8)), N,N-bis(4-biphenyl)benzo[b]naphtho[2,3-d]furan-4-amine (abbreviation: BBABnf(II)(4)), N,N-bis[4-(dibenzofuran-4-yl)phenyl]-4-amino-p-terphenyl (abbreviation: DBfBB1TP), N-[4-(dibenzothiophen-4-yl)phenyl]-N-phenyl-4-biphenylamine (abbreviation: ThBA1BP), 4-(2-naphthyl)-4′,4″-diphenyltriphenylamine (abbreviation: BBAβNB), 4-[4-(2-naphthyl)phenyl]-4′,4″-diphenyltriphenylamine (abbreviation: BBAβNBi), 4,4′-diphenyl-4″-(6;1′-binaphthyl-2-yl)triphenylamine (abbreviation: BBAαNβNB), 4,4′-diphenyl-4″-(7;1′-binaphthyl-2-yl)triphenylamine (abbreviation: BBAαNβNB-03), 4,4′-diphenyl-4″-(7-phenyl)naphthyl-2-yltriphenylamine (abbreviation: BBAPβNB-03), 4,4′-diphenyl-4″-(6;2′-binaphthyl-2-yl)triphenylamine (abbreviation: BBA(βN2)B), 4,4′-diphenyl-4″-(7;2′-binaphthyl-2-yl)triphenylamine (abbreviation: BBA(βN2)B-03), 4,4′-diphenyl-4″-(4;2′-binaphthyl-1-yl)triphenylamine (abbreviation: BBAβNαNB), 4,4′-diphenyl-4″-(5;2′-binaphthyl-1-yl)triphenylamine (abbreviation: BBAβNαNB-02), 4-(4-biphenylyl)-4′-(2-naphthyl)-4″-phenyltriphenylamine (abbreviation: TPBiAβNB), 4-(3-biphenylyl)-4′-[4-(2-naphthyl)phenyl]-4″-phenyltriphenylamine (abbreviation: mTPBiAβNBi), 4-(4-biphenylyl)-4′-[4-(2-naphthyl)phenyl]-4″-phenyltriphenylamine (abbreviation: TPBiAβNBi), 4-phenyl-4′-(1-naphthyl)triphenylamine (abbreviation: αNBA1BP), 4,4′-bis(1-naphthyl)triphenylamine (abbreviation: αNBB1BP), 4,4′-diphenyl-4″-[4′-(carbazol-9-yl)biphenyl-4-yl]triphenylamine (abbreviation: YGTBi1BP), 4′-[4-(3-phenyl-9H-carbazol-9-yl)phenyl]tris(biphenyl-4-yl)amine (abbreviation: YGTBi1BP-02), 4-[4′-(carbazol-9-yl)biphenyl-4-yl]-4′-(2-naphthyl)-4″-phenyltriphenylamine (abbreviation: YGTBiPNB), N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-N-[4-(1-naphthyl)phenyl]-9,9′-spirobi[9H-fluoren]-2-amine (abbreviation: PCBNBSF), N,N-bis(biphenyl-4-yl)-9,9′-spirobi[9H-fluoren]-2-amine (abbreviation: BBASF), N,N-bis(biphenyl-4-yl)-9,9′-spirobi[9H-fluoren]-4-amine (abbreviation: BBASF(4)), N-(biphenyl-2-yl)-N-(9,9-dimethyl-9H-fluoren-2-yl)-9,9′-spirobi[9H-fluoren]-4-amine (abbreviation: oFBiSF), N-(biphenyl-4-yl)-N-(9,9-dimethyl-9H-fluoren-2-yl)dibenzofuran-4-amine (abbreviation: FrBiF), N-[4-(1-naphthyl)phenyl]-N-[3-(6-phenyldibenzofuran-4-yl)phenyl]-1-naphthylamine (abbreviation: mPDBfBNBN), 4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP), 4-phenyl-3′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: mBPAFLP), 4-phenyl-4′-[4-(9-phenylfluoren-9-yl)phenyl]triphenylamine (abbreviation: BPAFLBi), 4-phenyl-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBA1BP), 4,4′-diphenyl-4″-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBBi1BP), 4-(1-naphthyl)-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBANB), 4,4′-di(1-naphthyl)-4″-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBNBB), N-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9′-spirobi[9H-fluoren]-2-amine (abbreviation: PCBASF), N-(biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H-fluoren-2-amine (abbreviation: PCBBiF), N,N-bis(9,9-dimethyl-9H-fluoren-2-yl)-9,9′-spirobi-9H-fluoren-4-amine, N,N-bis(9,9-dimethyl-9H-fluoren-2-yl)-9,9′-spirobi-9H-fluoren-3-amine, N,N-bis(9,9-dimethyl-9H-fluoren-2-yl)-9,9′-spirobi-9H-fluoren-2-amine, and N,N-bis(9,9-dimethyl-9H-fluoren-2-yl)-9,9′-spirobi-9H-fluoren-1-amine.
As the material with a hole-transport property, any of the following aromatic amine compounds can also be used: N,N′-di(p-tolyl)-N,N′-diphenyl-p-phenylenediamine (abbreviation: DTDPPA), 4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (abbreviation: DPAB), 4,4′-bis(N-{4-[N′-(3-methylphenyl)-N′-phenylamino]phenyl}-N-phenylamino)biphenyl (abbreviation: DNTPD), and 1,3,5-tris[N-(4-diphenylaminophenyl)-N-phenylamino]benzene (abbreviation: DPA3B).
The material having an electron-acceptor property in the P-type CGL preferably has a property of accepting electrons. The material having an electron-acceptor property preferably has an electron-acceptor property with respect to a hole-transport organic compound. When the material having an electron-acceptor property has an electron-acceptor property, the P-type CGL can function as a carrier-generation layer owing to charge separation in the P-type CGL and thus can function as an intermediate layer of a tandem light-emitting device. A signal is preferably observed by electron spin resonance in the P-type CGL. For example, the density of spins attributed to a signal observed at a g-factor of approximately 2.00 is preferably higher than or equal to 1×1017 spins/cm3, further preferably higher than or equal to 1×1018 spins/cm3, still further preferably higher than or equal to 1×1019 spins/cm3.
A third region may be provided between the first region and the second region in the intermediate layer.
The third region contains a substance having an electron-transport property and has functions of smoothly transferring and receiving electrons between the first region and the second region to reduce the driving voltage, and reducing the interaction between the first region and the second region to improve the reliability, for example.
The LUMO level of the electron-transport substance included in the third region is preferably between the LUMO level of the acceptor substance in the second region and the LUMO level of the organic compound included in a layer which is included in the light-emitting unit on the anode side and is in contact with the intermediate layer.
As a specific energy level of the LUMO level of the electron-transport substance used in the third region is preferably higher than or equal to −5.0 eV, further preferably higher than or equal to −5.0 eV and lower than or equal to −3.0 eV, still further preferably higher than or equal to −4.30 eV and lower than or equal to −3.00 eV, yet still further preferably higher than or equal to −4.30 eV and lower than or equal to −3.30 eV, in which case an increase in driving voltage can be inhibited. Note that as the electron-transport substance used in the third region, a phthalocyanine-based material or a metal complex having a metal-oxygen bond and an aromatic ligand is preferably used.
Specific examples of the electron-transport substance used in the third region include a perylenetetracarboxylic acid derivative such as diquinoxalino[2,3-α:2′,3′-c]phenazine (abbreviation: HATNA), 2,3,8,9,14,15-hexafluorodiquinoxalino[2,3-α:2′,3′-c]phenazine (abbreviation: HATNA-F6), 3,4,9,10-perylenetetracarboxylic diimide (abbreviation: PTCDI), or 3,4,9,10-perylenetetracarboxyl-bis-benzimidazole (abbreviation: PTCBI), (C60—Ih)[5,6]fullerene (abbreviation: C60), and (C70-D5h)[5,6]fullerene (abbreviation: C70). It is also possible to use a compound having a heterophane skeleton, which is a cyclophane skeleton including a hetero ring; for example, a phthalocyanine compound such as phthalocyanine (abbreviation: H2Pc) can be used as the compound. Alternatively, it is possible to use a metal phthalocyanine containing copper, zinc, cobalt, iron, chromium, nickel, or the like or a derivative thereof, such as copper phthalocyanine (abbreviation: CuPc), zinc phthalocyanine (abbreviation: ZnPc), cobalt phthalocyanine (abbreviation: CoPc), iron phthalocyanine (abbreviation: FePc), tin phthalocyanine (abbreviation: SnPc), tin oxide phthalocyanine (abbreviation: SnOPc), titanium oxide phthalocyanine (abbreviation: TiOPc), or vanadium oxide phthalocyanine (abbreviation: VOPc). It is particularly preferable to use a phthalocyanine-based metal complex such as copper phthalocyanine or zinc phthalocyanine or 2,3,8,9,14,15-hexafluorodiquinoxalino[2,3-α:2′,3′-c]phenazine.
The thickness of the third region is preferably greater than or equal to 1 nm and less than or equal to 10 nm, further preferably greater than or equal to 2 nm and less than or equal to 5 nm.
The light-emitting device of one embodiment of the present invention having the aforementioned structure can exhibit favorable characteristics even when exposure to the air or a photolithography process involving exposure to the air is performed before the second electrode is formed.
In this embodiment, light-emitting devices of one embodiment of the present invention will be described in detail.
The first light-emitting unit 501 includes at least a first light-emitting layer 113_1, and the second light-emitting unit 502 includes at least a second light-emitting layer 113_2. The first light-emitting layer 113_1 and the second light-emitting layer 113_2 are each a layer containing a light-emitting substance and emit light when voltage is applied between the first electrode 101 and the second electrode 102.
The first light-emitting unit 501 preferably includes, in addition to the above-described layers, functional layers such as a hole-injection layer 111, a first hole-transport layer 112_1, and first electron-transport layer 114_1 as illustrated in
The second light-emitting unit 502 preferably includes, in addition to the above-described layers, functional layers such as a second hole-transport layer 112_2, a second electron-transport layer 114_2, and an electron-injection layer 115 as illustrated in
Furthermore, the intermediate layer 116 includes at least a first region 119, a third region 118, and a second region 117 from the anode (the first electrode 101 in
Since the structures of the first region 119, the second region 117, and the third region 118 have been specifically described in detail in Embodiment 1, repetitive descriptions thereof are omitted.
The first electrode 101 includes an anode and the second electrode 102 includes a cathode in this embodiment. The first electrode 101 and the second electrode 102 may each have a single-layer structure or a stacked-layer structure. In the case of the stacked-layer structure, a layer in contact with the organic compound layer 103 serves as an anode or a cathode. In the case where the electrodes each have the stacked-layer structure, there is no limitation on work functions of materials for layers other than the layer in contact with the organic compound layer 103, and the materials can be selected in accordance with required properties such as a resistance value, processing easiness, reflectivity, light-transmitting property, and stability.
The anode is preferably formed using any of metals, alloys, and conductive compounds with a high work function (specifically, higher than or equal to 4.0 eV), mixtures thereof, and the like. Specific examples include indium oxide-tin oxide (ITO: indium tin oxide), indium oxide-tin oxide containing silicon or silicon oxide (ITSO: indium tin silicon oxide), indium oxide-zinc oxide, and indium oxide containing tungsten oxide and zinc oxide (IWZO). Films of such conductive metal oxides are usually formed by a sputtering method, but may be formed by application of a sol-gel method or the like. For example, a film of indium oxide-zinc oxide is formed by a sputtering method using a target in which 1 wt % to 20 wt % zinc oxide is added to indium oxide. Furthermore, a film of indium oxide containing tungsten oxide and zinc oxide (IWZO) can be formed by a sputtering method using a target in which 0.5 wt % to 5 wt % tungsten oxide and 0.1 wt % to 1 wt % zinc oxide are added to indium oxide. Alternatively, gold (Au), platinum (Pt), nickel (Ni), tungsten (W), chromium (Cr), molybdenum (Mo), iron (Fe), cobalt (Co), copper (Cu), palladium (Pd), titanium, (Ti), aluminum (Al), nitride of a metal material (e.g., titanium nitride), or the like can be used for the anode. The anode may be a stack of layers formed of any of these materials. For example, a film in which Al, Ti, and ITSO are stacked in this order over Ti is preferable because the film has high efficiency owing to high reflectivity and enables high resolution of several thousand ppi. Graphene can also be used for the anode. When a composite material that can be included in the hole-injection layer 111, which is described later, is used for a layer (typically, the hole-injection layer) in contact with the anode, an electrode material can be selected regardless of its work function.
The hole-injection layer 111 is provided in contact with the anode and has a function of facilitating injection of holes to the organic compound layer 103. The hole-injection layer 111 can be formed using a phthalocyanine-based compound or complex compound such as phthalocyanine (abbreviation: H2Pc) or copper phthalocyanine (abbreviation: CuPc), an aromatic amine compound such as 4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (abbreviation: DPAB) or 4,4′-bis(N-{4-[N-(3-methylphenyl)-N′-phenylamino]phenyl}-N-phenylamino) biphenyl (abbreviation: DNTPD), or a high molecular compound such as poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonic acid) (abbreviation: PEDOT/PSS).
The hole-injection layer 111 may be formed using a substance having an electron-acceptor property. Examples of the substance having an electron-acceptor property include organic compounds having an electron-withdrawing group (a halogen group or a cyano group), such as 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation: F4-TCNQ), chloranil, 2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylene (abbreviation: HAT-CN), 1,3,4,5,7,8-hexafluorotetracyano-naphthoquinodimethane (abbreviation: F6-TCNNQ), and 2-(7-dicyanomethylen-1,3,4,5,6,8,9,10-octafluoro-7H-pyren-2-ylidene) malononitrile. A compound in which electron-withdrawing groups are bonded to a condensed aromatic ring having a plurality of heteroatoms, such as HAT-CN, is particularly preferable because it is thermally stable. A [3] radialene derivative having an electron-withdrawing group (in particular, a cyano group, a halogen group such as a fluoro group, or the like) has a significantly high electron-acceptor property and thus is preferable. Specific examples include α,α′,α″-1,2,3-cyclopropanetriylidenetris[4-cyano-2,3,5,6-tetrafluorobenzeneacetonitrile], α,α′,α″-1,2,3-cyclopropanetriylidenetris[2,6-dichloro-3,5-difluoro-4-(trifluoromethyl)benzeneacetonitrile], and α,α′,α″-1,2,3-cyclopropanetriylidenetris[2,3,4,5,6-pentafluorobenzeneacetonitrile]. As the substance having an electron-acceptor property, a transition metal oxide such as molybdenum oxide, vanadium oxide, ruthenium oxide, tungsten oxide, or manganese oxide can be used, other than the above-described organic compounds.
The hole-injection layer 111 is preferably formed using a composite material containing any of the aforementioned materials having an electron-acceptor property and an organic compound having a hole-transport property.
As the organic compound having a hole-transport property used in the composite material, any of a variety of organic compounds such as aromatic amine compounds, heteroaromatic compounds, aromatic hydrocarbons, and high molecular compounds (e.g., oligomers, dendrimers, and polymers) can be used. Note that the organic compound having a hole-transport property used in the composite material preferably has a hole mobility higher than or equal to 1×10−6 cm2/Vs. The organic compound having a hole-transport property used in the composite material preferably has a condensed aromatic hydrocarbon ring or a π-electron rich heteroaromatic ring. As the condensed aromatic hydrocarbon ring, an anthracene ring, a naphthalene ring, or the like is preferable. As the π-electron rich heteroaromatic ring, a condensed aromatic ring having at least one of a pyrrole skeleton, a furan skeleton, and a thiophene skeleton in the ring is preferable; specifically, a carbazole ring, a dibenzothiophene ring, or a ring in which an aromatic ring or a heteroaromatic ring is further condensed to a carbazole ring or a dibenzothiophene ring is preferable.
Such an organic compound having a hole-transport property further preferably has any of a carbazole skeleton, a dibenzofuran skeleton, a dibenzothiophene skeleton, and an anthracene skeleton. In particular, an aromatic amine having a substituent that has a dibenzofuran ring or a dibenzothiophene ring, an aromatic monoamine that has a naphthalene ring, or an aromatic monoamine in which a 9-fluorenyl group is bonded to nitrogen of an amine through an arylene group may be used. Note that the organic compound having a hole-transport property preferably has an N,N-bis(4-biphenyl)amino group to enable fabricating a light-emitting device with a long lifetime.
Specific examples of the organic compound having a hole-transport property include N-(4-biphenyl)-6,N-diphenylbenzo[b]naphtho[1,2-d]furan-8-amine (abbreviation: BnfABP), N,N-bis(4-biphenyl)-6-phenylbenzo[b]naphtho[1,2-d]furan-8-amine (abbreviation: BBABnf), 4,4′-bis(6-phenylbenzo[b]naphtho[1,2-d]furan-8-yl)-4″-phenyltriphenylamine (abbreviation: BnfBB1BP), N,N-bis(4-biphenyl)benzo[b]naphtho[1,2-d]furan-6-amine (abbreviation: BBABnf(6)), N,N-bis(4-biphenyl)benzo[b]naphtho[1,2-d]furan-8-amine (abbreviation: BBABnf(8)), N,N-bis(4-biphenyl)benzo[b]naphtho[2,3-d]furan-4-amine (abbreviation: BBABnf(II)(4)), N,N-bis[4-(dibenzofuran-4-yl)phenyl]-4-amino-p-terphenyl (abbreviation: DBfBB1TP), N-[4-(dibenzothiophen-4-yl)phenyl]-N-phenyl-4-biphenylamine (abbreviation: ThBA1BP), 4-(2-naphthyl)-4′,4″-diphenyltriphenylamine (abbreviation: BBAβNB), 4-[4-(2-naphthyl)phenyl]-4′,4″-diphenyltriphenylamine (abbreviation: BBAβNBi), 4,4′-diphenyl-4″-(6;1′-binaphthyl-2-yl)triphenylamine (abbreviation: BBAαNβNB), 4,4′-diphenyl-4″-(7;1′-binaphthyl-2-yl)triphenylamine (abbreviation: BBAαNβNB-03), 4,4′-diphenyl-4″-(7-phenyl)naphthyl-2-yltriphenylamine (abbreviation: BBAPβNB-03), 4,4′-diphenyl-4″-(6;2′-binaphthyl-2-yl)triphenylamine (abbreviation: BBA(βN2)B), 4,4′-diphenyl-4″-(7;2′-binaphthyl-2-yl)triphenylamine (abbreviation: BBA(βN2)B-03), 4,4′-diphenyl-4″-(4;2′-binaphthyl-1-yl)triphenylamine (abbreviation: BBAβNαNB), 4,4′-diphenyl-4″-(5;2′-binaphthyl-1-yl)triphenylamine (abbreviation: BBAβNαNB-02), 4-(4-biphenylyl)-4′-(2-naphthyl)-4″-phenyltriphenylamine (abbreviation: TPBiAβNB), 4-(3-biphenylyl)-4′-[4-(2-naphthyl)phenyl]-4″-phenyltriphenylamine (abbreviation: mTPBiAβNBi), 4-(4-biphenylyl)-4′-[4-(2-naphthyl)phenyl]-4″-phenyltriphenylamine (abbreviation: TPBiAβNBi), 4-phenyl-4′-(1-naphthyl)triphenylamine (abbreviation: αNBA1BP), 4,4′-bis(1-naphthyl)triphenylamine (abbreviation: αNBB1BP), 4,4′-diphenyl-4″-[4′-(carbazol-9-yl)biphenyl-4-yl]triphenylamine (abbreviation: YGTBi1BP), 4′-[4-(3-phenyl-9H-carbazol-9-yl)phenyl]tris(biphenyl-4-yl)amine (abbreviation: YGTBi1BP-02), 4-[4′-(carbazol-9-yl)biphenyl-4-yl]-4′-(2-naphthyl)-4″-phenyltriphenylamine (abbreviation: YGTBiPNB), N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-N-[4-(1-naphthyl)phenyl]-9,9′-spirobi[9H-fluoren]-2-amine (abbreviation: PCBNBSF), N,N-bis(biphenyl-4-yl)-9,9′-spirobi[9H-fluoren]-2-amine (abbreviation: BBASF), N,N-bis(biphenyl-4-yl)-9,9′-spirobi[9H-fluoren]-4-amine (abbreviation: BBASF(4)), N-(biphenyl-2-yl)-N-(9,9-dimethyl-9H-fluoren-2-yl)-9,9′-spirobi[9H-fluoren]-4-amine (abbreviation: oFBiSF), N-(biphenyl-4-yl)-N-(9,9-dimethyl-9H-fluoren-2-yl)dibenzofuran-4-amine (abbreviation: FrBiF), N-[4-(1-naphthyl)phenyl]-N-[3-(6-phenyldibenzofuran-4-yl)phenyl]-1-naphthylamine (abbreviation: mPDBfBNBN), 4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP), 4-phenyl-3′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: mBPAFLP), 4-phenyl-4′-[4-(9-phenylfluoren-9-yl)phenyl]triphenylamine (abbreviation: BPAFLBi), 4-phenyl-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBA1BP), 4,4′-diphenyl-4″-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBBi1BP), 4-(1-naphthyl)-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBANB), 4,4′-di(1-naphthyl)-4″-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBNBB), N-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9′-spirobi[9H-fluoren]-2-amine (abbreviation: PCBASF), N-(biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H-fluoren-2-amine (abbreviation: PCBBiF), N,N-bis(9,9-dimethyl-9H-fluoren-2-yl)-9,9′-spirobi-9H-fluoren-4-amine, N,N-bis(9,9-dimethyl-9H-fluoren-2-yl)-9,9′-spirobi-9H-fluoren-3-amine, N,N-bis(9,9-dimethyl-9H-fluoren-2-yl)-9,9′-spirobi-9H-fluoren-2-amine, and N,N-bis(9,9-dimethyl-9H-fluoren-2-yl)-9,9′-spirobi-9H-fluoren-1-amine.
Examples of the aromatic amine compounds that can be used as the material having a hole-transport property include N,N-di(p-tolyl)-N,N-diphenyl-p-phenylenediamine (abbreviation: DTDPPA), 4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (abbreviation: DPAB), 4,4′-bis(N-{4-[N-(3-methylphenyl)-N-phenylamino]phenyl}-N-phenylamino)biphenyl (abbreviation: DNTPD), and 1,3,5-tris[N-(4-diphenylaminophenyl)-N-phenylamino]benzene (abbreviation: DPA3B).
The formation of the hole-injection layer 111 can improve the hole-injection property, which allows the light-emitting device to be driven at a low voltage.
Among substances having an electron-acceptor property, the organic compound having an electron-acceptor property is easy to use because it is easily deposited by vapor deposition.
The hole-transport layer 112 is formed using an organic compound having a hole-transport property. The organic compound having a hole-transport property preferably has a hole mobility of 1×10−6 cm2/Vs or higher.
Examples of the material having a hole-transport property include compounds having an aromatic amine skeleton, such as 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB), N,N-diphenyl-N,N-bis(3-methylphenyl)-4,4′-diaminobiphenyl (abbreviation: TPD), N,N-bis(9,9′-spirobi[9H-fluoren]-2-yl)-N,N-diphenyl-4,4′-diaminobiphenyl (abbreviation: BSPB), 4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP), 4-phenyl-3′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: mBPAFLP), 4-phenyl-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBA1BP), 4,4′-diphenyl-4″-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBBi1BP), 4-(1-naphthyl)-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBANB), 4,4′-di(1-naphthyl)-4″-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBNBB), 9,9-dimethyl-N-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]fluoren-2-amine (abbreviation: PCBAF), and N-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9′-spirobi[9H-fluoren]-2-amine (abbreviation: PCBASF); compounds having a carbazole skeleton, such as 1,3-bis(N-carbazolyl)benzene (abbreviation: mCP), 4,4′-di(N-carbazolyl)biphenyl (abbreviation: CBP), 3,6-bis(3,5-diphenylphenyl)-9-phenylcarbazole (abbreviation: CzTP), 9,9′-diphenyl-9H,9′H-3,3′-bicarbazole (abbreviation: PCCP), 9,9′-bis(biphenyl-4-yl)-3,3′-bi-9H-carbazole (abbreviation: BisBPCz), 9,9′-bis(biphenyl-3-yl)-3,3′-bi-9H-carbazole (abbreviation: BismBPCz), 9-(biphenyl-3-yl)-9′-(biphenyl-4-yl)-9H,9′H-3,3′-bicarbazole (abbreviation: mBPCCBP), 9-(2-naphthyl)-9′-phenyl-9H,9′H-3,3′-bicarbazole (abbreviation: PNCCP), 9-(3-biphenyl)-9′-(2-naphthyl)-3,3′-bi-9H-carbazole (abbreviation: PNCCmBP), 9-(4-biphenyl)-9′-(2-naphthyl)-3,3′-bi-9H-carbazole (abbreviation: PNCCBP), 9,9′-di-2-naphthyl-3,3′-9H,9′H-bicarbazole (abbreviation: BisPNCz), 9-(2-naphthyl)-9′-[1,1′:4′,1″-terphenyl]-3-yl-3,3′-9H,9′H-bicarbazole, 9-(2-naphthyl)-9′-[1,1′: 3′,1″-terphenyl]-3-yl-3,3′-9H,9′H-bicarbazole, 9-(2-naphthyl)-9′-[1,1′: 3′,1″-terphenyl]-5′-yl-3,3′-9H,9′H-bicarbazole, 9-(2-naphthyl)-9′-[1,1′:4′,1″-terphenyl]-4-yl-3,3′-9H,9′H-bicarbazole, 9-(2-naphthyl)-9′-[1,1′: 3′,1″-terphenyl]-4-yl-3,3′-9H,9′H-bicarbazole, 9-(2-naphthyl)-9′-(triphenylen-2-yl)-3,3′-9H,9′H-bicarbazole, 9-phenyl-9′-(triphenylen-2-yl)-3,3′-9H,9′H-bicarbazole (abbreviation: PCCzTp), 9,9′-bis(triphenylen-2-yl)-3,3′-9H,9′H-bicarbazole, 9-(4-biphenyl)-9′-(triphenylen-2-yl)-3,3′-9H,9′H-bicarbazole, 9-(triphenylen-2-yl)-9′-[1,1′: 3′,1″-terphenyl]-4-yl-3,3′-9H,9′H-bicarbazole, and 9-[4-(9-phenyl-9H-carbazol-3-yl)-phenyl]phenanthrene (abbreviation: PCPPn); compounds having a thiophene skeleton, such as 4,4′,4″-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation: DBT3P-II), 2,8-diphenyl-4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]dibenzothiophene (abbreviation: DBTFLP-III), and 4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-6-phenyldibenzothiophene (abbreviation: DBTFLP-IV); and compounds having a furan skeleton, such as 4,4′,4″-(benzene-1,3,5-triyl)tri(dibenzofuran) (abbreviation: DBF3P-II) and 4-{3-[3-(9-phenyl-9H-fluoren-9-yl)phenyl]phenyl}dibenzofuran (abbreviation: mmDBFFLBi-II). Among the above materials, the compound having an aromatic amine skeleton and the compound having a carbazole skeleton are preferable because these compounds are highly reliable and have high hole-transport properties to contribute to a reduction in driving voltage. Note that any of the substances given as examples of the material having a hole-transport property used for the composite material for the hole-injection layer 111 can also be suitably used as the material contained in the hole-transport layer 112.
The light-emitting layer 113 is a layer including a light-emitting substance and preferably includes a light-emitting substance and a host material. The light-emitting layer 113 may additionally include other materials. Alternatively, the light-emitting layer 113 may be a stack of two layers with different compositions.
As the light-emitting substance, fluorescent substances, phosphorescent substances, substances exhibiting thermally activated delayed fluorescence (TADF), or other light-emitting substances may be used.
Examples of the material that can be used as a fluorescent substance in the light-emitting layer are as follows. Other fluorescent substances can also be used.
The examples include 5,6-bis[4-(10-phenyl-9-anthryl)phenyl]-2,2′-bipyridine (abbreviation: PAP2BPy), 5,6-bis[4′-(10-phenyl-9-anthryl)biphenyl-4-yl]-2,2′-bipyridine (abbreviation: PAPP2BPy), N,N′-diphenyl-N,N′-bis[4-(9-phenyl-9H-fluoren-9-yl)phenyl]pyrene-1,6-diamine (abbreviation: 1,6FLPAPrn), N,N′-bis(3-methylphenyl)-N,N′-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]pyrene-1,6-diamine (abbreviation: 1,6mMemFLPAPrn), N,N-bis[4-(9H-carbazol-9-yl)phenyl]-N,N′-diphenylstilbene-4,4′-diamine (abbreviation: YGA2S), 4-(9H-carbazol-9-yl)-4′-(10-phenyl-9-anthryl)triphenylamine (abbreviation: YGAPA), 4-(9H-carbazol-9-yl)-4′-(9,10-diphenyl-2-anthryl)triphenylamine (abbreviation: 2YGAPPA), N,9-diphenyl-N-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazol-3-amine (abbreviation: PCAPA), perylene, 2,5,8,11-tetra-tert-butylperylene (abbreviation: TBP), 4-(10-phenyl-9-anthryl)-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBAPA), N,N″-(2-tert-butylanthracene-9,10-diyldi-4,1-phenylene)bis(N,N′,N-triphenyl-1,4-phenylenediamine) (abbreviation: DPABPA), N,9-diphenyl-N-[4-(9,10-diphenyl-2-anthryl)phenyl]-9H-carbazol-3-amine (abbreviation: 2PCAPPA), N-[4-(9,10-diphenyl-2-anthryl)phenyl]-N,N′,N′-triphenyl-1,4-phenylenediamine (abbreviation: 2DPAPPA), N,N,N′,N′,N″,N″,N″′,N″′-octaphenyldibenzo[g,p]chrysene-2,7,10,15-tetraamine (abbreviation: DBC1), coumarin 30, N-(9,10-diphenyl-2-anthryl)-N,9-diphenyl-9H-carbazol-3-amine (abbreviation: 2PCAPA), N-[9,10-bis(biphenyl-2-yl)-2-anthryl]-N,9-diphenyl-9H-carbazol-3-amine (abbreviation: 2PCABPhA), N-(9,10-diphenyl-2-anthryl)-N,N′,N′-triphenyl-1,4-phenylenediamine (abbreviation: 2DPAPA), N-[9,10-bis(biphenyl-2-yl)-2-anthryl]-N,N′,N′-triphenyl-1,4-phenylenediamine (abbreviation: 2DPABPhA), 9,10-bis(biphenyl-2-yl)-N-[4-(9H-carbazol-9-yl)phenyl]-N-phenylanthracen-2-amine (abbreviation: 2YGABPhA), N,N,9-triphenylanthracen-9-amine (abbreviation: DPhAPhA), coumarin 545T, N,N′-diphenylquinacridone (abbreviation: DPQd), rubrene, 5,12-bis(biphenyl-4-yl)-6,11-diphenyltetracene (abbreviation: BPT), 2-(2-{2-[4-(dimethylamino)phenyl]ethenyl}-6-methyl-4H-pyran-4-ylidene)propanedinitrile (abbreviation: DCM1), 2-{2-methyl-6-[2-(2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile (abbreviation: DCM2), N,N,N′,N′-tetrakis(4-methylphenyl)tetracene-5,11-diamine (abbreviation: p-mPhTD), 7,14-diphenyl-N,N,N′,N′-tetrakis(4-methylphenyl)acenaphtho[1,2-a]fluoranthene-3,10-diamine (abbreviation: p-mPhAFD), 2-{2-isopropyl-6-[2-(1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile (abbreviation: DCJTI), 2-{2-tert-butyl-6-[2-(1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile (abbreviation: DCJTB), 2-(2,6-bis{2-[4-(dimethylamino)phenyl]ethenyl}-4H-pyran-4-ylidene)propanedinitrile (abbreviation: BisDCM), 2-{2,6-bis[2-(8-methoxy-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile (abbreviation: BisDCJTM), N,N′-diphenyl-N,N′-(1,6-pyrene-diyl)bis[(6-phenylbenzo[b]naphtho[1,2-d]furan)-8-amine] (abbreviation: 1,6BnfAPrn-03), 3,10-bis[N-(9-phenyl-9H-carbazol-2-yl)-N-phenylamino]naphtho[2,3-b;6,7-b′]bisbenzofuran (abbreviation: 3,10PCA2Nbf(IV)-02), and 3,10-bis[N-(dibenzofuran-3-yl)-N-phenylamino]naphtho[2,3-b;6,7-b′]bisbenzofuran (abbreviation: 3,10FrA2Nbf(IV)-02). Condensed aromatic diamine compounds typified by pyrenediamine compounds such as 1,6FLPAPrn, 1,6mMemFLPAPrn, and 1,6BnfAPrn-03 are particularly preferable because of their high hole-trapping properties, high emission efficiency, or high reliability.
A condensed heteroaromatic compound containing nitrogen and boron, especially a compound having a diaza-boranaphtho-anthracene skeleton, exhibits a narrow emission spectrum, emits blue light with favorable color purity, and can thus be used suitably. Examples of the compound include 5,9-diphenyl-5,9-diaza-13b-boranaphtho[3,2,1-de]anthracene (abbreviation: DABNA1), 9-(biphenyl-3-yl)-N,N,5,11-tetraphenyl-5H,9H-[1,4]benzazaborino[2,3,4-kl]phenazaborin-3-amine (abbreviation: DABNA2), 2,12-di(tert-butyl)-5,9-di(4-tert-butylphenyl)-N,N-diphenyl-5H,9H-[1,4]benzazaborino[2,3,4-kl]phenazaborin-7-amine (abbreviation: DPhA-tBu4DABNA), 2,12-di(tert-butyl)-N,N,5,9-tetra(4-tert-butylphenyl)-5H,9H-[1,4]benzazaborino[2,3,4-kl]phenazaborin-7-amine (abbreviation: tBuDPhA-tBu4DABNA), 2,12-di(tert-butyl)-5,9-di(4-tert-butylphenyl)-7-methyl-5H,9H-[1,4]benzazaborino[2,3,4-kl]phenazaborine (abbreviation: Me-tBu4DABNA), N7,N7,N13,N13,5,9,11,15-octaphenyl-5H,9H,11H,15H-[1,4]benzazaborino[2,3,4-kl][1,4]benzazaborino[4′,3′,2′:4,5][1,4]benzazaborino[3,2-b]phenazaborine-7,13-diamine (abbreviation: v-DABNA), and 2-(4-tert-butylphenyl)benz[5,6]indolo[3,2,1-jk]benzo[b]carbazole (abbreviation: tBuPBibc).
Besides the above compounds, 9,10,11-tris[3,6-bis(1,1-dimethylethyl)-9H-carbazolyl-9-yl]-2,5,15,18-tetrakis(1,1-dimethylethyl)indolo[3,2,1-de]indolo[3′,2′,1′:8,1][1,4]benzazaborino[2,3,4-kl]phenazaborine (abbreviation: BBCz-G), 9,11-bis[3,6-bis(1,1-dimethylethyl)-9H-carbazolyl-9-yl]-2,5,15,18-tetrakis(1,1-dimethylethyl)indolo[3,2,1-de]indolo[3′,2′,1′:8,1][1,4]benzazaborino[2,3,4-kl]phenazaborine (abbreviation: BBCz-Y), or the like can be suitably used.
Examples of the material that can be used when a phosphorescent substance is used as the light-emitting substance in the light-emitting layer are as follows.
The examples include an organometallic iridium complex having a 4H-triazole skeleton, such as tris{2-[5-(2-methylphenyl)-4-(2,6-dimethylphenyl)-4H-1,2,4-triazol-3-yl-κN2]phenyl-κC}iridium(III) (abbreviation: [Ir(mpptz-dmp)3]), and tris(5-methyl-3,4-diphenyl-4H-1,2,4-triazolato)iridium(III) (abbreviation: [Ir(Mptz)3]); an organometallic iridium complex having a 1H-triazole skeleton, such as tris[3-methyl-1-(2-methylphenyl)-5-phenyl-1H-1,2,4-triazolato]iridium(III) (abbreviation: [Ir(Mptz1-mp)3]) and tris(1-methyl-5-phenyl-3-propyl-1H-1,2,4-triazolato)iridium(III) (abbreviation: [Ir(Prptz1-Me)3]); an organometallic iridium complex having an imidazole skeleton, such as fac-tris[1-(2,6-diisopropylphenyl)-2-phenyl-1H-imidazole]iridium(III) (abbreviation: [Ir(iPrpim)3]), tris[3-(2,6-dimethylphenyl)-7-methylimidazo[1,2-f]phenanthridinato]iridium(III) (abbreviation: [Ir(dmpimpt-Me)3]), and tris(2-{1-[2,6-bis(1-methylethyl)phenyl]-1H-imidazol-2-yl-κN3}-4-cyanophenyl-κC) (abbreviation: CNImIr); an organometallic complex having a benzimizazolidene skeleton, such as tris[(6-tert-butyl-3-phenyl-2H-imidazo[4,5-b]pyrazin-1-yl-κC2)phenyl-κC]iridium(III) (abbreviation: [Ir(cb)3]); and an organometallic iridium complex in which a phenylpyridine derivative including an electron-withdrawing group is a ligand, such as bis[2-(4′,6′-difluorophenyl)pyridinato-N,C2′]iridium(III) tetrakis(1-pyrazolyl)borate (abbreviation: FIr6), bis[2-(4′,6′-difluorophenyl)pyridinato-N,C2′]iridium(III) picolinate (abbreviation: FIrpic), bis{2-[3′,5′-bis(trifluoromethyl)phenyl]pyridinato-N,C2′}iridium(III) picolinate (abbreviation: [Ir(CF3ppy)2(pic)]), and bis[2-(4′,6′-difluorophenyl)pyridinato-N,C2′]iridium(III) acetylacetonate (abbreviation: FIracac). These compounds emit blue phosphorescent light and have an emission peak in the wavelength range of 450 nm to 520 nm.
Other examples include organometallic iridium complexes having a pyrimidine skeleton, such as tris(4-methyl-6-phenylpyrimidinato)iridium(III) (abbreviation: [Ir(mppm)3]), tris(4-t-butyl-6-phenylpyrimidinato)iridium(III) (abbreviation: [Ir(tBuppm)3]), (acetylacetonato)bis(6-methyl-4-phenylpyrimidinato)iridium(III) (abbreviation: [Ir(mppm)2(acac)]), (acetylacetonato)bis(6-tert-butyl-4-phenylpyrimidinato)iridium(III) (abbreviation: [Ir(tBuppm)2(acac)]), (acetylacetonato)bis[6-(2-norbornyl)-4-phenylpyrimidinato]iridium(III) (abbreviation: [Ir(nbppm)2(acac)]), (acetylacetonato)bis[5-methyl-6-(2-methylphenyl)-4-phenylpyrimidinato]iridium(III) (abbreviation: [Ir(mpmppm)2(acac)]), and (acetylacetonato)bis(4,6-diphenylpyrimidinato)iridium(III) (abbreviation: [Ir(dppm)2(acac)]); organometallic iridium complexes having a pyrazine skeleton, such as (acetylacetonato)bis(3,5-dimethyl-2-phenylpyrazinato)iridium(III) (abbreviation: [Ir(mppr-Me)2(acac)]) and (acetylacetonato)bis(5-isopropyl-3-methyl-2-phenylpyrazinato)iridium(III) (abbreviation: [Ir(mppr-iPr)2(acac)]); organometallic iridium complexes having a pyridine skeleton, such as tris(2-phenylpyridinato-N,C2′)iridium(III) (abbreviation: [Jr(ppy)3]), bis(2-phenylpyridinato-N,C2′)iridium(III) acetylacetonate (abbreviation: [Jr(ppy)2(acac)]), bis(benzo[h]quinolinato)iridium(III) acetylacetonate (abbreviation: [Ir(bzq)2(acac)]), tris(benzo[h]quinolinato)iridium(III) (abbreviation: [Jr(bzq)3]), tris(2-phenylquinolinato-N,C2′)iridium(III) (abbreviation: [Ir(pq)3]), bis(2-phenylquinolinato-N,C2′)iridium(III) acetylacetonate (abbreviation: [Ir(pq)2(acac)]), [2-d3-methyl-8-(2-pyridinyl-κN)benzofuro[2,3-b]pyridine-κC]bis[2-(5-d3-methyl-2-pyridinyl-κN2)phenyl-κC]iridium(III) (abbreviation: Ir(5mppy-d3)2(mbfpypy-d3)), [2-d3-methyl-(2-pyridinyl-κN)benzofuro[2,3-b]pyridine-κC]bis[2-(2-pyridinyl-κN)phenyl-κC]iridium(III) (abbreviation: [Ir(ppy)2(mbfpypy-d3)]), [2-(4-d3-methyl-5-phenyl-2-pyridinyl-κN2)phenyl-κC]bis[2-(5-d3-methyl-2-pyridinyl-κN2)phenyl-κC]iridium(III) (abbreviation: [Ir(5mppy-d3)2(mdppy-d3)]), [2-methyl-(2-pyridinyl-κN)benzofuro[2,3-b]pyridine-κC]bis[2-(2-pyridinyl-κN)phenyl-KC]iridium(III) (abbreviation: [Ir(ppy)2(mbfpypy)]), and [2-(4-methyl-5-phenyl-2-pyridinyl-κN)phenyl-κC]bis[2-(2-pyridinyl-κN)phenyl-κC]iridium(III) (abbreviation: [Ir(ppy)2(mdppy)]); and a rare earth metal complex such as tris(acetylacetonato) (monophenanthroline)terbium(III) (abbreviation: [Tb(acac)3(Phen)]). These compounds mainly emit green phosphorescent light and have an emission peak in the wavelength range of 500 nm to 600 nm. Note that organometallic iridium complexes including a pyrimidine skeleton have distinctively high reliability or emission efficiency and thus are particularly preferable.
Other examples include organometallic iridium complexes having a pyrimidine skeleton, such as (diisobutyrylmethanato)bis[4,6-bis(3-methylphenyl)pyrimidinato]iridium(III) (abbreviation: [Ir(5mdppm)2(dibm)]), bis[4,6-bis(3-methylphenyl)pyrimidinato](dipivaloylmethanato)iridium(III) (abbreviation: [Ir(5mdppm)2(dpm)]), and bis[4,6-di(naphthalen-1-yl)pyrimidinato](dipivaloylmethanato)iridium(III) (abbreviation: [Ir(d1npm)2(dpm)]); organometallic iridium complexes having a pyrazine skeleton, such as (acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium(III) (abbreviation: [Ir(tppr)2(acac)]), bis(2,3,5-triphenylpyrazinato)(dipivaloylmethanato)iridium(III) (abbreviation: [Ir(tppr)2(dpm)]), and (acetylacetonato)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III) (abbreviation: [Ir(Fdpq)2(acac)]); organometallic iridium complexes having a pyridine skeleton, such as tris(1-phenylisoquinolinato-N,C2′)iridium(III) (abbreviation: [Ir(piq)3]), bis(1-phenylisoquinolinato-N,C2′)iridium(III) acetylacetonate (abbreviation: [Ir(piq)2(acac)]), (3,7-diethyl-4,6-nonanedionato-κO4,κO6)bis[2,4-dimethyl-6-[7-(1-methylethyl)-1-isoquinolinyl-N]phenyl-κC]iridium(III), and (3,7-diethyl-4,6-nonanedionato-κO4,κO6)bis[2,4-dimethyl-6-[5-(1-methylethyl)-2-quinolinyl-xN]phenyl-κC]iridium(III); platinum complexes such as 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrinplatinum(II) (abbreviation: PtOEP); and rare earth metal complexes such as tris(1,3-diphenyl-1,3-propanedionato)(monophenanthroline)europium(III) (abbreviation: [Eu(DBM)3(Phen)]) and tris[1-(2-thenoyl)-3,3,3-trifluoroacetonato](monophenanthroline)europium(III) (abbreviation: [Eu(TTA)3(Phen)]). These compounds emit red phosphorescent light and have an emission peak in the wavelength range of 600 nm to 700 nm. Furthermore, the organometallic iridium complexes having a pyrazine skeleton can provide red light emission with favorable chromaticity.
Besides the above phosphorescent compounds, known phosphorescent compounds may be selected and used.
Examples of the TADF material include a fullerene, a derivative thereof, an acridine, a derivative thereof, and an eosin derivative. Furthermore, a metal-containing porphyrin, such as a porphyrin containing magnesium (Mg), zinc (Zn), cadmium (Cd), tin (Sn), platinum (Pt), indium (In), or palladium (Pd), can be given. Examples of the metal-containing porphyrin include a protoporphyrin-tin fluoride complex (SnF2(Proto IX)), a mesoporphyrin-tin fluoride complex (SnF2(Meso IX)), a hematoporphyrin-tin fluoride complex (SnF2(Hemato IX)), a coproporphyrin tetramethyl ester-tin fluoride complex (SnF2(Copro III-4Me)), an octaethylporphyrin-tin fluoride complex (SnF2(OEP)), an etioporphyrin-tin fluoride complex (SnF2(Etio I)), and an octaethylporphyrin-platinum chloride complex (PtCl2OEP), which are represented by the following structural formulae.
Alternatively, it is possible to use a heterocyclic compound having one or both of a π-electron rich heteroaromatic ring and a π-electron deficient heteroaromatic ring that is represented by the following structural formulae, such as 2-(biphenyl-4-yl)-4,6-bis(12-phenylindolo[2,3-α]carbazol-11-yl)-1,3,5-triazine (abbreviation: PIC-TRZ), 9-(4,6-diphenyl-1,3,5-triazin-2-yl)-9′-phenyl-9H,9′H-3,3′-bicarbazole (abbreviation: PCCzTzn), 2-{4-[3-(N-phenyl-9H-carbazol-3-yl)-9H-carbazol-9-yl]phenyl}-4,6-diphenyl-1,3,5-triazine (abbreviation: PCCzPTzn), 2-[4-(10H-phenoxazin-10-yl)phenyl]-4,6-diphenyl-1,3,5-triazine (abbreviation: PXZ-TRZ), 3-[4-(5-phenyl-5,10-dihydrophenazin-10-yl)phenyl]-4,5-diphenyl-1,2,4-triazole (abbreviation: PPZ-3TPT), 3-(9,9-dimethyl-9H-acridin-10-yl)-9H-xanthen-9-one (abbreviation: ACRXTN), bis[4-(9,9-dimethyl-9,10-dihydroacridine)phenyl]sulfone (abbreviation: DMAC-DPS), or 10-phenyl-10H,10′H-spiro[acridin-9,9′-anthracen]-10′-one (abbreviation: ACRSA). Such a heterocyclic compound is preferable because of having high electron-transport and hole-transport properties owing to a π-electron rich heteroaromatic ring and a π-electron deficient heteroaromatic ring. Among skeletons having the π-electron deficient heteroaromatic ring, a pyridine skeleton, a diazine skeleton (a pyrimidine skeleton, a pyrazine skeleton, and a pyridazine skeleton), and a triazine skeleton are preferable because of their high stability and reliability. In particular, a benzofuropyrimidine skeleton, a benzothienopyrimidine skeleton, a benzofuropyrazine skeleton, and a benzothienopyrazine skeleton are preferable because of their high electron-acceptor properties and high reliability. Among skeletons having the π-electron rich heteroaromatic ring, an acridine skeleton, a phenoxazine skeleton, a phenothiazine skeleton, a furan skeleton, a thiophene skeleton, and a pyrrole skeleton have high stability and reliability; thus, at least one of these skeletons is preferably included. A dibenzofuran skeleton is preferable as a furan skeleton, and a dibenzothiophene skeleton is preferable as a thiophene skeleton. As a pyrrole skeleton, an indole skeleton, a carbazole skeleton, an indolocarbazole skeleton, a bicarbazole skeleton, and a 3-(9-phenyl-9H-carbazol-3-yl)-9H-carbazole skeleton are particularly preferable. Note that a substance in which the π-electron rich heteroaromatic ring is directly bonded to the π-electron deficient heteroaromatic ring is particularly preferable because the electron-donor property of the π-electron rich heteroaromatic ring and the electron-acceptor property of the π-electron deficient heteroaromatic ring are both improved, the energy difference between the S1 level and the T1 level becomes small, and thus thermally activated delayed fluorescence can be obtained with high efficiency. Note that an aromatic ring to which an electron-withdrawing group such as a cyano group is bonded may be used instead of the π-electron deficient heteroaromatic ring. As a π-electron rich skeleton, an aromatic amine skeleton, a phenazine skeleton, or the like can be used. As a π-electron deficient skeleton, a xanthene skeleton, a thioxanthene dioxide skeleton, an oxadiazole skeleton, a triazole skeleton, an imidazole skeleton, an anthraquinone skeleton, a skeleton containing boron such as phenylborane or boranthrene, an aromatic ring or a heteroaromatic ring having a cyano group or a nitrile group such as benzonitrile or cyanobenzene, a carbonyl skeleton such as benzophenone, a phosphine oxide skeleton, a sulfone skeleton, or the like can be used. As described above, a π-electron deficient skeleton and a π-electron rich skeleton can be used instead of at least one of the π-electron deficient heteroaromatic ring and the π-electron rich heteroaromatic ring.
Note that a TADF material is a material having a small difference between the S1 level and the T1 level and a function of converting triplet excitation energy into singlet excitation energy by reverse intersystem crossing. Thus, a TADF material can upconvert triplet excitation energy into singlet excitation energy (i.e., reverse intersystem crossing) using a small amount of thermal energy and efficiently generate a singlet excited state. In addition, the triplet excitation energy can be converted into light emission.
An exciplex whose excited state is formed of two kinds of substances has an extremely small difference between the S1 level and the T1 level and functions as a TADF material capable of converting triplet excitation energy into singlet excitation energy.
A phosphorescent spectrum observed at a low temperature (e.g., 77 K to 10 K) is used for an index of the T1 level. When the level of energy with a wavelength of the line obtained by extrapolating a tangent to the fluorescent spectrum at a tail on the short wavelength side is the S1 level and the level of energy with a wavelength of the line obtained by extrapolating a tangent to the phosphorescent spectrum at a tail on the short wavelength side is the T1 level, the difference between the S1 level and the T1 level of the TADF material is preferably smaller than or equal to 0.3 eV, further preferably smaller than or equal to 0.2 eV.
When a TADF material is used as the light-emitting substance, the S1 level of the host material is preferably higher than that of the TADF material. In addition, the T1 level of the host material is preferably higher than that of the TADF material.
As the host material in the light-emitting layer, various carrier-transport materials such as materials having an electron-transport property and/or materials having a hole-transport property, and the TADF materials can be used.
The material with a hole-transport property is preferably an organic compound having an amine skeleton or a π-electron rich heteroaromatic ring skeleton, for example. As the π-electron rich heteroaromatic ring, a condensed aromatic ring having at least one of an acridine skeleton, a phenoxazine skeleton, a phenothiazine skeleton, a furan skeleton, a thiophene skeleton, and a pyrrole skeleton is preferable; specifically, a carbazole ring, a dibenzothiophene ring, or a ring in which an aromatic ring or a heteroaromatic ring is further condensed to a carbazole ring or a dibenzothiophene ring is preferable.
Such an organic compound having a hole-transport property further preferably has any of a carbazole skeleton, a dibenzofuran skeleton, a dibenzothiophene skeleton, and an anthracene skeleton. In particular, an aromatic amine having a substituent that has a dibenzofuran ring or a dibenzothiophene ring, an aromatic monoamine that has a naphthalene ring, or an aromatic monoamine in which a 9-fluorenyl group is bonded to nitrogen of an amine through an arylene group may be used. Note that the organic compound having a hole-transport property preferably has an N,N-bis(4-biphenyl)amino group to enable fabricating a light-emitting device with a long lifetime.
Examples of such an organic compound include compounds having an aromatic amine skeleton, such as 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB), N,N-diphenyl-N,N-bis(3-methylphenyl)-4,4′-diaminobiphenyl (abbreviation: TPD), N,N-bis(9,9′-spirobi[9H-fluoren]-2-yl)-N,N-diphenyl-4,4′-diaminobiphenyl (abbreviation: BSPB), 4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP), 4-phenyl-3′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: mBPAFLP), 4-phenyl-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBA1BP), 4,4′-diphenyl-4″-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBBi1BP), 4-(1-naphthyl)-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBANB), 4,4′-di(1-naphthyl)-4″-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBNBB), 9,9-dimethyl-N-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]fluoren-2-amine (abbreviation: PCBAF), and N-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9′-spirobi[9H-fluoren]-2-amine (abbreviation: PCBASF); compounds having a carbazole skeleton, such as 1,3-bis(N-carbazolyl)benzene (abbreviation: mCP), 4,4′-di(N-carbazolyl)biphenyl (abbreviation: CBP), 3,6-bis(3,5-diphenylphenyl)-9-phenylcarbazole (abbreviation: CzTP), and 9,9′-diphenyl-9H,9′H-3,3′-bicarbazole (abbreviation: PCCP); compounds having a thiophene skeleton, such as 4,4′,4″-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation: DBT3P-II), 2,8-diphenyl-4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]dibenzothiophene (abbreviation: DBTFLP-III), and 4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-6-phenyldibenzothiophene (abbreviation: DBTFLP-IV); and compounds having a furan skeleton, such as 4,4′,4″-(benzene-1,3,5-triyl)tri(dibenzofuran) (abbreviation: DBF3P-II) and 4-{3-[3-(9-phenyl-9H-fluoren-9-yl)phenyl]phenyl}dibenzofuran (abbreviation: mmDBFFLBi-II). Among the above materials, the compound having an aromatic amine skeleton and the compound having a carbazole skeleton are preferable because these compounds are highly reliable and have high hole-transport properties to contribute to a reduction in driving voltage. In addition, the organic compounds given as examples of the material having a hole-transport property that can be used for the hole-transport layer can also be used.
As the material having an electron-transport property, for example, a metal complex such as bis(10-hydroxybenzo[h]quinolinato)beryllium(II) (abbreviation: BeBq2), bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum(III) (abbreviation: BAlq), bis(8-quinolinolato)zinc(II) (abbreviation: Znq), bis[2-(2-benzoxazolyl)phenolato]zinc(II) (abbreviation: ZnPBO), or bis[2-(2-benzothiazolyl)phenolato]zinc(II) (abbreviation: ZnBTZ); or an organic compound having a π-electron deficient heteroaromatic ring is preferably used. Examples of the organic compound having a π-electron deficient heteroaromatic ring skeleton include an organic compound that has a heteroaromatic ring having an azole skeleton, an organic compound that has a heteroaromatic ring having a pyridine skeleton, an organic compound that has a heteroaromatic ring having a diazine skeleton, and an organic compound that has a heteroaromatic ring having a triazine skeleton.
Among the above materials, the organic compound that has a heteroaromatic ring having a diazine skeleton (a pyrimidine skeleton, a pyrazine skeleton, or a pyridazine skeleton), the organic compound that has a heteroaromatic ring having a pyridine skeleton, and the organic compound that has a heteroaromatic ring having a triazine skeleton have high reliability and thus are preferable. In particular, the organic compound that has a heteroaromatic ring having a diazine (pyrimidine or pyrazine) skeleton and the organic compound that has a heteroaromatic ring having a triazine skeleton have a high electron-transport property to contribute to a reduction in driving voltage. A benzofuropyrimidine skeleton, a benzothienopyrimidine skeleton, a benzofuropyrazine skeleton, and a benzothienopyrazine skeleton are preferable because of their high electron-acceptor property and high reliability.
Examples of the organic compound having a π-electron deficient heteroaromatic ring skeleton include an organic compound having an azole skeleton, such as 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation: PBD), 3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole (abbreviation: TAZ), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene (abbreviation: OXD-7), 9-[4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl]-9H-carbazole (abbreviation: COl1), 2,2′,2″-(1,3,5-benzenetriyl)tris(1-phenyl-1H-benzimidazole) (abbreviation: TPBI), 2-[3-(dibenzothiophen-4-yl)phenyl]-1-phenyl-1H-benzimidazole (abbreviation: mDBTBIm-II), or 4,4′-bis(5-methylbenzoxazol-2-yl)stilbene (abbreviation: BzOS); an organic compound having a heteroaromatic ring having a pyridine skeleton, such as 3,5-bis[3-(9H-carbazol-9-yl)phenyl]pyridine (abbreviation: 35DCzPPy), 1,3,5-tri[3-(3-pyridyl)phenyl]benzene (abbreviation: TmPyPB), bathophenanthroline (abbreviation: BPhen), bathocuproine (abbreviation: BCP), 2,9-di(naphthalene-2-yl)-4,7-diphenyl-1,10-phenanthroline (abbreviation: NBPhen), 2,2′-(1,3-phenylene)bis(9-phenyl-1,10-phenanthroline) (abbreviation: mPPhen2P), 2-[3-(2-triphenylenyl)phenyl]-1,10-phenanthroline (abbreviation: mTpPPhen), 2-phenyl-9-(2-triphenylenyl)-1,10-phenanthroline (abbreviation: Ph-TpPhen), 2-[4-(9-phenanthrenyl)-1-naphthalenyl]-1,10-phenanthroline (abbreviation: PnNPhen), or 2-[4-(2-triphenylenyl)phenyl]-1,10-phenanthroline (abbreviation: pTpPPhen); an organic compound having a diazine skeleton, such as 2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTPDBq-II), 2-[3-(3′-dibenzothiophen-4-yl)biphenyl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTBPDBq-II), 2-[3′-(9H-carbazol-9-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline (abbreviation: 2mCzBPDBq), 2-[4′-(9-phenyl-9H-carbazol-3-yl)-3,1′-biphenyl-1-yl]dibenzo[f,h]quinoxaline (abbreviation: 2mpPCBPDBq), 2-[4-(3,6-diphenyl-9H-carbazol-9-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2CzPDBq-III), 7-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 7mDBTPDBq-II), 6-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 6mDBTPDBq-II), 9-[3′-(dibenzothiophen-4-yl)biphenyl-3-yl]naphtho[1′,2′:4,5]furo[2,3-b]pyrazine (abbreviation: 9mDBtBPNfpr), 9-[(3′-(dibenzothiophen-4-yl)biphenyl-4-yl]naphtho[1′,2′:4,5]furo[2,3-b]pyrazine (abbreviation: 9pmDBtBPNfpr), 4,6-bis[3-(phenanthren-9-yl)phenyl]pyrimidine (abbreviation: 4,6mPnP2Pm), 4,6-bis[3-(dibenzothiophen-4-yl)phenyl]pyrimidine (abbreviation: 4,6mDBTP2Pm-II), 4,6-bis[3-(9H-carbazol-9-yl)phenyl]pyrimidine (abbreviation: 4,6mCzP2Pm), 9,9′-[pyrimidine-4,6-diylbis(biphenyl-3,3′-diyl)]bis(9H-carbazole) (abbreviation: 4,6mCzBP2Pm), 8-(biphenyl-4-yl)-4-[3-(dibenzothiophen-4-yl)phenyl]-[1]benzofuro[3,2-d]pyrimidine (abbreviation: 8BP-4mDBtPBfpm), 3,8-bis[3-(dibenzothiophen-4-yl)phenyl]benzofuro[2,3-b]pyrazine (abbreviation: 3,8mDBtP2Bfpr), 4,8-bis[3-(dibenzothiophen-4-yl)phenyl]-[1]benzofuro[3,2-d]pyrimidine (abbreviation: 4,8mDBtP2Bfpm), 8-[3′-(dibenzothiophen-4-yl)(biphenyl-3-yl)]naphtho[1′,2′:4,5]furo[3,2-d]pyrimidine (abbreviation: 8mDBtBPNfpm), 8-[(2,2′-binaphthalen)-6-yl]-4-[3-(dibenzothiophen-4-yl)phenyl]-[1]benzofuro[3,2-d]pyrimidine (abbreviation: 8(βN2)-4mDBtPBfpm), 2,2′-(pyridine-2,6-diyl)bis(4-phenylbenzo[h]quinazoline) (abbreviation: 2,6(P-Bqn)2Py), 2,2′-(pyridine-2,6-diyl)bis{4-[4-(2-naphthyl)phenyl]-6-phenylpyrimidine} (abbreviation: 2,6(NP-PPm)2Py), 6-(biphenyl-3-yl)-4-[3,5-bis(9H-carbazol-9-yl)phenyl]-2-phenylpyrimidine (abbreviation: 6mBP-4Cz2PPm), 2,6-bis(4-naphthalen-1-ylphenyl)-4-[4-(3-pyridyl)phenyl]pyrimidine (abbreviation: 2,4NP-6PyPPm), 4-[3,5-bis(9H-carbazol-9-yl)phenyl]-2-phenyl-6-(biphenyl-4-yl)pyrimidine (abbreviation: 6BP-4Cz2PPm), or 7-[4-(9-phenyl-9H-carbazol-2-yl)quinazolin-2-yl]-7H-dibenzo[c,g]carbazole (abbreviation: PC-cgDBCzQz); and an organic compound having a heteroaromatic ring having a triazine skeleton, such as 2-(biphenyl-4-yl)-4-phenyl-6-(9,9′-spirobi[9H-fluoren]-2-yl)-1,3,5-triazine (abbreviation: BP-SFTzn), 2-{3-[3-(benzo[b]naphtho[1,2-d]furan-8-yl)phenyl]phenyl}-4,6-diphenyl-1,3,5-triazine (abbreviation: mBnfBPTzn), 2-{3-[3-(benzo[b]naphtho[1,2-d]furan-6-yl)phenyl]phenyl}-4,6-diphenyl-1,3,5-triazine (abbreviation: mBnfBPTzn-02), 2-{4-[3-(N-phenyl-9H-carbazol-3-yl)-9H-carbazol-9-yl]phenyl}-4,6-diphenyl-1,3,5-triazine (abbreviation: PCCzPTzn), 9-[3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl]-9′-phenyl-2,3′-bi-9H-carbazole (abbreviation: mPCCzPTzn-02), 2-[3′-(9,9-dimethyl-9H-fluoren-2-yl)biphenyl-3-yl]-4,6-diphenyl-1,3,5-triazine (abbreviation: mFBPTzn), 5-[3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl]-7,7-dimethyl-5H,7H-indeno[2,1-b]carbazole (abbreviation: mINc(II)PTzn), 2-{3-[3-(dibenzothiophen-4-yl)phenyl]phenyl}-4,6-diphenyl-1,3,5-triazine (abbreviation: mDBtBPTzn), 2,4,6-tris(3′-(pyridin-3-yl)biphenyl-3-yl)-1,3,5-triazine (abbreviation: TmPPPyTz), 2-[3-(2,6-dimethyl-3-pyridinyl)-5-(9-phenanthrenyl)phenyl]-4,6-diphenyl-1,3,5-triazine (abbreviation: mPn-mDMePyPTzn), 11-[4-(biphenyl-4-yl)-6-phenyl-1,3,5-triazin-2-yl]-11,12-dihydro-12-phenylindolo[2,3-α]carbazole (abbreviation: BP-Icz(II)Tzn), 2-[3′-(triphenylen-2-yl)biphenyl-3-yl]-4,6-diphenyl-1,3,5-triazine (abbreviation: mTpBPTzn), 3-[9-(4,6-diphenyl-1,3,5-triazin-2-yl)-2-dibenzofuranyl]-9-phenyl-9H-carbazole (abbreviation: PCDBfTzn), or 2-(biphenyl-3-yl)-4-phenyl-6-{8-[(1,1′:4′,1″-terphenyl)-4-yl]-1-dibenzofuranyl}-1,3,5-triazine (abbreviation: mBP-TPDBfTzn). The organic compound that has a heteroaromatic ring having a diazine skeleton, the organic compound that has a heteroaromatic ring having a pyridine skeleton, and the organic compound that has a heteroaromatic ring having a triazine skeleton are preferable because of their high reliability. In particular, the organic compound that has a heteroaromatic ring having a diazine (pyrimidine or pyrazine) skeleton and the organic compound that has a heteroaromatic ring having a triazine skeleton have a high electron-transport property to contribute to a reduction in driving voltage.
As the TADF material that can be used as the host material, the above materials mentioned as the TADF material can also be used. When the TADF material is used as the host material, triplet excitation energy generated in the TADF material is converted into singlet excitation energy by reverse intersystem crossing and transferred to the light-emitting substance, whereby the emission efficiency of the light-emitting device can be increased. Here, the TADF material functions as an energy donor, and the light-emitting substance functions as an energy acceptor.
This is very effective in the case where the light-emitting substance is a fluorescent substance. In that case, the S1 level of the TADF material is preferably higher than that of the fluorescent substance in order that high emission efficiency can be achieved. Furthermore, the T1 level of the TADF material is preferably higher than the S1 level of the fluorescent substance. Therefore, the T1 level of the TADF material is preferably higher than that of the fluorescent substance.
It is also preferable to use a TADF material that emits light whose wavelength overlaps with the wavelength on a lowest-energy-side absorption band of the fluorescent substance, in which case excitation energy is transferred smoothly from the TADF material to the fluorescent substance and light emission can be obtained efficiently.
In order to efficiently generate singlet excitation energy from the triplet excitation energy by reverse intersystem crossing, carrier recombination preferably occurs in the TADF material. It is also preferable that the triplet excitation energy generated in the TADF material not be transferred to the triplet excitation energy of the fluorescent substance. For that reason, the fluorescent substance preferably has a protective group around a luminophore (a skeleton that brings about light emission) of the fluorescent substance. As the protective group, a substituent having no π bond and a saturated hydrocarbon are preferably used. Specific examples include an alkyl group having 3 to 10 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 10 carbon atoms, and a trialkylsilyl group having 3 to 10 carbon atoms. It is further preferable that the fluorescent substance have a plurality of protective groups. The substituents having no π bond are poor in carrier transport performance, whereby the TADF material and the luminophore of the fluorescent substance can be made away from each other with little influence on carrier transportation or carrier recombination. Here, the luminophore refers to an atomic group (skeleton) that brings about light emission in a fluorescent substance. The luminophore is preferably a skeleton having a π bond, further preferably includes an aromatic ring, and still further preferably includes a condensed aromatic ring or a condensed heteroaromatic ring. Examples of the luminophore include a phenanthrene skeleton, a stilbene skeleton, an acridone skeleton, a phenoxazine skeleton, a phenothiazine skeleton, a naphthalene skeleton, an anthracene skeleton, a fluorene skeleton, a chrysene skeleton, a triphenylene skeleton, a tetracene skeleton, a pyrene skeleton, a perylene skeleton, a coumarin skeleton, a quinacridone skeleton, and a naphthobisbenzofuran skeleton. Specifically, a fluorescent substance having any of a naphthalene skeleton, an anthracene skeleton, a fluorene skeleton, a chrysene skeleton, a triphenylene skeleton, a tetracene skeleton, a pyrene skeleton, a perylene skeleton, a coumarin skeleton, a quinacridone skeleton, and a naphthobisbenzofuran skeleton is preferable because of its high fluorescence quantum yield.
In the case where a fluorescent substance is used as the light-emitting substance, a material having an anthracene skeleton is suitably used as the host material. The use of a substance having an anthracene skeleton as the host material for the fluorescent substance makes it possible to obtain a light-emitting layer with high emission efficiency and high durability. Among the substances having an anthracene skeleton, a substance having a diphenylanthracene skeleton, in particular, a substance having a 9,10-diphenylanthracene skeleton, is chemically stable and thus is preferably used as the host material. The host material preferably has a carbazole skeleton because the hole-injection and hole-transport properties are improved; further preferably, the host material has a benzocarbazole skeleton in which a benzene ring is further condensed to a carbazole skeleton because the HOMO level thereof is shallower than that of the host material having a carbazole skeleton by approximately 0.1 eV and thus holes enter the host material easily. In particular, the host material preferably has a dibenzocarbazole skeleton because the HOMO level thereof is shallower than that of the host material having a carbazole skeleton by approximately 0.1 eV so that holes enter the host material easily, the hole-transport property is improved, and the heat resistance is increased. Accordingly, a substance that has both a 9,10-diphenylanthracene skeleton and a carbazole skeleton (or a benzocarbazole or dibenzocarbazole skeleton) is further preferable as the host material. Note that in terms of the hole-injection and hole-transport properties described above, instead of a carbazole skeleton, a benzofluorene skeleton or a dibenzofluorene skeleton may be used. Examples of such a substance include 9-phenyl-3-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation: PCzPA), 3-[4-(1-naphthyl)phenyl]-9-phenyl-9H-carbazole (abbreviation: PCPN), 9-[4-(10-phenyl-9-anthracenyl)phenyl]-9H-carbazole (abbreviation: CzPA), 7-[4-(10-phenyl-9-anthryl)phenyl]-7H-dibenzo[c,g]carbazole (abbreviation: cgDBCzPA), 6-[3-(9,10-diphenyl-2-anthryl)phenyl]benzo[b]naphtho[1,2-d]furan (abbreviation: 2mBnfPPA), 9-phenyl-10-[4-(9-phenyl-9H-fluoren-9-yl)biphenyl-4′-yl]anthracene (abbreviation: FLPPA), 9-(1-naphthyl)-10-[4-(2-naphthyl)phenyl]anthracene (abbreviation: aN-PNPAnth), 9-(1-naphthyl)-10-(2-naphthyl)anthracene (abbreviation: α,βADN), 2-(10-phenylanthracen-9-yl)dibenzofuran, 2-(10-phenyl-9-anthracenyl)benzo[b]naphtho[2,3-d]furan (abbreviation: Bnf(II)PhA), 9-(2-naphthyl)-10-[3-(2-naphthyl)phenyl]anthracene (abbreviation: PN-mQNPAnth), and 1-{4-[10-(biphenyl-4-yl)-9-anthracenyl]phenyl}-2-ethyl-1H-benzimidazole (abbreviation: EtBImPBPhA). In particular, CzPA, cgDBCzPA, 2mBnfPPA, and PCzPA exhibit excellent properties and thus are preferably selected.
Note that the host material may be a mixture of a plurality of kinds of substances; in the case of using a mixed host material, it is preferable to mix a material having an electron-transport property with a material having a hole-transport property. By mixing the material having an electron-transport property with the material having a hole-transport property, the transport property of the light-emitting layer 113 can be easily adjusted and a recombination region can be easily controlled. The weight ratio of the content of the material having a hole-transport property to the content of the material having an electron-transport property is preferably 1:19 to 19:1.
Note that a phosphorescent substance can be used as part of the mixed material. When a fluorescent substance is used as the light-emitting substance, a phosphorescent substance can be used as an energy donor for supplying excitation energy to the fluorescent substance.
An exciplex may be formed of these mixed materials. These mixed materials are preferably selected so as to form an exciplex that exhibits light emission whose wavelength overlaps with the wavelength on a lowest-energy-side absorption band of the light-emitting substance, in which case energy can be transferred smoothly and light emission can be obtained efficiently. The use of such a structure is preferable because the driving voltage can also be reduced.
Note that at least one of the materials forming an exciplex may be a phosphorescent substance. In this case, triplet excitation energy can be efficiently converted into singlet excitation energy by reverse intersystem crossing.
In order to form an exciplex efficiently, a material having an electron-transport property is preferably combined with a material having a hole-transport property and a HOMO level higher than or equal to that of the material having an electron-transport property. In addition, the LUMO level of the material having a hole-transport property is preferably higher than or equal to that of the material having an electron-transport property. Note that the LUMO levels and the HOMO levels of the materials can be derived from the electrochemical characteristics (the reduction potentials and the oxidation potentials) of the materials that are measured by cyclic voltammetry (CV).
The formation of an exciplex can be confirmed by a phenomenon in which the emission spectrum of the mixed film in which the material having a hole-transport property and the material having an electron-transport property are mixed is shifted to the longer wavelength side than the emission spectrum of each of the materials (or has another peak on the longer wavelength side) observed by comparison of the emission spectra of the material having a hole-transport property, the material having an electron-transport property, and the mixed film of these materials, for example. Alternatively, the formation of an exciplex can be confirmed by a difference in transient response, such as a phenomenon in which the transient photoluminescence (PL) lifetime of the mixed film has longer lifetime components or has a larger proportion of delayed components than that of each of the materials, observed by comparison of transient PL of the material having a hole-transport property, the material having an electron-transport property, and the mixed film of these materials. The transient PL can be rephrased as transient electroluminescence (EL). That is, the formation of an exciplex can also be confirmed by a difference in transient response observed by comparison of the transient EL of the material having a hole-transport property, the material having an electron-transport property, and the mixed film of these materials.
The first electron-transport layer 114_1 and the second electron-transport layer 114_2 each contain a material having an electron-transport property. The material having an electron-transport property preferably has an electron mobility higher than or equal to 1×10−7 cm2/Vs, further preferably higher than or equal to 1×10−6 cm2/Vs in the case where the square root of the electric field strength [V/cm] is 600. Note that any other substance can also be used as long as the substance has an electron-transport property higher than a hole-transport property. An organic compound including a π-electron deficient heteroaromatic ring is preferable as the above organic compound. The organic compound including a π-electron deficient heteroaromatic ring is preferably one or more of an organic compound including a heteroaromatic ring having an azole skeleton, an organic compound including a heteroaromatic ring having a pyridine skeleton, an organic compound including a heteroaromatic ring having a diazine skeleton, and an organic compound including a heteroaromatic ring having a triazine skeleton.
As the organic compounds having an electron-transport property that can be used in the first electron-transport layer 114_1 and the second electron-transport layer 114_2, any of the aforementioned organic compounds that can be used as the organic compound having an electron-transport property in the first light-emitting layer 113_1 and the second light-emitting layer 113_2 can be used. Among the above-described materials, the organic compound that has a heteroaromatic ring having a diazine skeleton, the organic compound that has a heteroaromatic ring having a pyridine skeleton, and the organic compound that has a heteroaromatic ring having a triazine skeleton are especially preferable because of having high reliability. In particular, the organic compound that has a heteroaromatic ring having a diazine (pyrimidine or pyrazine) skeleton and the organic compound that has a heteroaromatic ring having a triazine skeleton have a high electron-transport property to contribute to a reduction in driving voltage. An organic compound having a phenanthroline ring such as mTpPPhen, PnNPhen, or mPPhen2P is especially preferable, and an organic compound having a phenanthroline dimer structure such as mPPhen2P is further preferable because of its excellent stability.
The first electron-transport layer preferably includes an organic compound having an electron-transport property with an acid dissociation constant pKa of 4 or less.
The first electron-transport layer 114_1 and the second electron-transport layer 1142 may have a stacked-layer structure. In the case where the first electron-transport layer 1141 has a stacked-layer structure, all the stacked layers preferably have the structure as described in Embodiment 1. In the case where the second electron-transport layer 1142 has a stacked-layer structure, the layer in contact with the second light-emitting layer 113_2 may function as a hole-block layer. In the case where the electron-transport layer in contact with the light-emitting layer functions as a hole-block layer, the electron-transport layer is preferably formed using a material having a deeper HOMO level than a material included in the light-emitting layer by more than or equal to 0.5 eV.
A layer containing an alkali metal, an alkaline earth metal, or a compound thereof such as lithium oxide (Li2O), lithium fluoride (LiF), cesium fluoride (CsF), calcium fluoride (CaF2), or 8-hydroxyquinolinato-lithium (Liq) may be provided as the electron-injection layer 115 between the second electron-transport layer 114_2 and the second electrode 102. An electrode or a layer that is formed using a substance having an electron-transport property and includes an alkali metal, an alkaline earth metal, or a compound thereof can be used as the electron-injection layer 115. Examples of the electrode include a substance in which electrons are added at high concentration to calcium oxide-aluminum oxide. Any of the organic compounds given as examples of the organic compound having strong basicity in Embodiment 1 can be used.
The electron-injection layer 115 may be formed using any of the above substances alone, or any of the above substances contained in a layer including a substance having an electron-transport property.
Note that as the electron-injection layer 115, it is possible to use a layer including a substance having an electron-transport property (preferably an organic compound having a bipyridine skeleton) that contains a fluoride of the alkali metal or the alkaline earth metal at a concentration higher than or equal to that at which the electron-injection layer 115 becomes in a microcrystalline state (50 wt % or higher). Since the layer has a low refractive index, a light-emitting device including the layer can have favorable external quantum efficiency.
The second electrode 102 is an electrode including a cathode. The second electrode 102 may have a stacked-layer structure, in which case a layer in contact with the organic compound layer 103 functions as a cathode. For the cathode, a metal, an alloy, an electrically conductive compound, or a mixture thereof each having a low work function (specifically, lower than or equal to 3.8 eV) or the like can be used. Specific examples of such a cathode material include elements belonging to Group 1 or 2 of the periodic table, such as alkali metals (e.g., lithium (Li) or cesium (Cs)), magnesium (Mg), calcium (Ca), and strontium (Sr), alloys containing these elements (e.g., MgAg and AlLi), compounds containing these elements (e.g., lithium fluoride (LiF), cesium fluoride (CsF), and calcium fluoride (CaF2)), rare earth metals such as europium (Eu) and ytterbium (Yb), and alloys containing these rare earth metals. However, when the electron-injection layer 115 or a thin film formed using any of the above materials having a low work function is provided between the second electrode 102 and the electron-transport layer, a variety of conductive materials such as Al, Ag, ITO, or indium oxide-tin oxide containing silicon or silicon oxide can be used for the cathode regardless of the work function.
When the second electrode 102 is formed using a material that transmits visible light, the light-emitting device can emit light from the second electrode 102 side. When the first electrode 101 is formed using a material that transmits visible light, the light-emitting device can emit light from the first electrode 101 side.
Films of these conductive materials can be deposited by a dry process such as a vacuum evaporation method or a sputtering method, an ink-jet method, a spin coating method, or the like. Alternatively, a wet process using a sol-gel method or a wet process using a paste of a metal material may be employed.
The organic compound layer 103 can be formed by any of a variety of methods, including a dry process and a wet process. For example, a vacuum evaporation method, a gravure printing method, an offset printing method, a screen printing method, an ink-jet method, a spin coating method, or the like may be used.
Different deposition methods may be used to form the electrodes or the layers described above.
The light-emitting device having two light-emitting units is described with reference to
When the emission colors of the light-emitting units are different, light emission of a desired color can be obtained from the light-emitting device as a whole. For example, in a light-emitting device having two light-emitting units, the emission colors of the first light-emitting unit may be red and green and the emission color of the second light-emitting unit may be blue, so that the light-emitting device can emit white light as the whole.
The organic compound layer 103, the first light-emitting unit 501, the second light-emitting unit 502, the layers such as the carrier-generation layer, and the electrodes that are described above can be formed by a method such as an evaporation method (including a vacuum evaporation method), a droplet discharge method (also referred to as an ink-jet method), a coating method, or a gravure printing method. A low molecular material, a middle molecular material (including an oligomer and a dendrimer), or a high molecular material may be included in the above components.
The light-emitting device 130c includes an organic compound layer 103c between a first electrode 101c over the insulating layer 175 and the second electrode 102. The organic compound layer 103c has a structure in which a first light-emitting unit 501c and a second light-emitting unit 502c are stacked with an intermediate layer 116c therebetween. Although
The light-emitting device 130d includes an organic compound layer 103d between a first electrode 101d over the insulating layer 175 and the second electrode 102. The organic compound layer 103d has a structure in which a first light-emitting unit 501d and a second light-emitting unit 502d are stacked with an intermediate layer 116d therebetween. Although
In the light-emitting devices 130c and 130d, the intermediate layers 116c and 116d and the first electron-transport layers 114c_1 and 114d_1 preferably have the structures described in Embodiment 1.
Note that each of the electron-injection layer 115 and the second electrode 102 is preferably one continuous layer shared by the light-emitting device 130c and the light-emitting device 130d. The layers other than the electron-injection layer 115 included in the organic compound layer 103c are independent from the layers other than the electron-injection layer 115 included in the organic compound layer 103d because processing with a photolithography technique is performed after the second electron-transport layer 114c_2 is formed and after the second electron-transport layer 114d_2 is formed. End portions (contours) of the layers other than the electron-injection layer 115 in the organic compound layer 103c are processed by a photolithography technique and thus are substantially aligned in the direction perpendicular to the substrate. End portions (contours) of the layers other than the electron-injection layer 115 in the organic compound layer 103d are processed by a photolithography technique and thus are substantially aligned with each other in the direction perpendicular to the substrate.
The space d is present between the organic compound layer 103c and the organic compound layer 103d because of processing with a photolithography technique. Since the organic compound layers are processed by a photolithography technique, the distance between the first electrode 101c and the first electrode 101d can be made small, greater than or equal to 2 μm and less than or equal to 5 μm, compared with the case where mask vapor deposition is performed.
The light-emitting device of one embodiment of the present invention having the above-described structure can have high current efficiency, high reliability, and a suppressed increase in driving voltage.
One embodiment of the present invention is particularly suitably used in a light-emitting device formed through a photolithography process and also contributes to cost reduction in manufacturing of light-emitting devices not formed through a photolithography process because high stability in the atmosphere of one embodiment of the present invention increases yield and eliminates the need for too strictly managing the atmosphere in the manufacturing process.
Described in this embodiment is a mode in which the organic EL device of one embodiment of the present invention is used as a display element of a display apparatus.
As illustrated in
A display apparatus includes a pixel portion 177 in which a plurality of pixels 178 are arranged in matrix. The pixel 178 includes a subpixel 110R, a subpixel 110G, and a subpixel 110B.
In this specification and the like, for example, description common to the subpixels 110R, 110G, and 110B is sometimes made using the collective term “subpixel 110”. As for other components that are distinguished from each other using letters of the alphabet, matters common to the components are sometimes described using reference numerals excluding the letters of the alphabet.
The subpixel 110R emits red light, the subpixel 110G emits green light, and the subpixel 110B emits blue light. Thus, a full-color image can be displayed on the pixel portion 177. Note that in this embodiment, three colors of red (R), green (G), and blue (B) are given as examples of colors of light emitted by the subpixels; however, subpixels of a different combination of colors may be employed. The number of subpixels is not limited to three, and may be four or more. Examples of four subpixels include subpixels emitting light of four colors of R, G, B, and white (W), subpixels emitting light of four colors of R, G, B, and Y, and four subpixels emitting light of R, G, and B and infrared light (IR).
In this specification and the like, the row direction and the column direction are sometimes referred to as the X direction and the Y direction, respectively. The X direction and the Y direction intersect with each other and are perpendicular to each other, for example.
Outside the pixel portion 177, a region 141 is provided and a connection portion 140 may also be provided. The region 141 is provided between the pixel portion 177 and the connection portion 140. The organic compound layer 103 is provided in the region 141. A conductive layer 151C is provided in the connection portion 140.
Although
In the pixel portion 177, the organic EL device 130 is provided over the insulating layer 175 and the plug 176. A protective layer 131 is provided to cover the organic EL device 130. A substrate 120 is bonded to the protective layer 131 with a resin layer 122. An inorganic insulating layer 125 and an insulating layer 127 over the inorganic insulating layer 125 are preferably provided between the adjacent organic EL devices 130.
Although
In
The display apparatus of one embodiment of the present invention can be, for example, a top-emission display apparatus where light is emitted in the direction opposite to a substrate over which organic EL devices are formed. Note that the display apparatus of one embodiment of the present invention may be of a bottom-emission type.
The organic EL device 130R has a structure as described in Embodiments 1 and 2. The organic EL device 130R includes a first electrode 101R (pixel electrode) including a conductive layer 151R and a conductive layer 152R, a first EL layer 104R over the first electrode 101R, an organic compound layer (a second EL layer 105 over the first EL layer 104R), and the second electrode 102 (common electrode) over the second EL layer 105. The second EL layer 105 is preferably positioned closer to the second electrode 102 (common electrode) side than the light-emitting layer is, and is preferably a hole-block layer, a second electron-transport layer, an electron-injection layer, or stacked layers thereof. Such a structure can reduce damage to the light-emitting layer or an active layer during a photolithography process, which promises favorable film quality and electrical characteristics.
The organic EL device 130G has a structure as described in Embodiments 1 and 2. The organic EL device 130G includes a first electrode 101G (pixel electrode) including a conductive layer 151G and a conductive layer 152G, a first EL layer 104G over the first electrode 101G, the second EL layer 105 over the first EL layer 104G, and the second electrode 102 (common electrode) over the second EL layer 105. The second EL layer 105 is preferably a hole-block layer, a second electron-transport layer, an electron-injection layer, or stacked layers thereof.
The organic EL device 130B has a structure as described in Embodiments 1 and 2. The organic EL device 130B includes a first electrode 101B (pixel electrode) including a conductive layer 151B and a conductive layer 152B, a first EL layer 104B over the first electrode 101B, the second EL layer 105 over the first EL layer 104B, and the second electrode 102 (common electrode) over the second EL layer 105. The second EL layer 105 is preferably a hole-block layer, a second electron-transport layer, an electron-injection layer, or stacked layers thereof.
In the organic EL device, one of the pixel electrode (first electrode) and the common electrode (second electrode) functions as an anode and the other functions as a cathode. In this embodiment, description is made on the assumption that the pixel electrode functions as the anode and the common electrode functions as the cathode unless otherwise specified.
The first EL layers 104R, 104G, and 104B are island-shaped layers that are independent of each other for the respective colors. It is preferable that the first EL layers 104R, 104G, and 104B not overlap with one another. Providing the island-shaped first EL layer 104 in each of the organic EL devices 130 can suppress leakage current between the adjacent organic EL devices 130 even in a high-resolution display apparatus. This can prevent crosstalk, so that a display apparatus with extremely high contrast can be obtained. Specifically, a display apparatus having high current efficiency at low luminance can be obtained.
The island-shaped first EL layer 104 can be formed by forming an EL film and processing the EL film by a photolithography technique.
In the display apparatus of one embodiment of the present invention, the first electrode 101 (pixel electrode) of the organic EL device preferably has a stacked-layer structure. For example, in the example illustrated in
A metal material can be used for the conductive layer 151, for example. Specifically, it is possible to use a metal such as aluminum (Al), titanium (Ti), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), gallium (Ga), zinc (Zn), indium (In), tin (Sn), molybdenum (Mo), tantalum (Ta), tungsten (W), palladium (Pd), gold (Au), platinum (Pt), silver (Ag), yttrium (Y), or neodymium (Nd) or an alloy containing an appropriate combination of any of these metals, for example.
For the conductive layer 152, an oxide containing one or more selected from indium, tin, zinc, gallium, titanium, aluminum, and silicon can be used. For example, it is preferable to use a conductive oxide containing one or more of indium oxide, indium tin oxide, indium zinc oxide, zinc oxide, zinc oxide containing gallium, titanium oxide, indium zinc oxide containing gallium, indium zinc oxide containing aluminum, indium tin oxide containing silicon, indium zinc oxide containing silicon, and the like. In particular, indium tin oxide containing silicon can be suitably used for the conductive layer 152 because of having a high work function, for example, a work function higher than or equal to 4.0 eV.
The conductive layer 151 and the conductive layer 152 may each be a stack of a plurality of layers containing different materials. In that case, the conductive layer 151 may include a layer formed using a material that can be used for the conductive layer 152, such as a conductive oxide, and the conductive layer 152 may include a layer formed using a material that can be used for the conductive layer 151, such as a metal material. In the case where the conductive layer 151 is a stack of two or more layers, for example, a layer in contact with the conductive layer 152 can be formed using a material that can be used for the conductive layer 152.
The conductive layer 151 preferably has a tapered end portion. Specifically, the conductive layer 151 preferably has a tapered end portion with a taper angle less than 90°. In that case, the conductive layer 152 provided along the side surface of the conductive layer 151 also has a tapered shape. When the side surface of the conductive layer 152 has a tapered shape, coverage with the first EL layer 104 provided along the side surface of the conductive layer 152 can be improved.
Since the organic EL device 130 has the structure as described in Embodiments 1 and 2, the display apparatus of one embodiment of the present invention can have high moisture resistance, high water resistance, high oxygen resistance, high chemical resistance, a low driving voltage, and high emission efficiency.
Next, an exemplary method for manufacturing the display apparatus having the structure illustrated in
Thin films included in the display apparatus (e.g., insulating films, semiconductor films, and conductive films) can be formed by a sputtering method, a chemical vapor deposition (CVD) method, a vacuum evaporation method, a pulsed laser deposition (PLD) method, an atomic layer deposition (ALD) method, or the like.
Thin films included in the display apparatus (e.g., insulating films, semiconductor films, and conductive films) can also be formed by a wet process such as spin coating, dipping, spray coating, ink-jetting, dispensing, screen printing, offset printing, doctor blade coating, slit coating, roll coating, curtain coating, or knife coating.
Thin films included in the display apparatus can be processed by a photolithography technique, for example.
As light used for exposure in the photolithography technique, for example, light with an i-line (wavelength: 365 nm), light with a g-line (wavelength: 436 nm), light with an h-line (wavelength: 405 nm), or light in which the i-line, the g-line, and the h-line are mixed can be used. Alternatively, ultraviolet rays, KrF laser light, ArF laser light, or the like can be used. Exposure may be performed by liquid immersion exposure technique. As the light for exposure, extreme ultraviolet (EUV) light or X-rays may also be used. Furthermore, instead of the light used for exposure, an electron beam can be used.
For etching of thin films, a dry etching method, a wet etching method, a sandblast method, or the like can be used.
First, as illustrated in
As the substrate, a substrate that has heat resistance high enough to withstand at least heat treatment performed later can be used. For example, it is possible to use a glass substrate; a quartz substrate; a sapphire substrate; a ceramic substrate; an organic resin substrate; or a semiconductor substrate such as a single crystal semiconductor substrate or a polycrystalline semiconductor substrate of silicon, silicon carbide, or the like, a compound semiconductor substrate of silicon germanium or the like, or an SOI substrate.
Next, as illustrated in
Next, as illustrated in
Then, a resist mask 191 is formed over the conductive film 151f as illustrated in
Subsequently, as illustrated in
Next, the resist mask 191 is removed as illustrated in
Then, as illustrated in
As the insulating film 156f, an inorganic insulating film such as an oxide insulating film, a nitride insulating film, an oxynitride insulating film, or a nitride oxide insulating film, e.g., silicon oxynitride, can be used.
Subsequently, as illustrated in
Next, as illustrated in
A conductive oxide can be used for the conductive film 152f, for example. The conductive film 152f may have a stacked-layer structure.
Then, as illustrated in
Next, as illustrated in
Then, as illustrated in
Providing the sacrificial film 158Rf over the organic compound film 103Rf can reduce damage to the organic compound film 103Rf in the manufacturing process of the display apparatus, resulting in an increase in the reliability of the organic EL device.
As the sacrificial film 158Rf, a film that is highly resistant to the process conditions for the organic compound film 103Rf, specifically, a film having high etching selectivity with respect to the organic compound film 103Rf is used. For the mask film 159Rf, a film having high etching selectivity with respect to the sacrificial film 158Rf is used.
The sacrificial film 158Rf and the mask film 159Rf are formed at a temperature lower than the upper temperature limit of the organic compound film 103Rf. The typical substrate temperatures in formation of the sacrificial film 158Rf and the mask film 159Rf are each higher than or equal to 100° C. and lower than or equal to 200° C., preferably higher than or equal to 100° C. and lower than or equal to 150° C., and further preferably higher than or equal to 100° C. and lower than or equal to 120° C.
The sacrificial film 158Rf and the mask film 159Rf are preferably films that can be removed by a wet etching method or a dry etching method.
Note that the sacrificial film 158Rf that is formed over and in contact with the organic compound film 103Rf is preferably formed by a formation method that is less likely to damage the organic compound film 103Rf than a formation method of the mask film 159Rf. For example, the sacrificial film 158Rf is preferably formed by an ALD method or a vacuum evaporation method rather than a sputtering method.
As each of the sacrificial film 158Rf and the mask film 159Rf, one or more of a metal film, an alloy film, a metal oxide film, a semiconductor film, an organic insulating film, and an inorganic insulating film, for example, can be used.
For each of the sacrificial film 158Rf and the mask film 159Rf, a metal material such as gold, silver, platinum, magnesium, nickel, tungsten, chromium, molybdenum, iron, cobalt, copper, palladium, titanium, aluminum, yttrium, zirconium, or tantalum or an alloy material containing any of the metal materials can be used, for example. It is particularly preferable to use a low-melting-point material such as aluminum or silver. It is preferable to use a metal material that can block ultraviolet rays for one or both of the sacrificial film 158Rf and the mask film 159Rf, in which case the organic compound film 103Rf can be inhibited from being irradiated with ultraviolet rays in patterning light exposure, and deterioration of the organic compound film 103Rf can be suppressed.
The sacrificial film 158Rf and the mask film 159Rf can each be formed using a metal oxide such as In—Ga—Zn oxide, indium oxide, In—Zn oxide, In—Sn oxide, indium titanium oxide (In—Ti oxide), indium tin zinc oxide (In—Sn—Zn oxide), indium titanium zinc oxide (In—Ti—Zn oxide), indium gallium tin zinc oxide (In—Ga—Sn—Zn oxide), or indium tin oxide containing silicon.
In the above metal oxide, in place of gallium, an element M (M is one or more of aluminum, silicon, boron, yttrium, copper, vanadium, beryllium, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, and magnesium) may be used.
The sacrificial film 158Rf and the mask film 159Rf are preferably formed using a semiconductor material such as silicon or germanium for excellent compatibility with a semiconductor manufacturing process. Alternatively, a compound containing the above semiconductor material can be used.
As each of the sacrificial film 158Rf and the mask film 159Rf, any of a variety of inorganic insulating films can be used. In particular, an oxide insulating film is preferable because its adhesion to the organic compound film 103Rf is higher than that of a nitride insulating film.
Subsequently, a resist mask 190R is formed as illustrated in
The resist mask 190R is provided at a position overlapping with the conductive layer 152R. The resist mask 190R is preferably provided also at a position overlapping with the conductive layer 152C. This can inhibit the conductive layer 152C from being damaged during the process of manufacturing the display apparatus.
Next, as illustrated in
The use of a wet etching method can reduce damage to the organic compound film 103Rf in processing of the sacrificial film 158Rf and the mask film 159Rf, as compared to the case of using a dry etching method. In the case of using a wet etching method, it is preferable to use a developer, an alkaline aqueous solution such as a tetramethylammonium hydroxide (TMAH) aqueous solution, or an acid aqueous solution such as dilute hydrofluoric acid, oxalic acid, phosphoric acid, acetic acid, nitric acid, or a chemical solution containing a mixed solution of any of these acids, for example.
In the case of using a dry etching method to process the sacrificial film 158Rf, deterioration of the organic compound film 103Rf can be suppressed by not using a gas containing oxygen as the etching gas.
The resist mask 190R can be removed by a method similar to that for the resist mask 191.
Next, as illustrated in
Accordingly, as illustrated in
The organic compound film 103Rf is preferably processed by anisotropic etching. Anisotropic dry etching is particularly preferable. Alternatively, wet etching may be used.
In the case of using a dry etching method, deterioration of the organic compound film 103Rf can be suppressed by not using a gas containing oxygen as the etching gas.
A gas containing oxygen may be used as the etching gas. When the etching gas contains oxygen, the etching rate can be increased. Therefore, the etching can be performed under a low-power condition while an adequately high etching rate is maintained. Accordingly, damage to the organic compound film 103Rf can be reduced. Furthermore, a defect such as attachment of a reaction product generated during the etching can be inhibited.
In the case of using a dry etching method, it is preferable to use a gas containing at least one of H2, CF4, C4F8, SF6, CHF3, Cl2, H2O, BCl3, and a Group 18 element such as He or Ar as the etching gas, for example. Alternatively, a gas containing oxygen and at least one of the above is preferably used as the etching gas. Alternatively, an oxygen gas may be used as the etching gas.
Then, as illustrated in
The organic compound film 103Gf can be formed by a method similar to that for forming the organic compound film 103Rf. The organic compound film 103Gf can have a structure similar to that of the organic compound film 103Rf.
Subsequently, as illustrated in
The resist mask 190G is provided at a position overlapping with the conductive layer 152G.
Subsequently, as illustrated in
Then, an organic compound film 103Bf is formed as illustrated in
The organic compound film 103Bf can be formed by a method similar to that for forming the organic compound film 103Rf. The organic compound film 103Bf can have a structure similar to that of the organic compound film 103Rf.
Subsequently, a sacrificial film 158Bf and a mask film 159Bf are formed in this order as illustrated in
The resist mask 190B is provided at a position overlapping with the conductive layer 152B.
Subsequently, as illustrated in
Accordingly, the stacked-layer structure of the organic compound layer 103B, the sacrificial layer 158B, and the mask layer 159B remains over the conductive layer 152B as illustrated in
Note that the side surfaces of the organic compound layers 103R, 103G, and 103B are preferably perpendicular or substantially perpendicular to their formation surfaces. For example, the angle between the formation surfaces and these side surfaces is preferably greater than or equal to 600 and less than or equal to 90°.
The distance between two adjacent layers among the organic compound layers 103R, 103G, and 103B, which are formed by a photolithography technique as described above, can be reduced to less than or equal to 8 μm, less than or equal to 5 μm, less than or equal to 3 μm, less than or equal to 2 μm, or less than or equal to 1 μm. Here, the distance can be specified, for example, by the distance between opposite end portions of two adjacent layers among the organic compound layers 103R, 103G, and 103B. Reducing the distance between the island-shaped organic compound layers makes it possible to provide a display apparatus having high resolution and a high aperture ratio. In addition, the distance between the first electrodes of adjacent organic EL devices can also be shortened to be, for example, less than or equal to 10 μm, less than or equal to 8 μm, less than or equal to 5 μm, less than or equal to 3 μm, or less than or equal to 2 μm. Note that the distance between the first electrodes of adjacent organic EL devices is preferably greater than or equal to 2 μm and less than or equal to 5 μm.
Next, the mask layers 159R, 159G, and 159B are preferably removed as illustrated in
The step of removing the mask layers can be performed by a method similar to that for the step of processing the mask film. Specifically, by using a wet etching method, damage caused to the organic compound layer 103 at the time of removing the mask layers can be reduced as compared to the case of using a dry etching method.
The mask layers may be removed by being dissolved in a polar solvent such as water or an alcohol. Examples of an alcohol include ethyl alcohol, methyl alcohol, isopropyl alcohol (IPA), and glycerin.
After the mask layers are removed, drying treatment may be performed in order to remove water adsorbed on surfaces. For example, heat treatment in an inert gas atmosphere or a reduced-pressure atmosphere can be performed. The heat treatment can be performed at a substrate temperature higher than or equal to 50° C. and lower than or equal to 200° C., preferably higher than or equal to 60° C. and lower than or equal to 150° C., and further preferably higher than or equal to 70° C. and lower than or equal to 120° C. The heat treatment is preferably performed in a reduced-pressure atmosphere, in which case drying at a lower temperature is possible.
Next, an inorganic insulating film 125f is formed as illustrated in
Then, as illustrated in
The substrate temperature at the time of forming the inorganic insulating film 125f and the insulating film 127f is preferably higher than or equal to 60° C., higher than or equal to 80° C., higher than or equal to 100° C., or higher than or equal to 120° C. and lower than or equal to 200° C., lower than or equal to 180° C., lower than or equal to 160° C., lower than or equal to 150° C., or lower than or equal to 140° C.
As the inorganic insulating film 125f, an insulating film having a thickness of 3 nm or more, 5 nm or more, or 10 nm or more and 200 nm or less, 150 nm or less, 100 nm or less, or 50 nm or less is preferably formed at a substrate temperature in the above-described range.
The inorganic insulating film 125f is preferably formed by an ALD method, for example. An ALD method is preferably used, in which case deposition damage is reduced and a film with good coverage can be formed. As the inorganic insulating film 125f, an aluminum oxide film is preferably formed by an ALD method, for example.
The insulating film 127f is preferably formed by the aforementioned wet process. For example, the insulating film 127f is preferably formed by spin coating using a photosensitive material, and specifically preferably formed using a photosensitive resin composition containing an acrylic resin.
Then, part of the insulating film 127f is exposed to visible light or ultraviolet rays. The insulating layer 127 is formed in regions that are sandwiched between any two of the conductive layers 152R, 152G, and 152B and around the conductive layer 152C.
The width of the insulating layer 127 formed later can be controlled in accordance with the exposed region of the insulating film 127f. In this embodiment, processing is performed such that the insulating layer 127 includes a portion overlapping with the top surface of the conductive layer 151.
Light used for the exposure preferably includes the i-line (wavelength: 365 nm). Furthermore, light used for the exposure may include at least one of the g-line (wavelength: 436 nm) and the h-line (wavelength: 405 nm).
Next, the region of the insulating film 127f exposed to light is removed by development as illustrated in
Next, as illustrated in
The first etching treatment can be performed by dry etching or wet etching. Note that the inorganic insulating film 125f is preferably formed using a material similar to that of the sacrificial layers 158R, 158G, and 158B, in which case the first etching treatment can be performed concurrently.
In the case of performing dry etching, a chlorine-based gas is preferably used. As the chlorine-based gas, one of Cl, BCl3, SiCl4, CCl4, and the like or a mixture of two or more of them can be used. Moreover, one of an oxygen gas, a hydrogen gas, a helium gas, an argon gas, and the like or a mixture of two or more of them can be added as appropriate to the chlorine-based gas. By the dry etching, the thin regions of the sacrificial layers 158R, 158G, and 158B can be formed with favorable in-plane uniformity.
As a dry etching apparatus, a dry etching apparatus including a high-density plasma source can be used. As the dry etching apparatus including a high-density plasma source, an inductively coupled plasma (ICP) etching apparatus can be used, for example. Alternatively, a capacitively coupled plasma (CCP) etching apparatus including parallel plate electrodes can be used.
The first etching treatment is preferably performed by wet etching. The use of a wet etching method can reduce damage to the organic compound layers 103R, 103G, and 103B, as compared to the case of using a dry etching method. Wet etching can be performed using an alkaline solution, for example. For instance, TMAH, which is an alkaline solution, can be used for the wet etching of an aluminum oxide film. Alternatively, an acid solution containing fluoride can also be used. In this case, puddle wet etching can be performed. Note that the inorganic insulating film 125f is preferably formed using a material similar to that of the sacrificial layers 158R, 158G, and 158B, in which case the above etching treatment can be performed concurrently.
The sacrificial layers 158R, 158G, and 158B are not completely removed by the first etching treatment, and the etching treatment is stopped when the thickness of the sacrificial layers 158R, 158G, and 158B is reduced. The corresponding sacrificial layers 158R, 158G, and 158B remain over the organic compound layers 103R, 103G, and 103B in this manner, whereby the organic compound layers 103R, 103G, and 103B can be prevented from being damaged by treatment in a later step.
Next, light exposure is preferably performed on the entire substrate so that the insulating layer 127a is irradiated with visible light or ultraviolet rays. The energy density for the light exposure is preferably greater than 0 mJ/cm2 and less than or equal to 800 mJ/cm2, further preferably greater than 0 mJ/cm2 and less than or equal to 500 mJ/cm2. Performing such light exposure after the development can sometimes increase the degree of transparency of the insulating layer 127a. In addition, it is sometimes possible to lower the substrate temperature required for subsequent heat treatment for changing the shape of the insulating layer 127a into a tapered shape.
Here, when a barrier insulating layer against oxygen (e.g., an aluminum oxide film) exists as each of the sacrificial layers 158R, 158G, and 158B, diffusion of oxygen into the organic compound layers 103R, 103G, and 103B can be suppressed.
Then, heat treatment (also referred to as post-baking) is performed. The heat treatment can change the insulating layer 127a into the insulating layer 127 having a tapered side surface (
When the sacrificial layers 158R, 158G, and 158B are not completely removed by the first etching treatment and the thinned sacrificial layers 158R, 158G, and 158B are left, the organic compound layers 103R, 103G, and 103B can be prevented from being damaged and deteriorating in the heat treatment. This increases the reliability of the organic EL device.
Next, as illustrated in
An end portion of the inorganic insulating layer 125 is covered with the insulating layer 127.
The second etching treatment is performed by wet etching. The use of a wet etching method can reduce damage to the organic compound layers 103R, 103G, and 103B, as compared to the case of using a dry etching method. Wet etching can be performed using an alkaline solution or an acidic solution, for example. An aqueous solution is preferably used in order that the organic compound layer 103 is not dissolved.
Next, as illustrated in
Next, as illustrated in
Then, the substrate 120 is bonded to the protective layer 131 using the resin layer 122, so that the display apparatus can be manufactured. In the method for manufacturing the display apparatus of one embodiment of the present invention, the insulating layer 156 is formed to include a region overlapping with the side surface of the conductive layer 151 and the conductive layer 152 is formed to cover the conductive layer 151 and the insulating layer 156 as described above. This can increase the yield of the display apparatus and inhibit generation of defects.
As described above, in the method for manufacturing the display apparatus in one embodiment of the present invention, the island-shaped organic compound layers 103R, 103G, and 103B are formed not by using a fine metal mask but by processing a film formed on the entire surface; thus, the island-shaped layers can be formed to have a uniform thickness. Consequently, a high-resolution display apparatus or a display apparatus with a high aperture ratio can be obtained. Furthermore, even when the resolution or the aperture ratio is high and the distance between the subpixels is extremely short, the organic compound layers 103R, 103G, and 103B can be inhibited from being in contact with each other in the adjacent subpixels. As a result, generation of leakage current between the subpixels can be inhibited. This can prevent crosstalk, so that a display apparatus with extremely high contrast can be obtained.
Moreover, even a display apparatus that includes tandem organic EL devices formed by a photolithography technique can have high moisture resistance, high water resistance, high oxygen resistance, high chemical resistance, a low driving voltage, and high emission efficiency.
In this embodiment, a display apparatus of one embodiment of the present invention will be described.
The display apparatus in this embodiment can be a high-resolution display apparatus. Thus, the display apparatus in this embodiment can be used for display portions of information terminals (wearable devices) such as watch-type and bracelet-type information terminals and display portions of wearable devices capable of being worn on a head, such as a VR device like a head mounted display (HMD) and a glasses-type AR device.
The display apparatus in this embodiment can be a high-definition display apparatus or a large-sized display apparatus. Accordingly, the display apparatus in this embodiment can be used for display portions of a digital camera, a digital video camera, a digital photo frame, a mobile phone, a portable game console, a portable information terminal, and an audio reproducing device, in addition to display portions of electronic devices with a relatively large screen, such as a television device, desktop and notebook personal computers, a monitor of a computer and the like, digital signage, and a large game machine such as a pachinko machine.
The display module 280 includes a substrate 291 and a substrate 292. The display module 280 includes a display portion 281. The display portion 281 is a region of the display module 280 where an image is displayed, and is a region where light emitted from pixels provided in a pixel portion 284 described later can be seen.
The pixel portion 284 includes a plurality of pixels 284a arranged periodically. An enlarged view of one pixel 284a is illustrated on the right side in
The pixel circuit portion 283 includes a plurality of pixel circuits 283a arranged periodically.
One pixel circuit 283a is a circuit that controls driving of a plurality of elements included in one pixel 284a.
The circuit portion 282 includes a circuit for driving the pixel circuits 283a in the pixel circuit portion 283. For example, the circuit portion 282 preferably includes one or both of a gate line driver circuit and a source line driver circuit. The circuit portion 282 may also include at least one of an arithmetic circuit, a memory circuit, a power supply circuit, and the like.
The FPC 290 functions as a wiring for supplying a video signal, a power supply potential, or the like to the circuit portion 282 from the outside. An IC may be mounted on the FPC 290.
The display module 280 can have a structure in which one or both of the pixel circuit portion 283 and the circuit portion 282 are stacked below the pixel portion 284; hence, the aperture ratio (effective display area ratio) of the display portion 281 can be significantly high.
Such a display module 280 has extremely high resolution, and thus can be suitably used for a VR device such as an HMD or a glasses-type AR device. For example, even in the case of a structure in which the display portion of the display module 280 is seen through a lens, pixels of the extremely-high-resolution display portion 281 included in the display module 280 are prevented from being recognized when the display portion is enlarged by the lens, so that display providing a high sense of immersion can be performed. Without being limited thereto, the display module 280 can be suitably used for electronic devices including a relatively small display portion.
The display apparatus 100A illustrated in
The substrate 301 corresponds to the substrate 291 in
An element isolation layer 315 is provided between two adjacent transistors 310 to be embedded in the substrate 301.
An insulating layer 261 is provided to cover the transistor 310, and the capacitor 240 is provided over the insulating layer 261.
The capacitor 240 includes a conductive layer 241, a conductive layer 245, and an insulating layer 243 between the conductive layers 241 and 245. The conductive layer 241 functions as one electrode of the capacitor 240, the conductive layer 245 functions as the other electrode of the capacitor 240, and the insulating layer 243 functions as a dielectric of the capacitor 240.
The conductive layer 241 is provided over the insulating layer 261 and is embedded in an insulating layer 254. The conductive layer 241 is electrically connected to one of the source and the drain of the transistor 310 through a plug 271 embedded in the insulating layer 261. The insulating layer 243 is provided to cover the conductive layer 241. The conductive layer 245 is provided in a region overlapping with the conductive layer 241 with the insulating layer 243 therebetween.
An insulating layer 255 is provided to cover the capacitor 240. The insulating layer 174 is provided over the insulating layer 255. The insulating layer 175 is provided over the insulating layer 174. The organic EL devices 130R, 130G, and 130B are provided over the insulating layer 175. An insulator is provided in regions between adjacent organic EL devices.
The insulating layer 156R is provided to include a region overlapping with the side surface of the conductive layer 151R. The insulating layer 156G is provided to include a region overlapping with the side surface of the conductive layer 151G. The insulating layer 156B is provided to include a region overlapping with the side surface of the conductive layer 151B. The conductive layer 152R is provided to cover the conductive layer 151R and the insulating layer 156R. The conductive layer 152G is provided to cover the conductive layer 151G and the insulating layer 156G. The conductive layer 152B is provided to cover the conductive layer 151B and the insulating layer 156B. The sacrificial layer 158R is positioned over the organic compound layer 103R. The sacrificial layer 158G is positioned over the organic compound layer 103G. The sacrificial layer 158B is positioned over the organic compound layer 103B.
Each of the conductive layers 151R, 151G, and 151B is electrically connected to one of the source and the drain of the corresponding transistor 310 through a plug 256 embedded in the insulating layers 243, 255, 174, and 175, the conductive layer 241 embedded in the insulating layer 254, and the plug 271 embedded in the insulating layer 261. Any of a variety of conductive materials can be used for the plugs.
The protective layer 131 is provided over the organic EL devices 130R, 130G, and 130B. The substrate 120 is bonded to the protective layer 131 with the resin layer 122. Embodiment 3 can be referred to for the details of the organic EL device 130 and the components thereover up to the substrate 120. The substrate 120 corresponds to the substrate 292 in
In the display apparatus 100B, a substrate 352 and a substrate 351 are bonded to each other. In
The display apparatus 100B includes the pixel portion 177, the connection portion 140, a circuit 356, a wiring 355, and the like.
The connection portion 140 is provided outside the pixel portion 177. The number of connection portions 140 may be one or more. In the connection portion 140, a common electrode of an organic EL device is electrically connected to a conductive layer, so that a potential can be supplied to the common electrode.
As the circuit 356, a scan line driver circuit can be used, for example.
The wiring 355 has a function of supplying a signal and power to the pixel portion 177 and the circuit 356. The signal and power are input to the wiring 355 from the outside through the FPC 353 or from the IC 354.
The display apparatus 100C illustrated in
Embodiments 1 to 3 can be referred to for the details of the organic EL devices 130R, 130G, and 130B.
The organic EL device 130R includes a conductive layer 224R, the conductive layer 151R over the conductive layer 224R, and the conductive layer 152R over the conductive layer 151R. The organic EL device 130G includes a conductive layer 224G, the conductive layer 151G over the conductive layer 224G, and the conductive layer 152G over the conductive layer 151G. The organic EL device 130B includes a conductive layer 224B, the conductive layer 151B over the conductive layer 224B, and the conductive layer 152B over the conductive layer 151B.
The conductive layer 224R is connected to a conductive layer 222b included in the transistor 205 through an opening provided in an insulating layer 214. An end portion of the conductive layer 151R is positioned outward from an end portion of the conductive layer 224R. The insulating layer 156R is provided to include a region that is in contact with the side surface of the conductive layer 151R, and the conductive layer 152R is provided to cover the conductive layer 151R and the insulating layer 156R.
The conductive layers 224G, 151G, and 152G and the insulating layer 156G in the organic EL device 130G are not described in detail because they are respectively similar to the conductive layers 224R, 151R, and 152R and the insulating layer 156R in the organic EL device 130R; the same applies to the conductive layers 224B, 151B, and 152B and the insulating layer 156B in the organic EL device 130B.
The conductive layers 224R, 224G, and 224B each have a depression portion covering the opening provided in the insulating layer 214. A layer 128 is embedded in the depression portion.
The layer 128 has a function of filling the depression portions of the conductive layers 224R, 224G, and 224B to obtain planarity. Over the conductive layers 224R, 224G, and 224B and the layer 128, the conductive layers 151R, 151G, and 151B that are respectively electrically connected to the conductive layers 224R, 224G, and 224B are provided. Thus, the regions overlapping with the depression portions of the conductive layers 224R, 224G, and 224B can also be used as light-emitting regions, whereby the aperture ratio of the pixel can be increased.
The layer 128 may be an insulating layer or a conductive layer. Any of a variety of inorganic insulating materials, organic insulating materials, and conductive materials can be used for the layer 128 as appropriate. Specifically, the layer 128 is preferably formed using an insulating material and is particularly preferably formed using an organic insulating material. The layer 128 can be formed using an organic insulating material usable for the insulating layer 127, for example.
The protective layer 131 is provided over the organic EL devices 130R, 130G, and 130B. The protective layer 131 and the substrate 352 are bonded to each other with an adhesive layer 142. The substrate 352 is provided with a light-block layer 157. A solid sealing structure, a hollow sealing structure, or the like can be employed to seal the organic EL device 130. In
The display apparatus 100B has a top-emission structure. Light from the organic EL device is emitted toward the substrate 352. For the substrate 352, a material having a high visible-light-transmitting property is preferably used. In the case where the organic EL device emits infrared or near-infrared light, a material having a high transmitting property with respect to infrared or near-infrared light is preferably used. The pixel electrode contains a material that reflects visible light, and the counter electrode (the common electrode 155) contains a material that transmits visible light.
An insulating layer 211, an insulating layer 213, an insulating layer 215, and the insulating layer 214 are provided in this order over the substrate 351. Part of the insulating layer 211 functions as a gate insulating layer of each transistor. Part of the insulating layer 213 functions as a gate insulating layer of each transistor. The insulating layer 215 is provided to cover the transistors. The insulating layer 214 is provided to cover the transistors and has a function of a planarization layer. Note that the number of gate insulating layers and the number of insulating layers covering the transistors are not limited and may each be one or more.
An inorganic insulating film is preferably used as each of the insulating layers 211, 213, and 215.
An organic insulating layer is suitable for the insulating layer 214 functioning as a planarization layer.
Each of the transistors 201 and 205 includes a conductive layer 221 functioning as a gate, the insulating layer 211 functioning as the gate insulating layer, a conductive layer 222a and the conductive layer 222b functioning as a source and a drain, a semiconductor layer 231, the insulating layer 213 functioning as the gate insulating layer, and a conductive layer 223 functioning as a gate.
A connection portion 204 is provided in a region of the substrate 351 not overlapping with the substrate 352. In the connection portion 204, the source electrode or the drain electrode of the transistor 201 is electrically connected to the FPC 353 through a conductive layer 166 and a connection layer 242. As an example, the conductive layer 166 has a stacked-layer structure of a conductive film obtained by processing the same conductive film as the conductive layers 224R, 224G, and 224B; a conductive film obtained by processing the same conductive film as the conductive layers 151R, 151G, and 151B; and a conductive film obtained by processing the same conductive film as the conductive layers 152R, 152G, and 152B. On the top surface of the connection portion 204, the conductive layer 166 is exposed. Thus, the connection portion 204 and the FPC 353 can be electrically connected to each other through the connection layer 242.
The light-block layer 157 is preferably provided on the surface of the substrate 352 on the substrate 351 side. The light-block layer 157 can be provided over a region between adjacent organic EL devices, in the connection portion 140, in the circuit 356, and the like. A variety of optical members can be arranged on the outer surface of the substrate 352.
A material that can be used for the substrate 120 can be used for each of the substrates 351 and 352.
A material that can be used for the resin layer 122 can be used for the adhesive layer 142.
As the connection layer 242, an anisotropic conductive film (ACF), an anisotropic conductive paste (ACP), or the like can be used.
The display apparatus 100D illustrated in
Light from the organic EL device is emitted toward the substrate 351. For the substrate 351, a material having a high visible-light-transmitting property is preferably used. By contrast, there is no limitation on the light-transmitting property of a material used for the substrate 352.
The light-block layer is preferably formed between the substrate 351 and the transistor 201 and between the substrate 351 and the transistor 205.
The organic EL device 130R includes a conductive layer 112R, a conductive layer 126R over the conductive layer 112R, and a conductive layer 129R over the conductive layer 126R.
The organic EL device 130B includes a conductive layer 112B, a conductive layer 126B over the conductive layer 112B, and a conductive layer 129B over the conductive layer 126B.
A material having a high visible-light-transmitting property is used for each of the conductive layers 112R, 112B, 126R, 126B, 129R, and 129B. A material that reflects visible light is preferably used for the common electrode 155.
Although not illustrated in
Although
The display apparatus 100E illustrated in
In the display apparatus 100E, the organic EL device 130 includes a region overlapping with one of the coloring layers 132R, 132G, and 132B. The coloring layers 132R, 132G, and 132B can be provided on a surface of the substrate 352 on the substrate 351 side. End portions of the coloring layers 132R, 132G, and 132B can overlap with the light-block layer 157.
In the display apparatus 100E, the organic EL device 130 can emit white light, for example. The coloring layer 132R, the coloring layer 132G, and the coloring layer 132B can transmit red light, green light, and blue light, respectively, for example. Note that in the display apparatus 100E, the coloring layers 132R, 132G, and 132B may be provided between the protective layer 131 and the adhesive layer 142.
Although
This embodiment can be combined as appropriate with the other embodiments or the examples. In this specification, in the case where a plurality of structure examples are shown in one embodiment, the structure examples can be combined as appropriate.
In this embodiment, electronic devices of one embodiment of the present invention will be described.
Electronic devices of this embodiment include the display apparatus of one embodiment of the present invention in their display portions. The display apparatus of one embodiment of the present invention has high display performance and can be easily increased in resolution and definition. Thus, the display apparatus of one embodiment of the present invention can be used for display portions of a variety of electronic devices.
Examples of the electronic devices include a digital camera, a digital video camera, a digital photo frame, a mobile phone, a portable game console, a portable information terminal, and an audio reproducing device, in addition to electronic devices with a relatively large screen, such as a television device, desktop and notebook personal computers, a monitor of a computer and the like, digital signage, and a large game machine such as a pachinko machine.
In particular, the display apparatus of one embodiment of the present invention can have high resolution, and thus can be favorably used for an electronic device having a relatively small display portion. Examples of such an electronic device include watch-type and bracelet-type information terminal devices (wearable devices) and wearable devices worn on the head, such as a VR device like a head-mounted display, a glasses-type AR device, and an MR device.
The electronic device in this embodiment may include a sensor (a sensor having a function of measuring force, displacement, position, speed, acceleration, angular velocity, rotational frequency, distance, light, liquid, magnetism, temperature, a chemical substance, sound, time, hardness, electric field, current, voltage, electric power, radiation, flow rate, humidity, gradient, oscillation, odor, or infrared rays).
Examples of head-mounted wearable devices are described with reference to
An electronic device 700A illustrated in
The display apparatus of one embodiment of the present invention can be used for the display panels 751. Thus, the electronic devices can be highly reliable.
The electronic devices 700A and 700B can each project images displayed on the display panels 751 onto display regions 756 of the optical members 753. Since the optical members 753 have a light-transmitting property, the user can see images displayed on the display regions, which are superimposed on transmission images seen through the optical members 753.
In the electronic devices 700A and 700B, a camera capable of capturing images of the front side may be provided as the image capturing portion. Furthermore, when the electronic devices 700A and 700B are provided with an acceleration sensor such as a gyroscope sensor, the orientation of the user's head can be sensed and an image corresponding to the orientation can be displayed on the display regions 756.
The communication portion includes a wireless communication device, and a video signal, for example, can be supplied by the wireless communication device. Instead of or in addition to the wireless communication device, a connector that can be connected to a cable for supplying a video signal and a power supply potential may be provided.
The electronic devices 700A and 700B are provided with a battery, so that they can be charged wirelessly and/or by wire.
A touch sensor module may be provided in the housing 721.
Various touch sensors can be applied to the touch sensor module. For example, any of touch sensors of the following types can be used: a capacitive type, a resistive type, an infrared type, an electromagnetic induction type, a surface acoustic wave type, and an optical type. In particular, a capacitive sensor or an optical sensor is preferably used for the touch sensor module.
An electronic device 800A illustrated in
The display apparatus of one embodiment of the present invention can be used in the display portions 820. Thus, the electronic devices can be highly reliable.
The display portions 820 are positioned inside the housing 821 so as to be seen through the lenses 832. When the pair of display portions 820 display different images, three-dimensional display using parallax can be performed.
The electronic devices 800A and 800B preferably include a mechanism for adjusting the lateral positions of the lenses 832 and the display portions 820 so that the lenses 832 and the display portions 820 are positioned optimally in accordance with the positions of the user's eyes.
The electronic device 800A or the electronic device 800B can be mounted on the user's head with the wearing portions 823.
The image capturing portion 825 has a function of obtaining information on the external environment. Data obtained by the image capturing portion 825 can be output to the display portion 820. An image sensor can be used for the image capturing portion 825. Moreover, a plurality of cameras may be provided so as to cover a plurality of fields of view, such as a telescope field of view and a wide field of view.
The electronic device 800A may include a vibration mechanism that functions as bone-conduction earphones.
The electronic devices 800A and 800B may each include an input terminal. To the input terminal, a cable for supplying a video signal from a video output device or the like, power for charging a battery provided in the electronic device, and the like can be connected.
The electronic device of one embodiment of the present invention may have a function of performing wireless communication with earphones 750.
The electronic device may include an earphone portion. The electronic device 700B in
Similarly, the electronic device 800B in
As described above, both the glasses-type device (e.g., the electronic devices 700A and 700B) and the goggles-type device (e.g., the electronic devices 800A and 800B) are preferable as the electronic device of one embodiment of the present invention.
An electronic device 6500 illustrated in
The electronic device 6500 includes a housing 6501, a display portion 6502, a power button 6503, buttons 6504, a speaker 6505, a microphone 6506, a camera 6507, a light source 6508, and the like. The display portion 6502 has a touch panel function.
The display apparatus of one embodiment of the present invention can be used in the display portion 6502. Thus, the electronic device can be highly reliable.
A protection member 6510 having a light-transmitting property is provided on the display surface side of the housing 6501. A display panel 6511, an optical member 6512, a touch sensor panel 6513, a printed circuit board 6517, a battery 6518, and the like are provided in a space surrounded by the housing 6501 and the protection member 6510.
The display panel 6511, the optical member 6512, and the touch sensor panel 6513 are fixed to the protection member 6510 with an adhesive layer (not illustrated).
Part of the display panel 6511 is folded back in a region outside the display portion 6502, and an FPC 6515 is connected to the part that is folded back. An IC 6516 is mounted on the FPC 6515. The FPC 6515 is connected to a terminal provided on the printed circuit board 6517.
The display apparatus of one embodiment of the present invention can be used in the display panel 6511. Thus, the electronic device can be extremely lightweight. Since the display panel 6511 is extremely thin, the battery 6518 with high capacity can be mounted without an increase in the thickness of the electronic device. Moreover, part of the display panel 6511 is folded back so that a connection portion with the FPC 6515 is provided on the back side of the pixel portion, whereby the electronic device can have a narrow bezel.
The display apparatus of one embodiment of the present invention can be used in the display portion 7000. Thus, a highly reliable electronic device is obtained.
Operation of the television device 7100 illustrated in
The display apparatus of one embodiment of the present invention can be used in the display portion 7000. Thus, a highly reliable electronic device is obtained.
Digital signage 7300 illustrated in
In
A larger area of the display portion 7000 can increase the amount of information that can be provided at a time. The display portion 7000 having a larger area attracts more attention, so that the effectiveness of the advertisement can be increased, for example.
As illustrated in
Electronic devices illustrated in
The electronic devices illustrated in
The electronic devices in
This embodiment can be combined as appropriate with the other embodiments or the examples. In this specification, in the case where a plurality of structure examples are shown in one embodiment, the structure examples can be combined as appropriate.
Described in this example are specific methods for fabricating a light-emitting device 1 of one embodiment of the present invention, a comparative light-emitting device 1-1, and a comparative light-emitting device 1-2, and characteristics of the light-emitting devices. Structural formulae of main compounds used in this example are shown below.
First, 100-nm-thick silver (Ag) and 85-nm-thick indium tin oxide containing silicon oxide (ITSO) were stacked over a glass substrate sequentially from the substrate side by a sputtering method as a reflective electrode and a transparent electrode, respectively, whereby the first electrode 101 with a size of 2 mm×2 mm was formed. Note that the transparent electrode functions as an anode, and the transparent electrode and the reflective electrode are collectively regarded as the first electrode 101.
Next, in pretreatment for forming the light-emitting device over a substrate, the surface of the substrate was washed with water, and baking was performed at 200° C. for one hour.
After that, the substrate was transferred into a vacuum evaporation apparatus where the pressure was reduced to approximately 1×10−4 Pa, and was subjected to vacuum baking at 170° C. for 30 minutes in a heating chamber of the vacuum evaporation apparatus, and then the substrate was cooled down for approximately 30 minutes.
Then, the substrate provided with the first electrode 101 was fixed to a holder provided in the vacuum evaporation apparatus such that the surface on which the first electrode 101 was formed faced downward. Over the first electrode 101, N-(biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H-fluoren-2-amine (abbreviation: PCBBiF) represented by Structural Formula (i) above and an electron-accepting material having 4 or more fluorine atoms and a molecular weight of 672 (OCHD-003) were deposited by co-evaporation to a thickness of 10 nm such that the weight ratio of PCBBiF to OCHD-003 was 1:0.03, whereby the hole-injection layer 111 was formed.
Over the hole-injection layer 111, PCBBiF was deposited by evaporation to a thickness of 90 nm, whereby a first hole-transport layer was formed.
Then, over the first hole-transport layer, 8-(1,1′:4′,1″-terphenyl-3-yl)-4-[3-(dibenzothiophen-4-yl)phenyl]-[1]benzofuro[3,2-d]pyrimidine (abbreviation: 8mpTP-4mDBtPBfpm) represented by Structural Formula (ii) above, 9-(2-naphthyl)-9′-phenyl-9H,9′H-3,3′-bicarbazole (abbreviation: PNCCP) represented by Structural Formula (iii) above, and [2-d3-methyl-8-(2-pyridinyl-κN)benzofuro[2,3-b]pyridine-KC]bis[2-(5-d3-methyl-2-pyridinyl-κN2)phenyl-κC]iridium(III) (abbreviation: Ir(5mppy-d3)2(mbfpypy-d3)) represented by Structural Formula (iv) above were deposited by co-evaporation to a thickness of 40 nm such that the weight ratio of 8mpTP-4mDBtPBfpm to PNCCP and Ir(5mppy-d3)2(mbfpypy-d3) was 0.5:0.5:0.1, whereby a first light-emitting layer was formed.
Next, 2-{3-[3-(N-phenyl-9H-carbazol-3-yl)-9H-carbazol-9-yl]phenyl}dibenzo[f,h]quinoxaline (abbreviation: 2mPCCzPDBq) represented by Structural Formula (v) above was deposited by evaporation to a thickness of 10 nm to form a first electron-transport layer.
After the first electron-transport layer was formed, 2,9-di(naphthalen-2-yl)-4,7-diphenyl-1,10-phenanthroline (abbreviation: NBPhen) represented by Structural Formula (vi) above and 4,7-di-1-pyrrolidinyl-1,10-phenanthroline (abbreviation: Pyrrd-Phen) represented by Structural Formula (vii) above were deposited by co-evaporation to a thickness of 5 nm such that the weight ratio of NBPhen to Pyrrd-Phen was 0.5:0.5, and then indium oxide (In2O3) was deposited by evaporation to a thickness of 2 nm to form a first region. Then, copper phthalocyanine (abbreviation: CuPc) represented by Structural Formula (viii) above was deposited by evaporation to a thickness of 2 nm to form a third region. Furthermore, PCBBiF and OCHD-003 were deposited by co-evaporation to a thickness of 10 nm such that the weight ratio of PCBBiF to OCHD-003 was 1:0.15 to form a second region. Thus, an intermediate layer was formed.
Over the intermediate layer, PCBBiF was deposited by evaporation to a thickness of 55 nm, whereby a second hole-transport layer was formed.
Over the second hole-transport layer, 8mpTP-4mDBtPBfpm, PNCCP, and Ir(5mppy-d3)2(mbfpypy-d3) were deposited by co-evaporation to a thickness of 40 nm such that the weight ratio of 8mpTP-4mDBtPBfpm to PNCCP and Ir(5mppy-d3)2(mbfpypy-d3) was 0.5:0.5:0.1, whereby a second light-emitting layer was formed.
Then, 2mPCCzPDBq was deposited by evaporation to a thickness of 20 nm, and 2,2′-(1,3-phenylene)bis(9-phenyl-1,10-phenanthroline) (abbreviation: mPPhen2P) represented by Structural Formula (ix) above was further deposited by evaporation to a thickness of 20 nm, whereby a second electron-transport layer was formed.
A sample in which the second electron-transport layer and the components thereunder had been formed was exposed to an air atmosphere for one hour. After that, the sample was subjected to vacuum baking at 110° C. for 60 minutes in a heating chamber of the vacuum evaporation apparatus where the pressure was reduced to approximately 1×10−4 Pa.
After that, lithium fluoride (LiF) and ytterbium (Yb) were deposited by co-evaporation to a thickness of 1.5 nm such that the volume ratio of LiF to Yb was 1:0.5, and then silver (Ag) and magnesium (Mg) were deposited by co-evaporation to a thickness of 15 nm such that the volume ratio of Ag to Mg was 1:0.1, whereby the second electrode 102 was formed. Over the second electrode 102, 4,4′,4″-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation: DBT3P-II) represented by Structural Formula (x) above was deposited to a thickness of 70 nm as a cap layer to improve light extraction efficiency.
Then, the light-emitting device was sealed using a glass substrate in a glove box containing a nitrogen atmosphere so as not to be exposed to the air. Specifically, a UV curable sealing material was applied to surround the device, only the sealing material was irradiated with UV while the light-emitting device was not irradiated with the UV, and heat treatment was performed at 80° C. under an atmospheric pressure for one hour. In this manner, the light-emitting device 1 was fabricated.
The comparative light-emitting device 1-1 was fabricated in a manner similar to that of the light-emitting device 1 except that after the first electron-transport layer was formed in the fabrication process of the light-emitting device 1, NBPhen and Pyrrd-Phen were deposited by co-evaporation to a thickness of 5 nm such that the weight ratio of NBPhen to Pyrrd-Phen was 0.5:0.5, and then indium (In) was deposited by evaporation to a thickness of 2 nm to form the first region, and the second electrode 102 was formed successively after the formation of the second electron-transport layer without exposure to the air.
The comparative light-emitting device 1-2 was fabricated in a manner similar to that of the light-emitting device 1 except that after the first electron-transport layer was formed in the fabrication process of the light-emitting device 1, NBPhen and Pyrrd-Phen were deposited by co-evaporation to a thickness of 5 nm such that the weight ratio of NBPhen to Pyrrd-Phen was 0.5:0.5, and the first region was formed without depositing a metal and a metal oxide by evaporation.
Device structures of the light-emitting device 1 and the comparative light-emitting devices 1-1 and 1-2 are shown below.
As can be seen from
Described in this example are specific methods for fabricating a light-emitting device 2 of one embodiment of the present invention, and a comparative light-emitting device 2-1 to a comparative light-emitting device 2-4, and characteristics of the light-emitting devices. Structural formulae of main compounds used in this example are shown below.
First, 100-nm-thick silver (Ag) and 85-nm-thick indium tin oxide containing silicon oxide (ITSO) were stacked over a glass substrate sequentially from the substrate side by a sputtering method as a reflective electrode and a transparent electrode, respectively, whereby the first electrode 101 with a size of 2 mm×2 mm was formed. Note that the transparent electrode functions as an anode, and the transparent electrode and the reflective electrode are collectively regarded as the first electrode 101.
Next, in pretreatment for forming the light-emitting device over a substrate, the surface of the substrate was washed with water, and baking was performed at 200° C. for one hour.
After that, the substrate was transferred into a vacuum evaporation apparatus where the pressure was reduced to approximately 1×10−4 Pa, and was subjected to vacuum baking at 170° C. for 30 minutes in a heating chamber of the vacuum evaporation apparatus, and then the substrate was cooled down for approximately 30 minutes.
Then, the substrate provided with the first electrode 101 was fixed to a holder provided in the vacuum evaporation apparatus such that the surface on which the first electrode 101 was formed faced downward. Over the first electrode 101, N-(biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H-fluoren-2-amine (abbreviation: PCBBiF) represented by Structural Formula (i) above and an electron-accepting material having 4 or more fluorine atoms and a molecular weight of 672 (OCHD-003) were deposited by co-evaporation to a thickness of 10 nm such that the weight ratio of PCBBiF to OCHD-003 was 1:0.03, whereby the hole-injection layer 111 was formed.
Over the hole-injection layer 111, PCBBiF was deposited by evaporation to a thickness of 90 nm, whereby a first hole-transport layer was formed.
Then, over the first hole-transport layer, 8-(1,1′:4′,1″-terphenyl-3-yl)-4-[3-(dibenzothiophen-4-yl)phenyl]-[1]benzofuro[3,2-d]pyrimidine (abbreviation: 8mpTP-4mDBtPBfpm) represented by Structural Formula (ii) above, 9-(2-naphthyl)-9′-phenyl-9H,9′H-3,3′-bicarbazole (abbreviation: PNCCP) represented by Structural Formula (iii) above, and [2-d3-methyl-8-(2-pyridinyl-κN)benzofuro[2,3-b]pyridine-C]bis[2-(5-d3-methyl-2-pyridinyl-κN2)phenyl-κC]iridium(III) (abbreviation: Ir(5mppy-d3)2(mbfpypy-d3)) represented by Structural Formula (iv) above were deposited by co-evaporation to a thickness of 40 nm such that the weight ratio of 8mpTP-4mDBtPBfpm to PNCCP and Ir(5mppy-d3)2(mbfpypy-d3) was 0.5:0.5:0.1, whereby a first light-emitting layer was formed.
Next, 2-{3-[3-(N-phenyl-9H-carbazol-3-yl)-9H-carbazol-9-yl]phenyl}dibenzo[f,h]quinoxaline (abbreviation: 2mPCCzPDBq) represented by Structural Formula (v) above was deposited by evaporation to a thickness of 10 nm to form a first electron-transport layer.
After the first electron-transport layer was formed, 2,2′-(1,3-phenylene)bis(9-phenyl-1,10-phenanthroline) (abbreviation: mPPhen2P) represented by Structural Formula (ix) above and 4,7-di-1-pyrrolidinyl-1,10-phenanthroline (abbreviation: Pyrrd-Phen) represented by Structural Formula (vii) above were deposited by co-evaporation to a thickness of 5 nm such that the weight ratio of mPPhen2P to Pyrrd-Phen was 0.5:0.5, and then lithium oxide (Li2O) was deposited by evaporation to a thickness of 0.2 nm to form a first region. Then, copper phthalocyanine (abbreviation: CuPc) represented by Structural Formula (viii) above was deposited by evaporation to a thickness of 2 nm to form a third region. Furthermore, PCBBiF and OCHD-003 were deposited by co-evaporation to a thickness of 10 nm such that the weight ratio of PCBBiF to OCHD-003 was 1:0.15 to form a second region. Thus, an intermediate layer was formed.
Over the intermediate layer, PCBBiF was deposited by evaporation to a thickness of 55 nm, whereby a second hole-transport layer was formed.
Over the second hole-transport layer, 8mpTP-4mDBtPBfpm, PNCCP, and Ir(5mppy-d3)2(mbfpypy-d3) were deposited by co-evaporation to a thickness of 40 nm such that the weight ratio of 8mpTP-4mDBtPBfpm to PNCCP and Ir(5mppy-d3)2(mbfpypy-d3) was 0.5:0.5:0.1, whereby a second light-emitting layer was formed.
Then, 2mPCCzPDBq was deposited by evaporation to a thickness of 20 nm, and mPPhen2P was further deposited by evaporation to a thickness of 20 nm, whereby a second electron-transport layer was formed.
A sample in which the second electron-transport layer and the components thereunder had been formed was exposed to an air atmosphere for one hour. After that, the sample was subjected to vacuum baking at 90° C. for one hour in a heating chamber of the vacuum evaporation apparatus where the pressure was reduced to approximately 1×10−4 Pa.
After that, lithium fluoride (LiF) and ytterbium (Yb) were deposited by co-evaporation to a thickness of 1.5 nm such that the volume ratio of LiF to Yb was 1:0.5, and then silver (Ag) and magnesium (Mg) were deposited by co-evaporation to a thickness of 15 nm such that the volume ratio of Ag to Mg was 1:0.1, whereby the second electrode 102 was formed. Over the second electrode 102, 4,4′,4″-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation: DBT3P-II) represented by Structural Formula (x) above was deposited to a thickness of 70 nm as a cap layer to improve light extraction efficiency.
Then, the light-emitting device was sealed using a glass substrate in a glove box containing a nitrogen atmosphere so as not to be exposed to the air. Specifically, a UV curable sealing material was applied to surround the device, only the sealing material was irradiated with UV while the light-emitting device was not irradiated with the UV, and heat treatment was performed at 80° C. under an atmospheric pressure for one hour. In this manner, the light-emitting device 2 was fabricated.
The comparative light-emitting device 2-1 was fabricated in a manner similar to that of the light-emitting device 2 except that Pyrrd-Phen in the light-emitting device 2 was replaced with 2mPCCzPDBq.
The comparative light-emitting device 2-2 was fabricated in a manner similar to that of the light-emitting device 2 except that Pyrrd-Phen in the light-emitting device 2 was replaced with bathophenanthroline (abbreviation: BPhen) represented by Structural Formula (xi) above.
The comparative light-emitting device 2-3 was fabricated in a manner similar to that of the light-emitting device 2 except that Pyrrd-Phen in the light-emitting device 2 was replaced with 2,9-di(naphthalen-2-yl)-4,7-diphenyl-1,10-phenanthroline (abbreviation: NBPhen) represented by Structural Formula (vi) above.
The comparative light-emitting device 2-4 was fabricated in a manner similar to that of the light-emitting device 2 except that Pyrrd-Phen in the light-emitting device 2 was replaced with 2-[3-(2,6-dimethyl-3-pyridinyl)-5-(9-phenanthrenyl)phenyl]-4,6-diphenyl-1,3,5-triazine (abbreviation: mPn-mDMePyPTzn) represented by Structural Formula (xii) above.
Device structures of the light-emitting device 2 and the comparative light-emitting devices 2-1 to 2-4 are shown below.
Described in this example are specific methods for fabricating a light-emitting device 3 of one embodiment of the present invention, and a comparative light-emitting device 3-1 to a comparative light-emitting device 3-3, and characteristics of the light-emitting devices. Structural formulae of main compounds used in this example are shown below.
First, 100-nm-thick alloy of silver, palladium, and copper (Ag—Pd—Cu, also referred to as APC) and 50-nm-thick indium tin oxide containing silicon oxide (JTSO) were stacked over a glass substrate sequentially from the substrate side by a sputtering method as a reflective electrode and a transparent electrode, respectively, whereby the first electrode 101 with a size of 2 mm×2 mm was formed. Note that the transparent electrode functions as an anode, and the transparent electrode and the reflective electrode are collectively regarded as the first electrode 101.
Next, in pretreatment for forming the light-emitting device over a substrate, the surface of the substrate was washed with water, and baking was performed at 200° C. for one hour.
After that, the substrate was transferred into a vacuum evaporation apparatus where the pressure was reduced to approximately 1×10−4 Pa, and was subjected to vacuum baking at 170° C. for 30 minutes in a heating chamber of the vacuum evaporation apparatus, and then the substrate was cooled down for approximately 30 minutes.
Then, the substrate provided with the first electrode 101 was fixed to a holder provided in the vacuum evaporation apparatus such that the surface on which the first electrode 101 was formed faced downward. Over the first electrode 101, N-(biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H-fluoren-2-amine (abbreviation: PCBBiF) represented by Structural Formula (i) above and an electron-accepting material having 4 or more fluorine atoms and a molecular weight of 672 (OCHD-003) were deposited by co-evaporation to a thickness of 10 nm such that the weight ratio of PCBBiF to OCHD-003 was 1:0.03, whereby the hole-injection layer 111 was formed.
Over the hole-injection layer 111, PCBBiF was deposited by evaporation to a thickness of 135 nm, whereby a first hole-transport layer was formed.
Then, over the first hole-transport layer, 8-(1,1′:4′,1″-terphenyl-3-yl)-4-[3-(dibenzothiophen-4-yl)phenyl]-[1]benzofuro[3,2-d]pyrimidine (abbreviation: 8mpTP-4mDBtPBfpm) represented by Structural Formula (ii) above, 9-(2-naphthyl)-9′-phenyl-9H,9′H-3,3′-bicarbazole (abbreviation: PNCCP) represented by Structural Formula (iii) above, and [2-d3-methyl-8-(2-pyridinyl-κN)benzofuro[2,3-b]pyridine-C]bis[2-(5-d3-methyl-2-pyridinyl-κN2)phenyl-κC]iridium(III) (abbreviation: Ir(5mppy-d3)2(mbfpypy-d3)) represented by Structural Formula (iv) above were deposited by co-evaporation to a thickness of 40 nm such that the weight ratio of 8mpTP-4mDBtPBfpm to PNCCP and Ir(5mppy-d3)2(mbfpypy-d3) was 0.5:0.5:0.1, whereby a first light-emitting layer was formed.
Next, 2-{3-[3-(N-phenyl-9H-carbazol-3-yl)-9H-carbazol-9-yl]phenyl}dibenzo[f,h]quinoxaline (abbreviation: 2mPCCzPDBq) represented by Structural Formula (v) above was deposited by evaporation to a thickness of 10 nm to form a first electron-transport layer.
After the first electron-transport layer was formed, 2,9-di(naphthalen-2-yl)-4,7-diphenyl-1,10-phenanthroline (abbreviation: NBPhen) represented by Structural Formula (vi) above, 4,7-di-1-pyrrolidinyl-1,10-phenanthroline (abbreviation: Pyrrd-Phen) represented by Structural Formula (vii) above, and lithium oxide (Li2O) were deposited by co-evaporation to a thickness of 5 nm such that the volume ratio of NBPhen to Pyrrd-Phen and Li2O was 0.5:0.5:0.02, so that a first region was formed. Then, copper phthalocyanine (abbreviation: CuPc) represented by Structural Formula (viii) above was deposited by evaporation to a thickness of 2 nm to form a third region. Furthermore, PCBBiF and OCHD-003 were deposited by co-evaporation to a thickness of 10 nm such that the weight ratio of PCBBiF to OCHD-003 was 1:0.15 to forma second region. Thus, an intermediate layer was formed.
Over the intermediate layer, PCBBiF was deposited by evaporation to a thickness of 55 nm, whereby a second hole-transport layer was formed.
Over the second hole-transport layer, 8mpTP-4mDBtPBfpm, PNCCP, and Ir(5mppy-d3)2(mbfpypy-d3) were deposited by co-evaporation to a thickness of 40 nm such that the weight ratio of 8mpTP-4mDBtPBfpm to PNCCP and Ir(5mppy-d3)2(mbfpypy-d3) was 0.5:0.5:0.1, whereby a second light-emitting layer was formed.
Then, 2mPCCzPDBq was deposited by evaporation to a thickness of 20 nm, and 2,2′-(1,3-phenylene)bis(9-phenyl-1,10-phenanthroline) (abbreviation: mPPhen2P) represented by Structural Formula (ix) above was further deposited by evaporation to a thickness of 20 nm, whereby a second electron-transport layer was formed.
A sample in which the second electron-transport layer and the components thereunder had been formed was taken out from the vacuum evaporation apparatus and exposed to the air. After that, aluminum oxide was deposited to a thickness of 30 nm by an ALD method using trimethylaluminum (abbreviation: TMA) as a precursor and water vapor as an oxidizer to form a first sacrificial layer.
Next, over the first sacrificial layer, molybdenum was deposited to a thickness of 50 nm by a sputtering method to form a second sacrificial layer.
A resist was formed using a photoresist over the second sacrificial layer, and processing was performed by a lithography technique to form a slit having a width of 3 μm in a position 3.5 μm away from an end portion of the first electrode.
Specifically, the second sacrificial layer was processed using an etching gas containing tetrafluoromethane (CF4), oxygen (O2), and helium (He) at a flow rate ratio of CF4:O2:He=100:67:333 and an etching gas containing oxygen (O2) with the use of the resist as a mask. Then, the first sacrificial layer was processed using a basic chemical solution containing tetramethyl ammonium hydroxide (abbreviation: TMAH) and water as a solvent and an etching gas containing fluoroform (CHF3) and helium (He) at a flow rate ratio of CHF3:He=1:49. After that, the second electron-transport layer, the second light-emitting layer, the second hole-transport layer, the intermediate layer, the first electron-transport layer, the first light-emitting layer, the first hole-transport layer, and the hole-injection layer were processed using an etching gas containing oxygen (O2).
After the processing with the photolithography technique, the second sacrificial layer was removed using an etching gas containing sulfur hexafluoride (SF6) and oxygen (O2) at a flow rate ratio of SF6:O2=10:4 and an etching gas containing oxygen (O2). Then, the first sacrificial layer was removed using a basic chemical solution containing tetramethyl ammonium hydroxide (abbreviation: TMAH) and water as a solvent, so that the top surface of the second electron-transport layer was exposed. Then, the substrate was transferred into a vacuum evaporation apparatus where the pressure was reduced to approximately 1×10−4 Pa, and heat treatment was performed at 110° C. for one hour in a heating chamber of the vacuum evaporation apparatus.
After that, lithium fluoride (LiF) and ytterbium (Yb) were deposited by co-evaporation to a thickness of 1.5 nm such that the volume ratio of LiF to Yb was 1:0.5, and then silver (Ag) and magnesium (Mg) were deposited by co-evaporation to a thickness of 15 nm such that the volume ratio of Ag to Mg was 1:0.1, whereby the second electrode 102 was formed. Over the second electrode 102, 4,4′,4″-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation: DBT3P-II) represented by Structural Formula (x) above was deposited to a thickness of 70 nm as a cap layer to improve light extraction efficiency.
Then, the light-emitting device was sealed using a glass substrate in a glove box containing a nitrogen atmosphere so as not to be exposed to the air. Specifically, a UV curable sealing material was applied to surround the device, only the sealing material was irradiated with UV while the light-emitting device was not irradiated with the UV, and heat treatment was performed at 80° C. under an atmospheric pressure for one hour. In this manner, the light-emitting device 3 was fabricated.
The comparative light-emitting device 3-1 was fabricated in a manner similar to that of the light-emitting device 3 except that the second electrode 102 was formed successively after the formation of the second electron-transport layer without processing with the photolithography technique in the fabrication process of the light-emitting device 3.
The comparative light-emitting device 3-2 was fabricated in a manner similar to that of the light-emitting device 3 except that after the first electron-transport layer was formed in the fabrication process of the light-emitting device 3, mPPhen2P and lithium oxide (Li2O) were deposited by co-evaporation to a thickness of 5 nm such that the volume ratio of mPPhen2P to Li2O was 1:0.02, so that a first region was formed.
The comparative light-emitting device 3-3 was fabricated in a manner similar to that of the comparative light-emitting device 3-2 except that the second electrode 102 was formed successively after the formation of the second electron-transport layer without processing with the photolithography technique in the fabrication process of the comparative light-emitting device 3-2.
Device structures of the light-emitting device 3 and the comparative light-emitting devices 3-1 to 3-3 are shown below.
As can be seen from
The comparative light-emitting device 3-2, which was fabricated without using Pyrrd-Phen in the first region of the intermediate layer and processed by the photolithography technique, has increased driving voltage and lowered current efficiency as compared with the comparative light-emitting device 3-3 fabricated by a continuous vacuum process. This is a result of deterioration of Li2O due to exposure to the air and water in the photolithography process and loss of donor property.
In contrast, the light-emitting device 3 of one embodiment of the present invention, which includes the metal oxide and Pyrrd-Phen as an organic compound in the first region of the intermediate layer, exhibits favorable characteristics comparable to those of the light-emitting device fabricated by a continuous vacuum process, even though the light-emitting device 3 was fabricated through processing with the photolithography technique. This is because Pyrrd-Phen has a phenanthroline skeleton with an electron-donating group to increase the electron density of the phenanthroline skeleton, and the interaction between Pyrrd-Phen and Li2O as the metal oxide becomes strong, so that the donor property is improved.
As described above, in the light-emitting device of one embodiment of the present invention, electrons are easily injected and transported from the intermediate layer to the electron-transport layer even when the light-emitting device is processed by the photolithography technique, so that a light-emitting device with a low driving voltage can be obtained.
Described in this example are specific methods for fabricating a light-emitting device 4 and a light-emitting device 5 of one embodiment of the present invention, a comparative light-emitting device 4, and a comparative light-emitting device 5, and characteristics of the light-emitting devices. Structural formulae of main compounds used in this example are shown below.
First, 100-nm-thick alloy of silver, palladium, and copper (Ag—Pd—Cu, also referred to as APC) and 50-nm-thick indium tin oxide containing silicon oxide (JTSO) were stacked over a glass substrate sequentially from the substrate side by a sputtering method as a reflective electrode and a transparent electrode, respectively, whereby the first electrode 101 with a size of 2 mm×2 mm was formed. Note that the transparent electrode functions as an anode, and the transparent electrode and the reflective electrode are collectively regarded as the first electrode 101.
Next, in pretreatment for forming the light-emitting device over a substrate, the surface of the substrate was washed with water, and baking was performed at 200° C. for one hour.
After that, the substrate was transferred into a vacuum evaporation apparatus where the pressure was reduced to approximately 1×10−4 Pa, and was subjected to vacuum baking at 170° C. for 30 minutes in a heating chamber of the vacuum evaporation apparatus, and then the substrate was cooled down for approximately 30 minutes.
Then, the substrate provided with the first electrode 101 was fixed to a holder provided in the vacuum evaporation apparatus such that the surface on which the first electrode 101 was formed faced downward. Over the first electrode 101, N-(biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H-fluoren-2-amine (abbreviation: PCBBiF) represented by Structural Formula (i) above and an electron-accepting material having 4 or more fluorine atoms and a molecular weight of 672 (OCHD-003) were deposited by co-evaporation to a thickness of 10 nm such that the weight ratio of PCBBiF to OCHD-003 was 1:0.03, whereby the hole-injection layer 111 was formed.
Over the hole-injection layer 111, PCBBiF was deposited by evaporation to a thickness of 125 nm, whereby a first hole-transport layer was formed.
Then, over the first hole-transport layer, 8-(1,1′:4′,1″-terphenyl-3-yl)-4-[3-(dibenzothiophen-4-yl)phenyl]-[1]benzofuro[3,2-d]pyrimidine (abbreviation: 8mpTP-4mDBtPBfpm) represented by Structural Formula (ii) above, 9-(2-naphthyl)-9′-phenyl-9H,9′H-3,3′-bicarbazole (abbreviation: PNCCP) represented by Structural Formula (iii) above, and [2-d3-methyl-8-(2-pyridinyl-κN)benzofuro[2,3-b]pyridine-KC]bis[2-(5-d3-methyl-2-pyridinyl-κN2)phenyl-κC]iridium(III) (abbreviation: Ir(5mppy-d3)2(mbfpypy-d3)) represented by Structural Formula (iv) above were deposited by co-evaporation to a thickness of 40 nm such that the weight ratio of 8mpTP-4mDBtPBfpm to PNCCP and Ir(5mppy-d3)2(mbfpypy-d3) was 0.5:0.5:0.1, whereby a first light-emitting layer was formed.
Next, 2-{3-[3-(N-phenyl-9H-carbazol-3-yl)-9H-carbazol-9-yl]phenyl}dibenzo[f,h]quinoxaline (abbreviation: 2mPCCzPDBq) represented by Structural Formula (v) above was deposited by evaporation to a thickness of 10 nm to form a first electron-transport layer.
After the first electron-transport layer was formed, 2,2′-(1,3-phenylene)bis(9-phenyl-1,10-phenanthroline) (abbreviation: mPPhen2P) represented by Structural Formula (ix) above, 4,7-di-1-pyrrolidinyl-1,10-phenanthroline (abbreviation: Pyrrd-Phen) represented by Structural Formula (vii) above, and indium oxide (In2O3) were deposited by co-evaporation to a thickness of 5 nm such that the volume ratio of mPPhen2P to Pyrrd-Phen and In2O3 was 0.5:0.5:0.1, so that a first region was formed. Then, copper phthalocyanine (abbreviation: CuPc) represented by Structural Formula (viii) above was deposited by evaporation to a thickness of 2 nm to form a third region. Furthermore, PCBBiF and OCHD-003 were deposited by co-evaporation to a thickness of 10 nm such that the weight ratio of PCBBiF to OCHD-003 was 1:0.15 to form a second region. Thus, an intermediate layer was formed.
Over the intermediate layer, PCBBiF was deposited by evaporation to a thickness of 55 nm, whereby a second hole-transport layer was formed.
Over the second hole-transport layer, 8mpTP-4mDBtPBfpm, PNCCP, and Ir(5mppy-d3)2(mbfpypy-d3) were deposited by co-evaporation to a thickness of 40 nm such that the weight ratio of 8mpTP-4mDBtPBfpm to PNCCP and Ir(5mppy-d3)2(mbfpypy-d3) was 0.5:0.5:0.1, whereby a second light-emitting layer was formed.
Then, 2mPCCzPDBq was deposited by evaporation to a thickness of 20 nm, and mPPhen2P was further deposited by evaporation to a thickness of 20 nm, whereby a second electron-transport layer was formed.
A sample in which the second electron-transport layer and the components thereunder had been formed was taken out from the vacuum evaporation apparatus and exposed to the air. After that, aluminum oxide was deposited to a thickness of 30 nm by an ALD method using trimethylaluminum (abbreviation: TMA) as a precursor and water vapor as an oxidizer to form a first sacrificial layer.
Next, over the first sacrificial layer, molybdenum was deposited to a thickness of 50 nm by a sputtering method to form a second sacrificial layer.
A resist was formed using a photoresist over the second sacrificial layer, and processing was performed by a lithography technique to form a slit having a width of 3 μm in a position 3.5 μm away from an end portion of the first electrode.
Specifically, the second sacrificial layer was processed using an etching gas containing tetrafluoromethane (CF4), oxygen (O2), and helium (He) at a flow rate ratio of CF4:O2:He=100:67:333 and an etching gas containing oxygen (O2) with the use of the resist as a mask. Then, the first sacrificial layer was processed using a basic chemical solution containing tetramethyl ammonium hydroxide (abbreviation: TMAH) and water as a solvent and an etching gas containing fluoroform (CHF3) and helium (He) at a flow rate ratio of CHF3:He=1:49. After that, the second electron-transport layer, the second light-emitting layer, the second hole-transport layer, the intermediate layer, the first electron-transport layer, the first light-emitting layer, the first hole-transport layer, and the hole-injection layer were processed using an etching gas containing oxygen (O2).
After the processing with the photolithography technique, the second sacrificial layer was removed using an etching gas containing tetrafluoromethane (CF4), oxygen (O2), and helium (He) at a flow rate ratio of CF4:O2:He=100:67:333. Then, the first sacrificial layer was removed using an acidic chemical solution of a mixed acid containing hydrofluoric acid, phosphoric acid, and nitric acid, and water as a solvent, so that the top surface of the second electron-transport layer was exposed. Then, the substrate was transferred into a vacuum evaporation apparatus where the pressure was reduced to approximately 1×10−4 Pa, and heat treatment was performed at 110° C. for one hour in a heating chamber of the vacuum evaporation apparatus.
After that, lithium fluoride (LiF) and ytterbium (Yb) were deposited by co-evaporation to a thickness of 1.5 nm such that the volume ratio of LiF to Yb was 1:0.5, and then silver (Ag) and magnesium (Mg) were deposited by co-evaporation to a thickness of 15 nm such that the volume ratio of Ag to Mg was 1:0.1, whereby the second electrode 102 was formed. Over the second electrode 102, 4,4′,4″-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation: DBT3P-II) represented by Structural Formula (x) above was deposited to a thickness of 70 nm as a cap layer to improve light extraction efficiency.
Then, the light-emitting device was sealed using a glass substrate in a glove box containing a nitrogen atmosphere so as not to be exposed to the air. Specifically, a UV curable sealing material was applied to surround the device, only the sealing material was irradiated with UV while the light-emitting device was not irradiated with the UV, and heat treatment was performed at 80° C. under an atmospheric pressure for one hour. In this manner, the light-emitting device 4 was fabricated.
The comparative light-emitting device 4 was fabricated in a manner similar to that of the light-emitting device 4 except that the second electrode 102 was formed successively after the formation of the second electron-transport layer without processing with the photolithography technique in the fabrication process of the light-emitting device 4.
The light-emitting device 5 was fabricated in a manner similar to that of the light-emitting device 4 except that mPPhen2P in the first region of the light-emitting device 4 was replaced with 2,9-di(naphthalen-2-yl)-4,7-diphenyl-1,10-phenanthroline (abbreviation: NBPhen) represented by Structural Formula (vi) above.
The comparative light-emitting device 5 was fabricated in a manner similar to that of the light-emitting device 5 except that the second electrode 102 was formed successively after the formation of the second electron-transport layer without processing with the photolithography technique in the fabrication process of the light-emitting device 5.
Device structures of the light-emitting devices 4 and 5 and the comparative light-emitting devices 4 and 5 are shown below.
As can be seen from
Since In2O3 is a metal oxide and thus is stable against oxygen and water in the air and water and a chemical solution used during the process, the characteristics thereof do not change much even through a photolithography process involving exposure to the air and water. However, the stability hinders the interaction with an organic compound; hence, In2O3 is not likely to function as a donor like Li.
In contrast, the light-emitting devices 4 and 5 of one embodiment of the present invention, each of which includes In2O3 and Pyrrd-Phen in the first region of the intermediate layer, exhibit favorable characteristics comparable to those of the light-emitting device fabricated by a continuous vacuum process, even though the light-emitting devices 4 and 5 were fabricated through processing with the photolithography technique. This is probably because Pyrrd-Phen has a phenanthroline skeleton with an electron-donating group to increase the electron density of the phenanthroline skeleton, and the interaction between Pyrrd-Phen and Li2O as the metal oxide becomes strong, so that the donor property is improved.
As described above, in the light-emitting device of one embodiment of the present invention, electrons are easily injected and transported from the intermediate layer to the electron-transport layer even when the light-emitting device is processed by the photolithography technique, so that a light-emitting device with a low driving voltage can be obtained.
Unlike an alkali metal and an alkaline earth metal which are easily oxidized in the air, In2O3 is a metal oxide stable in the air and thus can be easily treated without need of special handling. Hence, a light-emitting device using a metal oxide is easy to mass produce and can be manufactured at low cost.
Described in this example are specific methods for fabricating a light-emitting device 6 of one embodiment of the present invention, and a comparative light-emitting device 6-1 to a comparative light-emitting device 6-3, and characteristics of the light-emitting devices. Structural formulae of main compounds used in this example are shown below.
First, 100-nm-thick silver (Ag) and 85-nm-thick indium tin oxide containing silicon oxide (ITSO) were stacked over a glass substrate sequentially from the substrate side by a sputtering method as a reflective electrode and a transparent electrode, respectively, whereby the first electrode 101 with a size of 2 mm×2 mm was formed. Note that the transparent electrode functions as an anode, and the transparent electrode and the reflective electrode are collectively regarded as the first electrode 101.
Next, in pretreatment for forming the light-emitting device over a substrate, the surface of the substrate was washed with water, and baking was performed at 200° C. for one hour.
After that, the substrate was transferred into a vacuum evaporation apparatus where the pressure was reduced to approximately 1×10−4 Pa, and was subjected to vacuum baking at 170° C. for 30 minutes in a heating chamber of the vacuum evaporation apparatus, and then the substrate was cooled down for approximately 30 minutes.
Then, the substrate provided with the first electrode 101 was fixed to a holder provided in the vacuum evaporation apparatus such that the surface on which the first electrode 101 was formed faced downward. Over the first electrode 101, N-(biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H-fluoren-2-amine (abbreviation: PCBBiF) represented by Structural Formula (i) above and an electron-accepting material having 4 or more fluorine atoms and a molecular weight of 672 (OCHD-003) were deposited by co-evaporation to a thickness of 10 nm such that the weight ratio of PCBBiF to OCHD-003 was 1:0.03, whereby the hole-injection layer 111 was formed.
Over the hole-injection layer 111, PCBBiF was deposited by evaporation to a thickness of 90 nm, whereby a first hole-transport layer was formed.
Then, over the first hole-transport layer, 8-(1,1′:4′,1″-terphenyl-3-yl)-4-[3-(dibenzothiophen-4-yl)phenyl]-[1]benzofuro[3,2-d]pyrimidine (abbreviation: 8mpTP-4mDBtPBfpm) represented by Structural Formula (ii) above, 9-(2-naphthyl)-9′-phenyl-9H,9′H-3,3′-bicarbazole (abbreviation: PNCCP) represented by Structural Formula (iii) above, and [2-d3-methyl-8-(2-pyridinyl-κN)benzofuro[2,3-b]pyridine-KC]bis[2-(5-d3-methyl-2-pyridinyl-κN2)phenyl-κC]iridium(III) (abbreviation: Ir(5mppy-d3)2(mbfpypy-d3)) represented by Structural Formula (iv) above were deposited by co-evaporation to a thickness of 40 nm such that the weight ratio of 8mpTP-4mDBtPBfpm to PNCCP and Ir(5mppy-d3)2(mbfpypy-d3) was 0.5:0.5:0.1, whereby a first light-emitting layer was formed.
Next, 2-{3-[3-(N-phenyl-9H-carbazol-3-yl)-9H-carbazol-9-yl]phenyl}dibenzo[f,h]quinoxaline (abbreviation: 2mPCCzPDBq) represented by Structural Formula (v) above was deposited by evaporation to a thickness of 10 nm to form a first electron-transport layer.
After the first electron-transport layer was formed, 2,2′-(1,3-phenylene)bis(9-phenyl-1,10-phenanthroline) (abbreviation: mPPhen2P) represented by Structural Formula (ix) above, 4,7-di-1-pyrrolidinyl-1,10-phenanthroline (abbreviation: Pyrrd-Phen) represented by Structural Formula (vii) above, and indium oxide (In2O3) were deposited by co-evaporation to a thickness of 5 nm such that the volume ratio of mPPhen2P to Pyrrd-Phen and In2O3 was 0.5:0.5:0.1, so that a first region was formed. Then, copper phthalocyanine (abbreviation: CuPc) represented by Structural Formula (viii) above was deposited by evaporation to a thickness of 2 nm to form a third region. Furthermore, PCBBiF and OCHD-003 were deposited by co-evaporation to a thickness of 10 nm such that the weight ratio of PCBBiF to OCHD-003 was 1:0.15 to form a second region. Thus, an intermediate layer was formed.
Over the intermediate layer, PCBBiF was deposited by evaporation to a thickness of 55 nm, whereby a second hole-transport layer was formed.
Over the second hole-transport layer, 8mpTP-4mDBtPBfpm, PNCCP, and Ir(5mppy-d3)2(mbfpypy-d3) were deposited by co-evaporation to a thickness of 40 nm such that the weight ratio of 8mpTP-4mDBtPBfpm to PNCCP and Ir(5mppy-d3)2(mbfpypy-d3) was 0.5:0.5:0.1, whereby a second light-emitting layer was formed.
Then, 2mPCCzPDBq was deposited by evaporation to a thickness of 20 nm, and mPPhen2P was further deposited by evaporation to a thickness of 20 nm, whereby a second electron-transport layer was formed.
A sample in which the second electron-transport layer and the components thereunder had been formed was exposed to an air atmosphere for one hour. After that, the sample was subjected to vacuum baking at 110° C. for one hour in a heating chamber of the vacuum evaporation apparatus where the pressure was reduced to approximately 1×10−4 Pa.
After that, lithium fluoride (LiF) and ytterbium (Yb) were deposited by co-evaporation to a thickness of 1.5 nm such that the volume ratio of LiF to Yb was 1:0.5, and then silver (Ag) and magnesium (Mg) were deposited by co-evaporation to a thickness of 15 nm such that the volume ratio of Ag to Mg was 1:0.1, whereby the second electrode 102 was formed. Over the second electrode 102, 4,4′,4″-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation: DBT3P-II) represented by Structural Formula (x) above was deposited to a thickness of 70 nm as a cap layer to improve light extraction efficiency.
Then, the light-emitting device was sealed using a glass substrate in a glove box containing a nitrogen atmosphere so as not to be exposed to the air. Specifically, a UV curable sealing material was applied to surround the device, only the sealing material was irradiated with UV while the light-emitting device was not irradiated with the UV, and heat treatment was performed at 80° C. under an atmospheric pressure for one hour. In this manner, the light-emitting device 6 was fabricated.
The comparative light-emitting device 6-1 was fabricated in a manner similar to that of the light-emitting device 6 except that the first region of the intermediate layer in the light-emitting device 6 was formed to have a stacked-layer structure of 5-nm-thick mPPhen2P and 2-nm-thick In2O3.
The comparative light-emitting device 6-2 was fabricated in a manner similar to that of the light-emitting device 6 except that the first region of the intermediate layer in the light-emitting device 6 was formed by co-evaporation of mPPhen2P and In2O3 to a thickness of 5 nm such that the volume ratio of mPPhen2P to In2O3 was 1:0.1.
The comparative light-emitting device 6-3 was fabricated in a manner similar to that of the light-emitting device 6 except that the first region of the intermediate layer in the light-emitting device 6 was formed by co-evaporation of 2,9-di(naphthalen-2-yl)-4,7-diphenyl-1,10-phenanthroline (abbreviation: NBPhen) represented by Structural Formula (vi) above and In2O3 to a thickness of 5 nm such that the volume ratio of NBPhen to In2O3 was 1:0.1.
Device structures of the light-emitting device 6 and the comparative light-emitting devices 6-1 to 6-3 are shown below.
The comparative light-emitting device 6-1 in this example is compared with the light-emitting device 1 and the comparative light-emitting device 1-1 in Example 1. The following table shows again main characteristics of the light-emitting device 1, the comparative light-emitting device 1-1, and the comparative light-emitting device 6-1 at approximately 1000 cd/m2.
This result also shows that the tandem light-emitting device including a metal oxide in the first region of the intermediate layer exhibits favorable characteristics by including an organic compound having a phenanthroline ring with an electron-donating group in the first region.
Shown below the results of calculating the work functions and ionization potentials of a single film of In2O3 (Sample 3-1) and a mixed film of In2O3 and an organic compound having a phenanthroline ring with an electron-donating group (Sample 3-2).
Sample 3-1 was obtained as follows: 10-nm-thick aluminum was deposited by evaporation over a quartz substrate in a vacuum evaporation apparatus; 20-nm-thick indium oxide (In2O3) was deposited by evaporation; then, sealing was performed. After transferred into a measurement apparatus, the sample was set in an argon atmosphere and measured in a reduced-pressure atmosphere at approximately 1×10−4 Pa.
Sample 3-2 was obtained as follows: 10-nm-thick aluminum was deposited by evaporation over a quartz substrate in a vacuum evaporation apparatus; mPPhen2P, Pyrrd-Phen, and indium oxide (In2O3) were deposited by co-evaporation to a thickness of 20 nm such that the volume ratio of mPPhen2P to Pyrrd-Phen and In2O3 was 0.5:0.5:0.1; then, sealing was performed. After transferred into a measurement apparatus, the sample was set in an argon atmosphere and measured in a reduced-pressure atmosphere at approximately 1×10−4 Pa.
The measurement was performed by ultraviolet photoelectron spectroscopy (UPS). As a measurement apparatus, VersaProbe manufactured by PHI, Inc. was used. As measurement conditions, an ultraviolet light source was HeI (21.22 eV), the analysis area was 4|800 μm, the analysis depth was approximately 1 nm, and the bias voltage was −10 V.
The work function is calculated by subtracting the absolute value of the difference between Ek(min) and Fermi energy from the energy of irradiation light (hv: 21.22 eV). The ionization potential is calculated by subtracting the absolute value of the difference between Ek(min) and Ek(max) from the energy of irradiation light (21.22 eV). Since the Fermi edge was not observed in this measurement, the work function was obtained on the assumption that the Fermi level Ef was −10.0 eV (a position shifted from 0.0 eV by the applied bias).
As shown above, the mixed film of a metal oxide and an organic compound having a phenanthroline ring with an electron-donating group has a lower work function than the single film of a metal oxide alone, and thus electrons are easily injected into the mixed film. This shows that the first region is preferably a mixed film of a metal oxide and an organic compound having a phenanthroline ring with an electron-donating group.
Described in this example are specific methods for fabricating a light-emitting device 7-1 and a light-emitting device 7-2 of one embodiment of the present invention, and characteristics of the light-emitting devices. The light-emitting devices 7-1 and 7-2 include different metal oxides in a first region of an intermediate layer. Structural formulae of main compounds used in this example are shown below.
First, 100-nm-thick alloy of silver, palladium, and copper (Ag—Pd—Cu, also referred to as APC) and 50-nm-thick indium tin oxide containing silicon oxide (JTSO) were stacked over a glass substrate sequentially from the substrate side by a sputtering method as a reflective electrode and a transparent electrode, respectively, whereby the first electrode 101 with a size of 2 mm×2 mm was formed. Note that the transparent electrode functions as an anode, and the transparent electrode and the reflective electrode are collectively regarded as the first electrode 101.
Next, in pretreatment for forming the light-emitting device over a substrate, the surface of the substrate was washed with water, and baking was performed at 200° C. for one hour.
After that, the substrate was transferred into a vacuum evaporation apparatus where the pressure was reduced to approximately 1×10−4 Pa, and was subjected to vacuum baking at 170° C. for 30 minutes in a heating chamber of the vacuum evaporation apparatus, and then the substrate was cooled down for approximately 30 minutes.
Then, the substrate provided with the first electrode 101 was fixed to a holder provided in the vacuum evaporation apparatus such that the surface on which the first electrode 101 was formed faced downward. Over the first electrode 101, N-(biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H-fluoren-2-amine (abbreviation: PCBBiF) represented by Structural Formula (i) above and an electron-accepting material having 4 or more fluorine atoms and a molecular weight of 672 (OCHD-003) were deposited by co-evaporation to a thickness of 10 nm such that the weight ratio of PCBBiF to OCHD-003 was 1:0.03, whereby the hole-injection layer 111 was formed.
Over the hole-injection layer 111, PCBBiF was deposited by evaporation to a thickness of 125 nm, whereby a first hole-transport layer was formed.
Then, over the first hole-transport layer, 8-(1,1′:4′,1″-terphenyl-3-yl)-4-[3-(dibenzothiophen-4-yl)phenyl]-[1]benzofuro[3,2-d]pyrimidine (abbreviation: 8mpTP-4mDBtPBfpm) represented by Structural Formula (ii) above, 9-(2-naphthyl)-9′-phenyl-9H,9′H-3,3′-bicarbazole (abbreviation: PNCCP) represented by Structural Formula (iii) above, and [2-d3-methyl-8-(2-pyridinyl-κN)benzofuro[2,3-b]pyridine-C]bis[2-(5-d3-methyl-2-pyridinyl-κN2)phenyl-κC]iridium(III) (abbreviation: Ir(5mppy-d3)2(mbfpypy-d3)) represented by Structural Formula (iv) above were deposited by co-evaporation to a thickness of 40 nm such that the weight ratio of 8mpTP-4mDBtPBfpm to PNCCP and Ir(5mppy-d3)2(mbfpypy-d3) was 0.5:0.5:0.1, whereby a first light-emitting layer was formed.
Next, 2-{3-[3-(N-phenyl-9H-carbazol-3-yl)-9H-carbazol-9-yl]phenyl}dibenzo[f,h]quinoxaline (abbreviation: 2mPCCzPDBq) represented by Structural Formula (v) above was deposited by evaporation to a thickness of 10 nm to form a first electron-transport layer.
After the first electron-transport layer was formed, 2,9-di(naphthalen-2-yl)-4,7-diphenyl-1,10-phenanthroline (abbreviation: NBPhen) represented by Structural Formula (vi) above, 4,7-di-1-pyrrolidinyl-1,10-phenanthroline (abbreviation: Pyrrd-Phen) represented by Structural Formula (vii) above, and indium oxide (In2O3) were deposited by co-evaporation to a thickness of 5 nm such that the volume ratio of NBPhen to Pyrrd-Phen and In2O3 was 0.5:0.5:0.1, so that a first region was formed. Then, copper phthalocyanine (abbreviation: CuPc) represented by Structural Formula (viii) above was deposited by evaporation to a thickness of 2 nm to form a third region. Furthermore, PCBBiF and OCHD-003 were deposited by co-evaporation to a thickness of 10 nm such that the weight ratio of PCBBiF to OCHD-003 was 1:0.15 to forma second region. Thus, an intermediate layer was formed.
Over the intermediate layer, PCBBiF was deposited by evaporation to a thickness of 55 nm, whereby a second hole-transport layer was formed.
Over the second hole-transport layer, 8mpTP-4mDBtPBfpm, PNCCP, and Ir(5mppy-d3)2(mbfpypy-d3) were deposited by co-evaporation to a thickness of 40 nm such that the weight ratio of 8mpTP-4mDBtPBfpm to PNCCP and Ir(5mppy-d3)2(mbfpypy-d3) was 0.5:0.5:0.1, whereby a second light-emitting layer was formed.
Then, 2mPCCzPDBq was deposited by evaporation to a thickness of 20 nm, and 2,2′-(1,3-phenylene)bis(9-phenyl-1,10-phenanthroline) (abbreviation: mPPhen2P) represented by Structural Formula (ix) above was further deposited by evaporation to a thickness of 20 nm, whereby a second electron-transport layer was formed.
A sample in which the second electron-transport layer and the components thereunder had been formed was taken out from the vacuum evaporation apparatus and exposed to the air. After that, aluminum oxide was deposited to a thickness of 30 nm by an ALD method using trimethylaluminum (abbreviation: TMA) as a precursor and water vapor as an oxidizer to form a first sacrificial layer.
Next, over the first sacrificial layer, molybdenum was deposited to a thickness of 50 nm by a sputtering method to form a second sacrificial layer.
A resist was formed using a photoresist over the second sacrificial layer, and processing was performed by a lithography technique to form a slit having a width of 3 μm in a position 3.5 μm away from an end portion of the first electrode.
Specifically, the second sacrificial layer was processed using an etching gas containing tetrafluoromethane (CF4), oxygen (O2), and helium (He) at a flow rate ratio of CF4:O2:He=100:67:333 and an etching gas containing oxygen (O2) with the use of the resist as a mask. Then, the first sacrificial layer was processed using a basic chemical solution containing tetramethyl ammonium hydroxide (abbreviation: TMAH) and water as a solvent and an etching gas containing fluoroform (CHF3) and helium (He) at a flow rate ratio of CHF3:He=1:49. After that, the second electron-transport layer, the second light-emitting layer, the second hole-transport layer, the intermediate layer, the first electron-transport layer, the first light-emitting layer, the first hole-transport layer, and the hole-injection layer were processed using an etching gas containing oxygen (O2).
After the processing with the photolithography technique, the second sacrificial layer was removed using an etching gas containing tetrafluoromethane (CF4), oxygen (O2), and helium (He) at a flow rate ratio of CF4:O2:He=100:67:333. Then, the first sacrificial layer was removed using an acidic chemical solution of a mixed acid containing hydrofluoric acid, phosphoric acid, and nitric acid, and water as a solvent, so that the top surface of the second electron-transport layer was exposed. Then, the substrate was transferred into a vacuum evaporation apparatus where the pressure was reduced to approximately 1×10−4 Pa, and heat treatment was performed at 110° C. for one hour in a heating chamber of the vacuum evaporation apparatus.
After that, lithium fluoride (LiF) and ytterbium (Yb) were deposited by co-evaporation to a thickness of 1.5 nm such that the volume ratio of LiF to Yb was 1:0.5, and then silver (Ag) and magnesium (Mg) were deposited by co-evaporation to a thickness of 15 nm such that the volume ratio of Ag to Mg was 1:0.1, whereby the second electrode 102 was formed. Over the second electrode 102, 4,4′,4″-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation: DBT3P-II) represented by Structural Formula (x) above was deposited to a thickness of 70 nm as a cap layer to improve light extraction efficiency.
Then, the light-emitting device was sealed using a glass substrate in a glove box containing a nitrogen atmosphere so as not to be exposed to the air. Specifically, a UV curable sealing material was applied to surround the device, only the sealing material was irradiated with UV while the light-emitting device was not irradiated with the UV, and heat treatment was performed at 80° C. under an atmospheric pressure for one hour. In this manner, the light-emitting device 7-1 was fabricated.
The light-emitting device 7-2 was fabricated in a manner similar to that of the light-emitting device 7-1 except that In2O3 used for forming the first region in the light-emitting device 7-1 was replaced with indium (In).
Device structures of the light-emitting devices 7-1 and 7-2 are shown below. Note that the materials for the first region indicate the materials used in fabricating the devices.
Sample 1-1 was fabricated in the following manner: 2,2′-(1,3-phenylene)bis(9-phenyl-1,10-phenanthroline) (abbreviation: mPPhen2P), 4,7-di-1-pyrrolidinyl-1,10-phenanthroline (abbreviation: Pyrrd-Phen), and indium were deposited over a quartz substrate to a thickness of 50 nm such that the volume ratio of mPPhen2P to Pyrrd-Phen and In was 0.5:0.5:0.1. Sample 1-2 was fabricated in the following manner: mPPhen2P, Pyrrd-Phen, and indium oxide (In2O3) were deposited over a quartz substrate to a thickness of 50 nm such that the volume ratio of mPPhen2P to Pyrrd-Phen and In2O3 was 0.5:0.5:0.1.
The results show that almost all of In in the first region of the light-emitting device 7-2 highly probably exist as indium oxide such as In2O3. For this reason, the light-emitting devices 7-1 and 7-2 may have substantially the same characteristics.
Thus, even when a metal alone is used instead of a metal oxide in formation of the first region and oxidized during formation of the first region, the light-emitting device of one embodiment of the present invention can be obtained.
In the light-emitting device of one embodiment of the present invention, the first region includes a metal oxide and an organic compound having a phenanthroline ring with an electron-donating group; thus, electrons are easily injected and transported from the intermediate layer to the electron-transport layer even when the light-emitting device is processed by the photolithography technique, so that a light-emitting device with a low driving voltage can be obtained.
In this example, samples imitating the first region of the intermediate layer of the light-emitting device of one embodiment of the present invention were evaluated by an electron spin resonance method, and the evaluation results are described.
First, methods for fabricating the samples used in this example are described.
First, a quartz substrate was fixed to a holder in a vacuum evaporation apparatus such that the surface to be subjected to evaporation faced downward. Next, the pressure in the vacuum evaporation apparatus was reduced to 1×10−4 Pa and then, mPPhen2P, Pyrrd-Phen, and In2O3 were deposited by co-evaporation to a thickness of 50 nm such that the volume ratio of mPPhen2P to Pyrrd-Phen and In2O3 was 0.5:0.5:0.02, whereby Sample 2-1 was fabricated. The size of the quartz substrate was 3.0 mm×20 mm. Note that the measurement was performed by stacking four samples fabricated in the above manner to have a thickness of 200 nm when spin density was calculated.
Sample 2-2 was fabricated by replacing In2O3 used in Sample 2-1 with Li2O. The other conditions were similar to those of Sample 2-1. Note that the measurement was performed by stacking four samples fabricated in the above manner to have a thickness of 200 nm when spin density was calculated.
Sample 2-3 was fabricated by omitting In2O3 from Sample 2-1. Sample 2-3 was fabricated by depositing Pyrrd-Phen and mPPhen2P by co-evaporation to a thickness of 50 nm such that the weight ratio of Pyrrd-Phen to mPPhen2P was 0.5:0.5. The other conditions were similar to those of Sample 2-1. Note that the measurement was performed by stacking four samples fabricated in the above manner to have a thickness of 200 nm when spin density was calculated.
A quartz substrate was fixed to a holder in a vacuum evaporation apparatus such that the surface to be subjected to evaporation faced downward. Next, the pressure in the vacuum evaporation apparatus was reduced to 1×10−4 Pa and then, Pyrrd-Phen was deposited by evaporation to a thickness of 50 nm, whereby Sample 2-4 was fabricated. The size of the quartz substrate was 3.0 mm×20 mm. Note that the measurement was performed by stacking four samples fabricated in the above manner to have a thickness of 200 nm when spin density was calculated.
Sample 2-5 was fabricated in a manner similar to that of Sample 2-4 except that Pyrrd-Phen was replaced with mPPhen2P. Note that the measurement was performed by stacking four samples fabricated in the above manner to have a thickness of 200 nm when spin density was calculated.
A quartz substrate was fixed to a holder in a vacuum evaporation apparatus such that the surface to be subjected to evaporation faced downward. Next, the pressure in the vacuum evaporation apparatus was reduced to 1×10−4 Pa and then, In2O3 was deposited by evaporation to a thickness of 28 nm, whereby Sample 2-6 was fabricated. The size of the quartz substrate was 3.0 mm×20 mm. Note that the measurement was performed by stacking four samples fabricated in the above manner to have a thickness of 112 nm when spin density was calculated.
The fabricated samples were evaluated by an ESR method. Note that the measurement of the electron spin resonance spectrum using an ESR method was performed with an electron spin resonance spectrometer E500 (manufactured by Bruker Corporation). The measurement was performed at room temperature under the conditions where the resonance frequency was 9.56 GHz, the output power was 1 mW, the modulated magnetic field was 50 mT, the modulation width was 0.5 mT, the time constant was 0.04 s, and the sweep time was 1 min.
Similarly, PCBBiF and OCHD-003 were deposited by co-evaporation to a thickness of 100 nm over a quartz substrate such that the weight ratio of PCBBiF to OCHD-003 was 1:0.1. Two samples of such a thin film were stacked to have a thickness of 200 nm, and the electron spin resonance spectrum thereof was measured at room temperature. The measurement of the electron spin resonance spectrum using an ESR method was performed with an electron spin resonance spectrometer JES FA300 (manufactured by JEOL Ltd.). The measurement was performed at room temperature under the conditions where the resonance frequency was 9.18 GHz, the output power was 1 mW, the modulated magnetic field was 50 mT, the modulation width was 0.5 mT, the time constant was 0.03 s, and the sweep time was 1 min. The results are shown in
Described in this example are specific methods for fabricating a light-emitting device 8 of one embodiment of the present invention a comparative light-emitting device 8, and characteristics of the light-emitting devices. Structural formulae of main compounds used in this example are shown below.
First, 100-nm-thick alloy of silver, palladium, and copper (Ag—Pd—Cu, also referred to as APC) and 50-nm-thick indium tin oxide containing silicon oxide (JTSO) were stacked over a glass substrate sequentially from the substrate side by a sputtering method as a reflective electrode and a transparent electrode, respectively, whereby the first electrode 101 with a size of 2 mm×2 mm was formed. Note that the transparent electrode functions as an anode, and the transparent electrode and the reflective electrode are collectively regarded as the first electrode 101.
Next, in pretreatment for forming the light-emitting device over a substrate, the surface of the substrate was washed with water, and baking was performed at 200° C. for one hour.
After that, the substrate was transferred into a vacuum evaporation apparatus where the pressure was reduced to approximately 1×10−4 Pa, and was subjected to vacuum baking at 170° C. for 30 minutes in a heating chamber of the vacuum evaporation apparatus, and then the substrate was cooled down for approximately 30 minutes.
Then, the substrate provided with the first electrode 101 was fixed to a holder provided in the vacuum evaporation apparatus such that the surface on which the first electrode 101 was formed faced downward. Over the first electrode 101, N-(biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H-fluoren-2-amine (abbreviation: PCBBiF) represented by Structural Formula (i) above and an electron-accepting material having fluorine and a molecular weight of 672 (OCHD-003) were deposited by co-evaporation to a thickness of 10 nm such that the weight ratio of PCBBiF to OCHD-003 was 1:0.03, whereby the hole-injection layer 111 was formed.
Over the hole-injection layer 111, PCBBiF was deposited by evaporation to a thickness of 120 nm, whereby a first hole-transport layer was formed.
Then, over the first hole-transport layer, 8-(1,1′:4′,1″-terphenyl-3-yl)-4-[3-(dibenzothiophen-4-yl)phenyl]-[1]benzofuro[3,2-d]pyrimidine (abbreviation: 8mpTP-4mDBtPBfpm) represented by Structural Formula (ii) above, 9-(2-naphthyl)-9′-phenyl-9H,9′H-3,3′-bicarbazole (abbreviation: PNCCP) represented by Structural Formula (iii) above, and [2-d3-methyl-8-(2-pyridinyl-κN)benzofuro[2,3-b]pyridine-KC]bis[2-(5-d3-methyl-2-pyridinyl-κN2)phenyl-κC]iridium(III) (abbreviation: Ir(5mppy-d3)2(mbfpypy-d3)) represented by Structural Formula (iv) above were deposited by co-evaporation to a thickness of 40 nm such that the weight ratio of 8mpTP-4mDBtPBfpm to PNCCP and Ir(5mppy-d3)2(mbfpypy-d3) was 0.5:0.5:0.1, whereby a first light-emitting layer was formed.
Next, 2-{3-[3-(N-phenyl-9H-carbazol-3-yl)-9H-carbazol-9-yl]phenyl}dibenzo[f,h]quinoxaline (abbreviation: 2mPCCzPDBq) represented by Structural Formula (v) above was deposited by evaporation to a thickness of 10 nm to form a first electron-transport layer.
After the first electron-transport layer was formed, 2,2′-(1,3-phenylene)bis(9-phenyl-1,10-phenanthroline) (abbreviation: mPPhen2P) represented by Structural Formula (ix) above, 4,7-di(2,3,3a,4,5,6,7,7a-octahydro-1H-isoindol-2-yl)-1,10-phenanthroline (abbreviation: Hid2Phen) represented by Structural Formula (xiii) above, and lithium oxide (Li2O) were deposited by co-evaporation to a thickness of 5 nm such that the volume ratio of mPPhen2P to Hid2Phen and Li2O was 0.5:0.5:0.02, so that a first region was formed. Then, copper phthalocyanine (abbreviation: CuPc) represented by Structural Formula (viii) above was deposited by evaporation to a thickness of 2 nm to form a third region. Furthermore, PCBBiF and OCHD-003 were deposited by co-evaporation to a thickness of 10 nm such that the weight ratio of PCBBiF to OCHD-003 was 1:0.15 to form a second region. Thus, an intermediate layer was formed.
Over the intermediate layer, PCBBiF was deposited by evaporation to a thickness of 50 nm, whereby a second hole-transport layer was formed.
Over the second hole-transport layer, 8mpTP-4mDBtPBfpm, PNCCP, and Ir(5mppy-d3)2(mbfpypy-d3) were deposited by co-evaporation to a thickness of 40 nm such that the weight ratio of 8mpTP-4mDBtPBfpm to PNCCP and Ir(5mppy-d3)2(mbfpypy-d3) was 0.5:0.5:0.1, whereby a second light-emitting layer was formed.
Then, 2mPCCzPDBq was deposited by evaporation to a thickness of 20 nm, and mPPhen2P was further deposited by evaporation to a thickness of 20 nm, whereby a second electron-transport layer was formed.
A sample in which the second electron-transport layer and the components thereunder had been formed was taken out from the vacuum evaporation apparatus and exposed to the air. After that, aluminum oxide was deposited to a thickness of 30 nm by an ALD method using trimethylaluminum (abbreviation: TMA) as a precursor and water vapor as an oxidizer to form a first sacrificial layer.
Next, over the first sacrificial layer, molybdenum was deposited to a thickness of 50 nm by a sputtering method to form a second sacrificial layer.
A resist was formed using a photoresist over the second sacrificial layer, and processing was performed by a lithography technique to form a slit having a width of 3 μm in a position 3.5 μm away from an end portion of the first electrode.
Specifically, the second sacrificial layer was processed using an etching gas containing tetrafluoromethane (CF4), oxygen (O2), and helium (He) at a flow rate ratio of CF4:O2:He=100:67:333 and an etching gas containing oxygen (O2) with the use of the resist as a mask. Then, the first sacrificial layer was processed using a basic chemical solution containing tetramethyl ammonium hydroxide (abbreviation: TMAH) and water as a solvent and an etching gas containing fluoroform (CHF3) and helium (He) at a flow rate ratio of CHF3:He=1:49. After that, the second electron-transport layer, the second light-emitting layer, the second hole-transport layer, the intermediate layer, the first electron-transport layer, the first light-emitting layer, the first hole-transport layer, and the hole-injection layer were processed using an etching gas containing oxygen (O2).
After the processing with the photolithography technique, the second sacrificial layer was removed using an etching gas containing CF4, O2, and He at a flow rate ratio of CF4:O2:He=100:67:333. Then, the first sacrificial layer was removed using an acidic chemical solution containing water as a solvent, so that the top surface of the second electron-transport layer was exposed. Then, the substrate was transferred into a vacuum evaporation apparatus where the pressure was reduced to approximately 1×10−4 Pa, and heat treatment was performed at 90° C. for one hour in a heating chamber of the vacuum evaporation apparatus.
After that, lithium fluoride (LiF) and ytterbium (Yb) were deposited by co-evaporation to a thickness of 1.5 nm such that the volume ratio of LiF to Yb was 1:0.5, and then silver (Ag) and magnesium (Mg) were deposited by co-evaporation to a thickness of 15 nm such that the volume ratio of Ag to Mg was 1:0.1, whereby the second electrode 102 was formed. Over the second electrode 102, 4,4′,4″-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation: DBT3P-II) represented by Structural Formula (x) above was deposited to a thickness of 70 nm as a cap layer to improve light extraction efficiency.
Then, the light-emitting device was sealed using a glass substrate in a glove box containing a nitrogen atmosphere so as not to be exposed to the air. Specifically, a UV curable sealing material was applied to surround the device, only the sealing material was irradiated with UV while the light-emitting device was not irradiated with the UV, and heat treatment was performed at 80° C. under an atmospheric pressure for one hour. In this manner, the light-emitting device 8 was fabricated.
The comparative light-emitting device 8 was fabricated in a manner similar to that of the light-emitting device 8 except that the second electrode 102 was formed successively after the formation of the second electron-transport layer without processing with the photolithography technique in the fabrication process of the light-emitting device 8.
Device structures of the light-emitting device 8 and the comparative light-emitting device 8 are shown below.
As can be seen from
As described above, in the light-emitting device of one embodiment of the present invention, electrons are easily injected and transported from the intermediate layer to the electron-transport layer even when the light-emitting device is processed by the photolithography technique, so that a light-emitting device with a low driving voltage can be obtained.
Described in this example are specific methods for fabricating a light-emitting device 9 of one embodiment of the present invention, and characteristics of the light-emitting device. Structural formulae of main compounds used in this example are shown below.
First, 100-nm-thick silver (Ag) and 85-nm-thick indium tin oxide containing silicon oxide (ITSO) were stacked over a glass substrate sequentially from the substrate side by a sputtering method as a reflective electrode and a transparent electrode, respectively, whereby the first electrode 101 with a size of 2 mm×2 mm was formed. Note that the transparent electrode functions as an anode, and the transparent electrode and the reflective electrode are collectively regarded as the first electrode 101.
Next, in pretreatment for forming the light-emitting device over a substrate, the surface of the substrate was washed with water, and baking was performed at 200° C. for one hour.
After that, the substrate was transferred into a vacuum evaporation apparatus where the pressure was reduced to approximately 1×10−4 Pa, and was subjected to vacuum baking at 170° C. for 30 minutes in a heating chamber of the vacuum evaporation apparatus, and then the substrate was cooled down for approximately 30 minutes.
Then, the substrate provided with the first electrode 101 was fixed to a holder provided in the vacuum evaporation apparatus such that the surface on which the first electrode 101 was formed faced downward. Over the first electrode 101, N-(biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H-fluoren-2-amine (abbreviation: PCBBiF) represented by Structural Formula (i) above and an electron-accepting material having fluorine and a molecular weight of 672 (OCHD-003) were deposited by co-evaporation to a thickness of 10 nm such that the weight ratio of PCBBiF to OCHD-003 was 1:0.03, whereby the hole-injection layer 111 was formed.
Over the hole-injection layer 111, PCBBiF was deposited by evaporation to a thickness of 85 nm, whereby a first hole-transport layer was formed.
Then, over the first hole-transport layer, 8-(1,1′:4′,1″-terphenyl-3-yl)-4-[3-(dibenzothiophen-4-yl)phenyl]-[1]benzofuro[3,2-d]pyrimidine (abbreviation: 8mpTP-4mDBtPBfpm) represented by Structural Formula (ii) above, 9-(2-naphthyl)-9′-phenyl-9H,9′H-3,3′-bicarbazole (abbreviation: PNCCP) represented by Structural Formula (iii) above, and [2-d3-methyl-8-(2-pyridinyl-κN)benzofuro[2,3-b]pyridine-KC]bis[2-(5-d3-methyl-2-pyridinyl-κN2)phenyl-κC]iridium(III) (abbreviation: Ir(5mppy-d3)2(mbfpypy-d3)) represented by Structural Formula (iv) above were deposited by co-evaporation to a thickness of 40 nm such that the weight ratio of 8mpTP-4mDBtPBfpm to PNCCP and Ir(5mppy-d3)2(mbfpypy-d3) was 0.5:0.5:0.1, whereby a first light-emitting layer was formed.
Next, 2-{3-[3-(N-phenyl-9H-carbazol-3-yl)-9H-carbazol-9-yl]phenyl}dibenzo[f,h]quinoxaline (abbreviation: 2mPCCzPDBq) represented by Structural Formula (v) above was deposited by evaporation to a thickness of 10 nm to form a first electron-transport layer.
After the first electron-transport layer was formed, 2,9-di(naphthalen-2-yl)-4,7-diphenyl-1,10-phenanthroline (abbreviation: NBPhen) represented by Structural Formula (vi) above, 4,7-dimethoxy-1,10-phenanthroline (abbreviation: p-MeO-Phen) represented by Structural Formula (xiv) above, and lithium oxide (Li2O) were deposited by co-evaporation to a thickness of 5 nm such that the volume ratio of NBPhen to p-MeO-Phen and Li2O was 0.5:0.5:0.02, so that a first region was formed. Then, copper phthalocyanine (abbreviation: CuPc) represented by Structural Formula (viii) above was deposited by evaporation to a thickness of 2 nm to form a third region. Furthermore, PCBBiF and OCHD-003 were deposited by co-evaporation to a thickness of 10 nm such that the weight ratio of PCBBiF to OCHD-003 was 1:0.15 to forma second region. Thus, an intermediate layer was formed.
Over the intermediate layer, PCBBiF was deposited by evaporation to a thickness of 50 nm, whereby a second hole-transport layer was formed.
Over the second hole-transport layer, 8mpTP-4mDBtPBfpm, PNCCP, and Ir(5mppy-d3)2(mbfpypy-d3) were deposited by co-evaporation to a thickness of 40 nm such that the weight ratio of 8mpTP-4mDBtPBfpm to PNCCP and Ir(5mppy-d3)2(mbfpypy-d3) was 0.5:0.5:0.1, whereby a second light-emitting layer was formed.
Then, 2mPCCzPDBq was deposited by evaporation to a thickness of 20 nm, and 2,2′-(1,3-phenylene)bis(9-phenyl-1,10-phenanthroline) (abbreviation: mPPhen2P) represented by Structural Formula (ix) above was further deposited by evaporation to a thickness of 20 nm, whereby a second electron-transport layer was formed.
A sample in which the second electron-transport layer and the components thereunder had been formed was exposed to an air atmosphere for one hour. After that, the sample was subjected to vacuum baking at 80° C. for one hour in a heating chamber of the vacuum evaporation apparatus where the pressure was reduced to approximately 1×10−4 Pa.
After that, lithium fluoride (LiF) and ytterbium (Yb) were deposited by co-evaporation to a thickness of 1.5 nm such that the volume ratio of LiF to Yb was 1:0.5, and then silver (Ag) and magnesium (Mg) were deposited by co-evaporation to a thickness of 15 nm such that the volume ratio of Ag to Mg was 1:0.1, whereby the second electrode 102 was formed. Over the second electrode 102, 4,4′,4″-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation: DBT3P-II) represented by Structural Formula (x) above was deposited to a thickness of 70 nm as a cap layer to improve light extraction efficiency.
Then, the light-emitting device was sealed using a glass substrate in a glove box containing a nitrogen atmosphere so as not to be exposed to the air. Specifically, a UV curable sealing material was applied to surround the device, only the sealing material was irradiated with UV while the light-emitting device was not irradiated with the UV, and heat treatment was performed at 80° C. under an atmospheric pressure for one hour. In this manner, the light-emitting device 9 was fabricated.
A device structure of the light-emitting device 9 is shown below.
Described in this example are specific methods for fabricating a light-emitting device 10-1 and a light-emitting device 10-2 of one embodiment of the present invention, and characteristics of the light-emitting devices. Structural formulae of main compounds used in this example are shown below.
First, 100-nm-thick silver (Ag) and 85-nm-thick indium tin oxide containing silicon oxide (ITSO) were stacked over a glass substrate sequentially from the substrate side by a sputtering method as a reflective electrode and a transparent electrode, respectively, whereby the first electrode 101 with a size of 2 mm×2 mm was formed. Note that the transparent electrode functions as an anode, and the transparent electrode and the reflective electrode are collectively regarded as the first electrode 101.
Next, in pretreatment for forming the light-emitting device over a substrate, the surface of the substrate was washed with water, and baking was performed at 200° C. for one hour.
After that, the substrate was transferred into a vacuum evaporation apparatus where the pressure was reduced to approximately 1×10−4 Pa, and was subjected to vacuum baking at 170° C. for 30 minutes in a heating chamber of the vacuum evaporation apparatus, and then the substrate was cooled down for approximately 30 minutes.
Then, the substrate provided with the first electrode 101 was fixed to a holder provided in the vacuum evaporation apparatus such that the surface on which the first electrode 101 was formed faced downward. Over the first electrode 101, N-(biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H-fluoren-2-amine (abbreviation: PCBBiF) represented by Structural Formula (i) above and an electron-accepting material having fluorine and a molecular weight of 672 (OCHD-003) were deposited by co-evaporation to a thickness of 10 nm such that the weight ratio of PCBBiF to OCHD-003 was 1:0.03, whereby the hole-injection layer 111 was formed.
Over the hole-injection layer 111, PCBBiF was deposited by evaporation to a thickness of 90 nm, whereby a first hole-transport layer was formed.
Then, over the first hole-transport layer, 8-(1,1′:4′,1″-terphenyl-3-yl)-4-[3-(dibenzothiophen-4-yl)phenyl]-[1]benzofuro[3,2-d]pyrimidine (abbreviation: 8mpTP-4mDBtPBfpm) represented by Structural Formula (ii) above, 9-(2-naphthyl)-9′-phenyl-9H,9′H-3,3′-bicarbazole (abbreviation: PNCCP) represented by Structural Formula (iii) above, and [2-d3-methyl-8-(2-pyridinyl-κN)benzofuro[2,3-b]pyridine-KC]bis[2-(5-d3-methyl-2-pyridinyl-κN2)phenyl-κC]iridium(III) (abbreviation: Ir(5mppy-d3)2(mbfpypy-d3)) represented by Structural Formula (iv) above were deposited by co-evaporation to a thickness of 40 nm such that the weight ratio of 8mpTP-4mDBtPBfpm to PNCCP and Ir(5mppy-d3)2(mbfpypy-d3) was 0.5:0.5:0.1, whereby a first light-emitting layer was formed.
Next, 2-{3-[3-(N-phenyl-9H-carbazol-3-yl)-9H-carbazol-9-yl]phenyl}dibenzo[f,h]quinoxaline (abbreviation: 2mPCCzPDBq) represented by Structural Formula (v) above was deposited by evaporation to a thickness of 10 nm to form a first electron-transport layer.
After the first electron-transport layer was formed, 2,2′-(1,3-phenylene)bis(9-phenyl-1,10-phenanthroline) (abbreviation: mPPhen2P) represented by Structural Formula (ix) above, 4,7-di-1-pyrrolidinyl-1,10-phenanthroline (abbreviation: Pyrrd-Phen) represented by Structural Formula (vii) above, and indium oxide (In2O3) were deposited by co-evaporation to a thickness of 5 nm such that the volume ratio of mPPhen2P to Pyrrd-Phen and In2O3 was 0.5:0.5:0.1, so that a first region was formed. Then, copper phthalocyanine (abbreviation: CuPc) represented by Structural Formula (viii) above was deposited by evaporation to a thickness of 2 nm to form a third region. Furthermore, PCBBiF and molybdenum(VI) oxide (abbreviation: MoO3) were deposited by co-evaporation to a thickness of 10 nm such that the weight ratio of PCBBiF to MoO3 was 1:0.5 to form a second region. Thus, an intermediate layer was formed.
Over the intermediate layer, PCBBiF was deposited by evaporation to a thickness of 55 nm, whereby a second hole-transport layer was formed.
Over the second hole-transport layer, 8mpTP-4mDBtPBfpm, PNCCP, and Ir(5mppy-d3)2(mbfpypy-d3) were deposited by co-evaporation to a thickness of 40 nm such that the weight ratio of 8mpTP-4mDBtPBfpm to PNCCP and Ir(5mppy-d3)2(mbfpypy-d3) was 0.5:0.5:0.1, whereby a second light-emitting layer was formed.
Then, 2mPCCzPDBq was deposited by evaporation to a thickness of 20 nm, and mPPhen2P was further deposited by evaporation to a thickness of 20 nm, whereby a second electron-transport layer was formed.
A sample in which the second electron-transport layer and the components thereunder had been formed was exposed to an air atmosphere for one hour. After that, the sample was subjected to vacuum baking at 100° C. for one hour in a heating chamber of the vacuum evaporation apparatus where the pressure was reduced to approximately 1×10−4 Pa.
After that, lithium fluoride (LiF) and ytterbium (Yb) were deposited by co-evaporation to a thickness of 1.5 nm such that the volume ratio of LiF to Yb was 1:0.5, and then silver (Ag) and magnesium (Mg) were deposited by co-evaporation to a thickness of 15 nm such that the volume ratio of Ag to Mg was 1:0.1, whereby the second electrode 102 was formed. Over the second electrode 102, 4,4′,4″-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation: DBT3P-II) represented by Structural Formula (x) above was deposited to a thickness of 70 nm as a cap layer to improve light extraction efficiency.
Then, the light-emitting device was sealed using a glass substrate in a glove box containing a nitrogen atmosphere so as not to be exposed to the air. Specifically, a UV curable sealing material was applied to surround the device, only the sealing material was irradiated with UV while the light-emitting device was not irradiated with the UV, and heat treatment was performed at 80° C. under an atmospheric pressure for one hour. In this manner, the light-emitting device 10-1 was fabricated.
The light-emitting device 10-2 was fabricated in a manner similar to that of the light-emitting device 10-1 except that PCBBiF in the second region was replaced with DBT3P-II in the fabrication process of the light-emitting device 10-1.
Device structures of the light-emitting devices 10-1 and 10-2 are shown below.
This application is based on Japanese Patent Application Serial No. 2023-107919 filed with Japan Patent Office on Jun. 30, 2023, the entire contents of which are hereby incorporated by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2023-107919 | Jun 2023 | JP | national |
