Patent Application
20240206220
One embodiment of the present invention relates to a light-emitting device.
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. 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 proceeding. 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.
Development is extensively 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 a carrier-generation layer in an intermediate layer of a tandem light-emitting device, which includes 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 electron-injection layer or the carrier-generation layer when the surface of the EL layer is exposed to the atmosphere.
However, processing steps with the aforementioned photolithography technique inevitably expose the surface of the EL layer to the atmosphere.
Instead of the alkali metal, the alkaline earth metal, or the compound thereof described above, 1,1′-pyridine-2,6-diyl-bis(1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine) (abbreviation: hpp2Py) is known as an organic compound that can be used in the electron-injection layer (see Patent Document 2, for example). Since hpp2Py is less likely to deteriorate even when being exposed to the atmosphere unlike the alkali metal, the alkaline earth metal, or the compound thereof, hpp2Py used in a light-emitting device formed through a processing step by a photolithography technique involving exposure to the atmosphere does not easily deteriorate.
However, the contact of hpp2Py with a metal such as aluminum induces the electron-injection property; thus, hpp2Py has been hard to use for an intermediate layer of a tandem light-emitting device because of a problem of metal contamination or light transmission.
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 novel light-emitting device having a tandem structure. An object of another embodiment of the present invention is to provide a highly reliable novel 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 novel 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 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 reliable 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 high-emission-efficiency and highly reliable 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 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 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 reliable 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 high-emission-efficiency and highly reliable 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 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.
Other objects are to provide a novel organic compound, a novel light-emitting device, a novel display apparatus, a novel display module, and a novel electronic device.
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 including a first electrode, a second electrode, and an organic compound layer. The organic compound layer is positioned between the first electrode and the second electrode; the organic compound layer includes a first light-emitting unit, a second light-emitting unit, and an intermediate layer; the intermediate layer is positioned between the first light-emitting unit and the second light-emitting unit; the first light-emitting unit is positioned between the first electrode and the intermediate layer; the first light-emitting unit includes a first light-emitting layer and a first electron-transport layer; the first electron-transport layer is in contact with the intermediate layer; the intermediate layer is configured to block holes moving from the first electrode side to the second electrode side; and the first electron-transport layer is a layer having a bipolar property. Another embodiment of the present invention is the light-emitting device having the above-described structure, in which the second light-emitting unit includes a second light-emitting layer.
Another embodiment of the present invention is a light-emitting device including a first electrode, a second electrode, and an organic compound layer. The organic compound layer is positioned between the first electrode and the second electrode; the organic compound layer includes a first light-emitting unit, a second light-emitting unit, and an intermediate layer; the intermediate layer is positioned between the first light-emitting unit and the second light-emitting unit; the first light-emitting unit is positioned between the first electrode and the intermediate layer; the first light-emitting unit includes a first light-emitting layer and a first electron-transport layer; the first electron-transport layer is in contact with the intermediate layer; the intermediate layer is configured to block holes moving from the first electrode side to the second electrode side; and a HOMO level of an organic compound having the highest HOMO level among organic compounds included in the first electron-transport layer is greater than or equal to −5.90 eV and less than or equal to −5.00 eV. Another embodiment of the present invention is the light-emitting device having the above-described structure, in which the second light-emitting unit includes a second light-emitting layer.
Another embodiment of the present invention is a light-emitting device including a first electrode, a second electrode, and an organic compound layer. The organic compound layer is positioned between the first electrode and the second electrode; the organic compound layer includes a first light-emitting unit, a second light-emitting unit, and an intermediate layer; the intermediate layer is positioned between the first light-emitting unit and the second light-emitting unit; the first light-emitting unit is positioned between the first electrode and the intermediate layer; the first light-emitting unit includes a first light-emitting layer and a first electron-transport layer; the first electron-transport layer is in contact with the intermediate layer; the intermediate layer includes an organic compound having strong basicity with an acid dissociation constant pKa of 8 or more; and a HOMO level of an organic compound having the highest HOMO level among organic compounds included in the first electron-transport layer is greater than or equal to −5.90 eV and less than or equal to −5.00 eV. Another embodiment of the present invention is the light-emitting device having the above-described structure, in which the second light-emitting unit includes a second light-emitting layer.
Another embodiment of the present invention is a light-emitting device including a first electrode, a second electrode, and an organic compound layer. The organic compound layer is positioned between the first electrode and the second electrode; the organic compound layer includes a first light-emitting unit, a second light-emitting unit, and an intermediate layer; the intermediate layer is positioned between the first light-emitting unit and the second light-emitting unit; the first light-emitting unit is positioned between the first electrode and the intermediate layer; the first light-emitting unit includes a first light-emitting layer and a first electron-transport layer; the intermediate layer includes a first layer and a second layer; the first layer is in contact with the first electron-transport layer; the first layer includes an organic compound having strong basicity with an acid dissociation constant pKa of 8 or more; the second layer includes an organic compound having a hole-transport property and a substance having an acceptor property with respect to the organic compound having the hole-transport property; and a HOMO level of an organic compound having the highest HOMO level among organic compounds included in the first electron-transport layer is greater than or equal to −5.90 eV and less than or equal to −5.00 eV. Another embodiment of the present invention is the light-emitting device having the above-described structure, in which the second light-emitting unit includes a second light-emitting layer.
Another embodiment of the present invention is the light-emitting device having the above-described structure, in which a LUMO level of an organic compound having the lowest LUMO level among organic compounds included in the first layer is higher than a LUMO level of the substance having an acceptor property with respect to the organic compound having the hole-transport property by 1.0 eV or greater.
Another embodiment of the present invention is the light-emitting device having the above-described structure, in which the light-emitting layers each include a light-emitting material and a host material. The HOMO level of the organic compound having the highest HOMO level among the organic compounds included in the first electron-transport layer is between a HOMO level of the host material and a HOMO level of the organic compound having strong basicity with an acid dissociation constant pKa of 8 or more.
Another embodiment of the present invention is the light-emitting device having the above-described structure, in which a LUMO level of an organic compound having the lowest LUMO level among organic compounds included in the first electron-transport layer is greater than or equal to −3.15 eV and less than or equal to −2.50 eV.
Another embodiment of the present invention is the light-emitting device having the above-described structure, in which the first electron-transport layer includes an organic compound having an electron-transport skeleton and an organic compound having a hole-transport skeleton.
Another embodiment of the present invention is the light-emitting device having the above-described structure, in which the electron-transport skeleton is a π-electron deficient heteroaromatic ring, and the hole-transport skeleton is a π-electron rich heteroaromatic ring.
Another embodiment of the present invention is the light-emitting device having the above-described structure, in which the first electron-transport layer includes an organic compound having an electron-transport skeleton and a hole-transport skeleton.
Another embodiment of the present invention is the light-emitting device having the above-described structure, in which the electron-transport skeleton is a π-electron deficient heteroaromatic ring, and the hole-transport skeleton is a π-electron rich heteroaromatic ring.
Another embodiment of the present invention is the light-emitting device having the above-described structure, in which the hole-transport skeleton is a carbazole skeleton or an amine skeleton.
Another embodiment of the present invention is the light-emitting device having the above-described structure, in which the thickness of the first electron-transport layer is greater than or equal to 2 nm and less than or equal to 13 nm.
Another embodiment of the present invention is the light-emitting device having the above-described structure, in which the thickness of the first electron-transport layer is greater than or equal to 5 nm and less than or equal to 10 nm.
Another embodiment of the present invention is the light-emitting device having the above-described structure, in which the organic compound having strong basicity with an acid dissociation constant pKa of 8 or more does not have an electron-transport skeleton.
Another embodiment of the present invention is the light-emitting device having the above-described structure, in which the organic compound having strong basicity with an acid dissociation constant pKa of 8 or more does not have a π-electron deficient heteroaromatic ring.
Another embodiment of the present invention is the light-emitting device having the above-described structure, in which the organic compound having strong basicity with an acid dissociation constant pKa of 8 or more has a pyrrolidine skeleton, a piperidine skeleton, or a hexahydropyrimidopyrimidine skeleton.
Another embodiment of the present invention is the light-emitting device having the above-described structure, in which the organic compound having strong basicity with an acid dissociation constant pKa of 8 or more has a guanidine skeleton.
Another embodiment of the present invention is the light-emitting device having the above-described structure, in which the organic compound having strong basicity with an acid dissociation constant pKa of 8 or more has a 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine skeleton.
Another embodiment of the present invention is the light-emitting device having the above-described structure, in which the first layer includes the organic compound having strong basicity with an acid dissociation constant pKa of 8 or more and an organic compound having an electron-transport property.
Another embodiment of the present invention is the light-emitting device having the above-described structure, in which the organic compound having strong basicity with an acid dissociation constant pKa of 8 or more does not have an electron-donating property with respect to the organic compound having the electron-transport property.
Another embodiment of the present invention is the light-emitting device having the above-described structure, in which the first layer has a spin density measured by electron spin resonance spectroscopy of lower than or equal to 1×1017 spins/cm3, preferably lower than or equal to 1×1016 spins/cm3.
Another embodiment of the present invention is the light-emitting device having the above-described structure, in which the second layer is a carrier-generation layer. Another embodiment of the present invention is the light-emitting device having the above-described structure, in which the organic compound having the electron-transport property has a π-electron deficient heteroaromatic ring.
Another embodiment of the present invention is the light-emitting device having the above-described structure, in which a LUMO level of the organic compound having the electron-transport property is greater than or equal to −3.0 eV and less than or equal to −2.0 eV.
Another embodiment of the present invention is a display module including the above-described light-emitting device 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 light-emitting device 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 novel light-emitting device having a tandem structure can be provided. With another embodiment of the present invention, a highly reliable novel light-emitting device having a tandem structure can be provided. With another embodiment of the present invention, a highly efficient and highly reliable novel 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 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 reliable 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 high-emission-efficiency and highly reliable 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 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 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 reliable 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 and highly reliable novel light-emitting device that has a tandem structure and can be used in a high-resolution display apparatus can be provided.
With one embodiment of the present invention, a high-resolution and high-emission-efficiency display apparatus can be provided. With one embodiment of the present invention, a high-definition display apparatus with favorable display performance can be provided. With one embodiment of the present invention, a display apparatus with favorable display quality and performance can be provided. With one embodiment of the present invention, a high-resolution, high-emission-efficiency, and highly reliable display apparatus can be provided. With one embodiment of the present invention, a high-definition and highly reliable display apparatus with favorable display performance can be provided. With one embodiment of the present invention, a highly reliable display apparatus with favorable display quality and performance can be provided. A novel display apparatus, a novel display module, or a novel electronic device 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.
In general, a tandem light-emitting device includes, between electrodes, a plurality of light-emitting units each including a light-emitting layer, and an intermediate layer sandwiched between the light-emitting units. The intermediate layer 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. As the CGL, a layer in which a material having an acceptor property is mixed with a material having a carrier-transport property or a layer in which a material having a donor property is mixed with a material having a carrier-transport property is typically used. For example, as the CGL, a layer including a material having a hole-transport property and a material having an acceptor property or a layer including a material having an electron-transport property and a material having a donor property is used.
Using a stack of a layer including a material having a hole-transport property and a material having an acceptor property (CGL1) and a layer including a material having an electron-transport property and a material having a donor property (CGL2) as the CGL is preferable to facilitate injection of holes and electrons to the light-emitting units and thus reduce driving voltage. The CGL1 is formed on the cathode side, and the CGL2 is formed on the anode side. This is because injecting holes generated in the CGL1 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 CGL1 and injecting electrons generated in the CGL2 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 CGL2 can lower a carrier injection barrier. The CGL2 may be a single film of a material having a donor property. In that case, charge separation occurs between the material having a donor property and the electron-transport material in the light-emitting unit on the anode side; therefore, electrons can be regarded as being injected to the light-emitting unit at the time of charge separation. A tunnel current can flow between the CGL1 and the CGL2, or the CGL1 and the CGL2 can be combined to cause carrier recombination.
As a method for forming an organic semiconductor film in a predetermined shape, 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. An organic semiconductor device having a finer pattern is expected to be achieved by shape processing of an organic semiconductor film by a photolithography technique. Moreover, since a photolithography technique achieves large-area processing more easily than mask vapor deposition, processing of an organic semiconductor film by the photolithography technique is being researched.
It has been known that when EL layers in a light-emitting device mainly using an organic compound are exposed to atmospheric components such as water and oxygen, initial characteristics or reliability is affected, and thus it has been common knowledge that the EL layers are treated in a near-vacuum atmosphere.
In particular, an electron-injection layer in a light-emitting device or an intermediate layer used in a tandem light-emitting device, which often includes an alkali metal, an alkaline earth metal, or a compound thereof (hereinafter also referred to as a Li compound or the like) highly reactive with water or oxygen, rapidly deteriorates and loses the function as the electron-injection layer or the carrier-generation layer when the surface of the EL layer is exposed to the atmosphere as well as when the electron-injection layer or the carrier-generation layer is directly exposed to the atmosphere.
However, processing steps with the aforementioned photolithography technique inevitably expose the surface of the EL layer to the atmosphere and significantly lower the electron-injection property of the electron-injection layer or the intermediate layer including a Li compound or the like. The electron-transport layer can be formed after such processing. However, the intermediate layer is subjected to the processing; therefore, it has been difficult to perform processing by a photolithography technique for the tandem light-emitting device that uses the intermediate layer including a Li compound or the like.
Here, the present inventors have confirmed that a light-emitting device that uses an organic compound having strong basicity such as 1-(9,9′-spirobi[9H-fluoren]-2-yl)-1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine (abbreviation: 2hppSF), instead of a Li compound or the like, in its intermediate layer operates normally as a tandem light-emitting device in a certain structure.
The organic compound having strong basicity is less likely to deteriorate when being exposed to the atmosphere unlike the alkali metal, the alkaline earth metal, or the compound thereof. Thus, even when the organic compound having strong basicity is used in a light-emitting device formed through a processing step by a photolithography technique involving exposure to the atmosphere, deterioration of the light-emitting device due to the deterioration of the organic compound having strong basicity itself is unlikely to occur.
However, a tandem light-emitting device which is formed including the organic compound having strong basicity in its intermediate layer through a vacuum multi-chamber process has higher drive voltage than a device which is formed including an alkali metal, an alkaline earth metal, or a compound thereof in its intermediate layer through a vacuum multi-chamber process.
From these facts and additional experiments, the present inventors have found that a novel tandem light-emitting device including an organic compound having strong basicity in its intermediate layer with tolerance to processing in the atmosphere, high reliability, and low drive voltage can be manufactured when an electron-transport layer included in the light-emitting unit on the anode side has a bipolar property.
A mechanism of the tandem light-emitting device including the organic compound having strong basicity in the intermediate layer and the light-emitting device of one embodiment of the present invention are described below.
When using the organic compound having strong basicity instead of an alkali metal, an alkaline earth metal, or a compound thereof typified by a Li compound, since the organic compound having strong basicity does not function as a donor, charge separation does not occur in the layer including the organic compound having strong basicity. Accordingly, electrons supplied to the light-emitting unit on the anode side are not generated (the layer including the organic compound having strong basicity which does not cause carrier generation and thus is not a CGL is referred to as a donor-less layer (DLL)).
As illustrated in
In the tandem light-emitting device that uses the organic compound having strong basicity instead of the Li compound in the CGL2 in the above-described manner, the DLL does not function as a carrier-generation layer and thus the increase in drive voltage is significant even when the light-emitting device operates as a tandem light-emitting device.
The present inventors have discovered that the tandem light-emitting device that uses the organic compound having strong basicity instead of the Li compound in the CGL2 can operate as a tandem light-emitting device without a significant increase of drive voltage by making an electron-transport layer (hereinafter also referred to as a first electron-transport layer) in the light-emitting unit on the anode side (hereinafter also referred to as a first light-emitting unit) have a bipolar property.
This can be explained by new findings that the organic compound layer including the organic compound having strong basicity (DLL) makes electrons flow but blocks holes (does not make holes flow) and the driving mechanism of the tandem light-emitting device that is generation of electric dipole due to accumulation of electrical charges and the accompanying shift of the vacuum level.
In the tandem light-emitting device that uses the DLL including the organic compound having strong basicity instead of the CGL2, application of voltage in the above-described manner does not make the DLL generate electrons because the DLL does not function as a CGL. Holes injected to the first light-emitting unit from the anode are immediately accumulated in the interface on the first electron-transport layer side in the DLL as indicated by 400 in
Although electrons are induced from the CGL1 by the application of voltage and the hole accumulation at the interface on the first electron-transport layer side in the DLL, the electrons induced in the CGL1 are accumulated in the interface on the DLL side in the CGL1 (401 in
Consequently, the vacuum level shifts (403 in
From emission efficiency and reliability perspectives, a flow of holes that have passed through a light-emitting layer in an electron-transport layer is usually an unwelcome phenomenon. Therefore, a material having a low hole-transport property is selected as a material of the electron-transport layer, and a hole-block layer is often further provided in contact with a light-emitting layer between the light-emitting layer and the electron-transport layer. However, the light-emitting device of one embodiment of the present invention rather makes the electron-transport layer have a bipolar property, which enables a tandem light-emitting device with favorable characteristics.
In a light-emitting device having a normal structure with the first electron-transport layer not having a bipolar property (the first electron-transport layer blocking holes or not transporting holes), holes are accumulated in the interface on the first electron-transport layer side in the first light-emitting layer and the positions of the accumulated holes and electrons are distant from each other. Assuming that the same amount of carriers are accumulated, the light-emitting device having the normal structure has a weaker electric field due to electric dipole and thus has higher drive voltage.
The first electron-transport layer preferably has a bipolar property as described above, that is, is preferably an electron-transport layer having a relatively high hole-transport property. Accordingly, the highest occupied molecular orbital (HOMO) level of the organic compound included in the first electron-transport layer is preferably greater than or equal to −5.90 eV and less than or equal to −5.00 eV, further preferably greater than or equal to −5.80 eV and less than or equal to −5.00 eV, still further preferably greater than or equal to −5.70 eV and less than or equal to −5.15 eV. Since the first electron-transport layer also needs to have a high electron-transport property, the LUMO level of the organic compound included in the first electron-transport layer is preferably greater than or equal to −3.15 eV and less than or equal to −2.50 eV, further preferably greater than or equal to −3.00 eV and less than or equal to −2.70 eV.
The first electron-transport layer may be a layer formed of a plurality of organic compounds. In the case where a plurality of organic compounds are included in the first electron-transport layer, the HOMO level of the organic compound having the highest HOMO level is preferably within the above-described range. In the case where a plurality of organic compounds are included in the first electron-transport layer, the LUMO level of the organic compound having the lowest LUMO level is preferably within the above-described range. In the case where the first electron-transport layer is formed of a plurality of organic compounds, at least one of the organic compounds is preferably an organic compound having an electron-transport property and at least one of the organic compounds is preferably an organic compound having a hole-transport property.
The organic compound having an electron-transport property and the organic compound having a hole-transport property are preferably a single organic compound. In other words, it is preferable that the first electron-transport layer include an organic compound having both an electron-transport property and a hole-transport property because of facilitating formation of a light-emitting device with favorable characteristics.
The organic compound having an electron-transport property or the organic compound having both an electron-transport property and a hole-transport property preferably includes a substance having an electron mobility higher than or equal to 1×10−7 cm2/Vs, 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. The organic compound having a hole-transport property or the organic compound having both an electron-transport property and a hole-transport property preferably includes a substance having a hole mobility higher than or equal to 1×10−7 cm2/Vs, 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.
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 preferably includes an organic compound having an electron-transport skeleton and an organic compound having a hole-transport skeleton. The organic compound having an electron-transport skeleton and the organic compound having a hole-transport skeleton are preferably a single organic compound. In other words, it is preferable that the first electron-transport layer include an organic compound having both an electron-transport skeleton and a hole-transport skeleton because of facilitating formation of a light-emitting device with favorable characteristics.
Note that the electron-transport skeleton is preferably a skeleton having a π-electron deficient heteroaromatic ring. As the skeleton having a π-electron deficient heteroaromatic ring, a skeleton having at least one of a polyazole skeleton, a pyridine skeleton, a diazine skeleton, and a triazine skeleton in the ring is preferably used, for example. Specifically, a pyrimidine skeleton, a pyrazine skeleton, a pyridazine skeleton, a pyridine skeleton, a triazine skeleton, a benzofuropyrimidine skeleton, a benzothienopyrimidine skeleton, a benzofuropyrazine skeleton, a benzothienopyrazine skeleton, or the like is preferable. Among them, a pyrimidine skeleton, a pyrazine skeleton, a triazine skeleton, or a benzofuropyrimidine skeleton is preferable.
Furthermore, the hole-transport skeleton is preferably a skeleton having a π-electron rich heteroaromatic ring. 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 preferably used, for example. Specifically, a carbazole skeleton, a dibenzothiophene skeleton, or a skeleton in which an aromatic ring or a heteroaromatic ring is further condensed to a carbazole skeleton or a dibenzothiophene skeleton is preferable. Among them, a carbazole skeleton, a biscarbazole skeleton, or an indolocarbazole skeleton is preferable. An amine skeleton, especially a triphenylamine skeleton is also preferable.
As the organic compound included in the first electron-transport layer, an organic compound having both an electron-transport skeleton and a hole-transport skeleton is preferable. Specific examples of the organic compound include 3,6-bis(diphenylamino)-9-[4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl]-9H-carbazole (abbreviation: DACT-II), 2-{3-[3-(N-phenyl-9H-carbazol-3-yl)-9H-carbazol-9-yl]phenyl}dibenzo[f,h]quinoxaline (abbreviation: 2mPCCzPDBq), 9-[3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl]-9′-phenyl-2,3′-bi-9H-carbazole (abbreviation: mPCCzPTzn-02), and 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).
The organic compound included in the first electron-transport layer preferably exhibits thermally activated delayed fluorescence (TADF) (a TADF property). The organic compound having a TADF property has a high HOMO level, a low LUMO level, and short singlet and triplet excitation lifetimes; thus, in the case where recombination occurs in the first electron-transport layer, the excited state can be readily deactivated, providing a light-emitting device with high reliability. Among the preferable organic compounds included in the first electron-transport layer, DACT-II is the organic compound having a TADF property.
Examples of the organic compound having an electron-transport property in the case where the first electron-transport layer is formed of a plurality of kinds of organic compounds 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: 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), 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-(4-dibenzothienyl)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(BN2)-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-(1,l′-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-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), 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 drive voltage.
Examples of the organic compound having a hole-transport property in the case where the first electron-transport layer is formed of a plurality of kinds of organic compounds 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: BBαNβNB), 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: YGTBilBP), 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: YGTBiβNB), N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-N-[4-(1-naphthyl)phenyl]-9,9′-spirobi[9H-fluoren]-2-amine (abbreviation: PCβNBSF), 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: PCBBilBP), 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, N,N-bis(9,9-dimethyl-9H-fluoren-2-yl)-9,9′-spirobi-9H-fluoren-1-amine, 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).
Although the thickness of the first electron-transport layer is preferably small, a thickness of 5 nm to 10 nm is preferable in order to form a light-emitting device with high reliability.
The DLL accumulates holes injected from the anode and thus is a layer having a function of blocking holes or a layer that does not transport holes. The DLL needs to transport and inject, to the first light-emitting unit, electrons injected from the CGL1 and thus is a layer having an electron-transport property.
Whether the DLL blocks holes can be judged by forming an electronic device that makes only holes flow (hereinafter referred to as a hole-only device) and measuring the relation between current density and voltage. For example, in the case where the current density of a hole-only device shown in Table 1, in which a target layer is sandwiched, is extremely low, specifically in the case where the current density at 10 V of the measurement device shown in Table 1, in which the target layer is sandwiched, is lower than or equal to 0.01 mA/cm2, the target layer can be regarded as a layer that blocks holes.
In the table, ITSO represents indium tin oxide containing silicon oxide, PCBBIF represents N-(biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H-fluoren-2-amine, and OCHD-003 represents a fluorine-containing electron-acceptor material having a molecular weight of 672.
The relation between current density and voltage is compared between such a measurement device in which the layer 3 is not formed and the measurement device with the 10-nm-thick target layer as the layer 3. In the case where measurement is performed with the 10-nm-thick target layer serving as the layer 3 sandwiched, the target layer offering a current density at 10 V of lower than or equal to 0.01 mA/cm2 can be regarded as a layer that blocks holes.
From the graph, the layers formed of PCBBIF, βNCCP, mPPhen2P, mPPhen2P: PCBBiF (1:1 by weight), and mPPhen2ββNCCP (1:1 by weight) are layers that do not block holes, and the layers formed of mPPhen2P:2′,7′tBu-2hppSF (1: 1 by weight) and 2′, 7′tBu-2hppSF are layers that block holes.
In the case where the measurement target layer is a mixed layer of Material A and Material B, the hole-only device in which the mixed layer is provided as the measurement target layer (Device X) and the hole-only device in which a single layer of Material A or Material B, whichever has a deeper HOMO level, is provided as the measurement target layer (Device Y) are fabricated. In the case where the voltage at 1 mA/cm2 of Device X is higher than that of Device Y by 1 V or more, the mixed layer can be regarded as a layer that blocks holes.
The DLL preferably includes an organic compound having strong basicity with an acid dissociation constant pKa of 8 or more. By including the organic compound having strong basicity with a pKa of 8 or more, the DLL can block holes and accumulate holes at the interface on the first electron-transport layer side. It is preferable that the substance having strong basicity with an acid dissociation constant pKa of 8 or more, preferably 10 or more, further preferably 12 or more do not have an electron-transport skeleton in order to lower the probability of recombination with electrons in the DLL. Note that 2hppSF is a substance having strong basicity with an acid dissociation constant pKa of 13.95, and 2′,7′tBu-2hppSF is a substance having strong basicity with an acid dissociation constant pKa of 14.18.
A material with a large acid dissociation constant pKa blocks holes because the material with a large acid dissociation constant pKa has a large dipole moment. The dipole moment mutually interacts with holes, whereby the DLL including the material with a large acid dissociation constant pKa can block holes.
Another reason for hole blocking is high nucleophilicity of the material with a large acid dissociation constant pKa. A material with high nucleophilicity reacts with a molecule that has become a cation radical by receiving a hole to generate a new molecule or intermediate state, in some cases. This reaction consumes holes and can significantly reduce the hole-transport property in the DLL.
It is preferable that the above-described substance having strong basicity with a pKa of 8 or more do not have an electron-transport skeleton in order to inhibit recombination of electrons injected to the DLL and holes trapped by the material with a large acid dissociation constant pKa and efficiently inject electrons to the first light-emitting unit.
Note that the substance with an acid dissociation constant pKa of 8 or more is preferably an organic compound having a basic skeleton and an acid dissociation constant pKa of the basic skeleton of 10 or more. In the organic compound, the acid dissociation constant pKa of the basic skeleton is further preferably 12 or more.
As the acid dissociation constant pKa of the basic skeleton, the acid dissociation constant value of the organic compound formed by substituting hydrogen for part of the skeleton can be used. As an indicator of acidity of an organic compound having a basic skeleton, the acid dissociation constant pKa of the basic skeleton can be used. As for an organic compound having a plurality of basic skeletons, the acid dissociation constant pKa of the basic skeleton having the highest acid dissociation constant pKa can be used as the indicator of acidity of the organic compound. The acid dissociation constant pKa is preferably a value measured using water as a solvent.
Alternatively, the acid dissociation constant pKa of the organic compound may be calculated as follows.
First, as the initial molecular structure in each molecule that is a calculation model, the most stable structure (singlet ground state) obtained from the first-principles calculation is used.
For the first-principles calculation, Jaguar, which is the quantum chemical computational software produced by Schrodinger, Inc., was used, and the most stable structure in the singlet ground state was calculated by the density functional theory (DFT). As a basis function, 6-31G ** was used, and as a functional, B3LYP-D3 was used. The structure subjected to quantum chemical calculation is sampled by conformational analysis in mixed torsional/low-mode sampling with Maestro GUI produced by Schrodinger, 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). For the molecule with one or more atoms designated as basic sites, the largest pKa value among the obtained results is employed.
The organic compound with a large acid dissociation constant pKa is preferably an organic compound having a pyrrolidine skeleton, a piperidine skeleton, or a hexahydropyrimidopyrimidine skeleton. Alternatively, an organic compound having a guanidine skeleton is preferably used. As specific examples, organic compounds having any of basic skeletons represented by Structural Formulae (120) to (123) below can be given.
It is preferable that the organic compound with an acid dissociation constant pKa of 8 or more be specifically an organic compound which has a bicyclo ring structure having 2 or more nitrogen atoms in the bicyclo ring and a heteroaromatic hydrocarbon ring having 2 to 30 carbon atoms in the ring or an aromatic hydrocarbon ring having 6 to 30 carbon atoms in the ring, and more specifically be an organic compound which has a 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine skeleton and a heteroaromatic hydrocarbon ring having 2 to 30 carbon atoms in the ring or an aromatic hydrocarbon ring having 6 to 30 carbon atoms in the ring. An organic compound which has a bicyclo ring structure having 2 or more nitrogen atoms in the bicyclo ring and a heteroaromatic hydrocarbon ring having 2 to 30 carbon atoms in the ring, more specifically an organic compound which has a 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine skeleton and a heteroaromatic hydrocarbon ring having 2 to 30 carbon atoms in the ring is further preferred.
Further specifically, the organic compound with an acid dissociation constant pKa of 8 or more is preferably an organic compound represented by General Formula (G1) below.
In the organic compound represented by General Formula (G1) above, X represents a group represented by General Formula (G1-1) below, and Y represents a group represented by General Formula (G1-2) below. R1 and R2 each independently represent hydrogen or deuterium, h represents an integer of 1 to 6, and Ar represents a substituted or unsubstituted heteroaromatic hydrocarbon ring having 2 to 30 carbon atoms in the ring or a substituted or unsubstituted aromatic hydrocarbon ring having 6 to 30 carbon atoms in the ring. Ar is preferably the substituted or unsubstituted heteroaromatic hydrocarbon ring having 2 to 30 carbon atoms in the ring.
In General Formulae (G1-1) and (G1-2) above, R3 to R6 each independently represent hydrogen or deuterium, m represents an integer of 0 to 4, n represents an integer of 1 to 5, and m+1> n (m+1 is larger than or equal to n) is satisfied. Note that in the case where m or n is 2 or more, R3s may be the same or different, and the same applies to R4s, R5s, and R6s.
The organic compound represented by General Formula (G1) above is preferably any one of compounds represented by General Formulae (G2-1) to (G2-6) below.
R11 to R26 each independently represent hydrogen or deuterium, h represents an integer of 1 to 6, and Ar represents a substituted or unsubstituted heteroaromatic hydrocarbon ring having 2 to 30 carbon atoms in the ring or a substituted or unsubstituted aromatic hydrocarbon ring having 6 to 30 carbon atoms in the ring. Ar is preferably the substituted or unsubstituted heteroaromatic hydrocarbon ring having 2 to 30 carbon atoms in the ring.
In General Formula (G1) and General Formulae (G2-1) to (G2-6) above, the substituted or unsubstituted heteroaromatic hydrocarbon ring having 2 to 30 carbon atoms in the ring or the substituted or unsubstituted aromatic hydrocarbon ring having 6 to 30 carbon atoms in the ring that is represented by Ar is specifically a pyridine ring, a bipyridine ring, a pyrimidine ring, a bipyrimidine ring, a pyrazine ring, a bipyrazine ring, a triazine ring, a quinoline ring, an isoquinoline ring, a benzoquinoline ring, a phenanthroline ring, a quinoxaline ring, a benzoquinoxaline ring, a dibenzoquinoxaline ring, an azofluorene ring, a diazofluorene ring, a carbazole ring, a benzocarbazole ring, a dibenzocarbazole ring, a dibenzofuran ring, a benzonaphthofuran ring, a dinaphthofuran ring, a dibenzothiophene ring, a benzonaphthothiophene ring, a dinaphthothiophene ring, a benzofuropyridine ring, a benzofuropyrimidine ring, a benzothiopyridine ring, a benzothiopyrimidine ring, a naphthofuropyridine ring, a naphthofuropyrimidine ring, a naphthothiopyridine ring, a naphthothiopyrimidine ring, an acridine ring, a xanthene ring, a phenothiazine ring, a phenoxazine ring, a phenazine ring, a triazole ring, an oxazole ring, an oxadiazole ring, a thiazole ring, a thiadiazole ring, an imidazole ring, a benzimidazole ring, a pyrazole ring, a pyrrole ring, or the like. In General Formula (G1) and General Formulae (G2-1) to (G2-6) above, the substituted or unsubstituted heteroaromatic hydrocarbon ring having 6 to 30 carbon atoms in the ring that is represented by Ar is specifically a benzene ring, a naphthalene ring, a fluorene ring, a dimethylfluorene ring, a diphenylfluorene ring, a spirofluorene ring, an anthracene ring, a phenanthrene ring, a triphenylene ring, a pyrene ring, a tetracene ring, a chrysene ring, a benzo[a]anthracene ring, or the like. Ar is especially preferably represented by any one of Structural Formulae (Ar-1) to (Ar-27) below.
Note that Ar preferably has a nitrogen atom in its ring and is preferably bonded to the skeleton within parentheses in General Formula (G1) above by a bond of the nitrogen atom or a carbon atom adjacent to the nitrogen atom.
As specific examples of the organometallic compounds represented by General Formula (G1) and General Formulae (G2-1) to (G2-6) above, organic compounds represented by Structural Formulae (101) to (117) below, such as 1,1′-(9,9′-spirobi[9H-fluorene]-2,7-diyl)bis(1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine) (abbreviation: 2,7hpp2SF) (Structural Formula 108), 1-(9,9′-spirobi[9H-fluoren]-2-yl)-1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine (abbreviation: 2hppSF) (Structural Formula 109), and 1-(2 ′,7′-di-tert-butyl-9,9′-spirobi[9H-fluoren]-2-yl)-1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine (abbreviation: 2′,7′tBu-2hppSF), can be given.
Unlike an alkali metal, an alkaline earth metal, or a compound thereof, these organic compounds do not have a concern about metal contamination in a production line and can be easily evaporated as well as being stable, for example, and thus can be favorably used in light-emitting devices formed through a photolithography process. Needless to say, it is also effective to use these organic compounds for light-emitting devices formed not through a photolithography process.
Note that it is preferable that the substance having strong basicity with a pKa of 8 or more do not have an electron-transport skeleton from the viewpoint of inhibiting recombination of the injected electrons and blocked holes in the substance having strong basicity with a pKa of 8 or more. As the substance having strong basicity with a pKa of 8 or more, an organic compound such as 1-(9,9′-spirobi[9H-fluoren]-2-yl)-1,3,4,6, 7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine (abbreviation: 2hppSF), 1-(2 ′,7′-di-tert-butyl-9,9′-spirobi[9H-fluoren]-2-yl)-1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine (abbreviation: 2 ′, 7′tBu-2hppSF), 2,9-bis(1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidin-1-yl)-1,10-phenanthroline (abbreviation: 2,9hpp2Phen), 4,7-di-1-pyrrolidinyl-1,10-phenanthroline (abbreviation: Pyrrd-Phen), or 8,8′-pyridin-2,6-diyl-bis(5,6,7,8-tetrahydroimidazo[1,2-a]pyrimidine) (abbreviation: 2,6tip2Py) can specifically be used.
Furthermore, the DLL preferably includes a material having an electron-transport property in addition to the substance having strong basicity with a pKa of 8 or more. 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 a polyazole 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 drive voltage. A benzofuropyrimidine skeleton, a benzothienopyrimidine skeleton, a benzofuropyrazine skeleton, and a benzothienopyrazine skeleton are preferable because of their high reliability.
As the organic compound having a π-electron deficient heteroaromatic ring skeleton, any of the materials given as examples of the organic compound having an electron-transport property in the first electron-transport layer can be used. 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 drive voltage. An organic compound having a phenanthroline skeleton 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. Furthermore, a material having a pyridine skeleton or a phenanthroline skeleton, which has a large pKa and thus has a high hole-blocking property, is particularly preferable as an electron-transport material used in the DLL of a light-emitting device of one embodiment of the present invention.
The LUMO level of the material having an electron-transport property in the DLL is preferably greater than or equal to −3.00 eV and less than or equal to −2.00 eV in order to lower a barrier to electron injection to the light-emitting layer.
The thickness of the DLL is preferably small; however, too large a thickness increases drive voltage and too small a thickness worsens characteristics, particularly reliability. Therefore, the thickness of the DLL is preferably greater than or equal to 2 nm and less than or equal to 13 nm, further preferably greater than or equal to 5 nm and less than or equal to 10 nm.
Moreover, it is preferable that the substance having strong basicity in the DLL do not have an electron-donating property. Furthermore, it is preferable that the substance having strong basicity do not have a property of donating electrons to the material having an electron-transport property. In the case where the substance having strong basicity has an electron-donating property, the substance easily reacts with atmospheric components such as water and oxygen and is poor in stability. Because the DLL can have a significantly lowered hole-transport property by including the substance having strong basicity and the material having an electron-transport property, the DLL can function as an intermediate layer of the tandem light-emitting device even when the substance having strong basicity does not have an electron-donating property. Accordingly, the intermediate layer and the tandem light-emitting device that are stable with respect to atmospheric components such as water and oxygen can be formed. It is preferable that a signal observed by electron spin resonance (ESR) spectroscopy on the DLL be small or no signal be observed. For example, the spin density attributed to a signal observed at a g-factor of approximately 2.00 is preferably lower than or equal to 1×1017 spins/cm3, further preferably lower than 1×1016 spins/cm3.
The CGL1 is preferably formed using a composite material containing a material having an electron-acceptor property and an organic compound having a hole-transport property.
The material having an electron-acceptor property in the CGL1 preferably has a property of accepting electrons. The material having an electron-acceptor property preferably has an electron-accepting property with respect to an organic compound having a hole-transport property. The CGL1 can function as a carrier-generation layer by including the material having an electron-acceptor property owing to charge separation in the CGL1 and thus can function as an intermediate layer of a tandem light-emitting device. Furthermore, it is preferable that a signal be observed by electron spin resonance spectroscopy on the CGL1. For example, the spin density 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.
Examples of the substance having an 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-dicyanomethylene-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-accepting 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 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.
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 T-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; l′-binaphthyl-2-yl)triphenylamine (abbreviation: BBAαNβNB), 4,4′-diphenyl-4″-(7;l′-binaphthyl-2-yl)triphenylamine (abbreviation: BBANβNB-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: «NBB1BP), 4,4′-diphenyl-4″-[4′-(carbazol-9-yl)biphenyl-4-yl]triphenylamine (abbreviation: YGTBilBP), 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: YGTBiβNB), N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-N-[4-(1-naphthyl)phenyl]-9,9′-spirobi[9H-fluoren]-2-amine (abbreviation: PCβNBSF), 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: PCBBilBP), 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).
An electron-relay layer is preferably provided between the CGL1 and the DLL. The electron-relay layer has at least an electron-transport property and has a function of preventing interaction between the CGL1 and the DLL and smoothly transferring electrons. The LUMO level of the substance having an electron-transport property included in the electron-relay layer is preferably positioned between the LUMO level of the acceptor substance in the CGL1 and the LUMO level of the substance having an electron-transport property included in the DLL. Specifically, the LUMO level of the substance having an electron-transport property included in the electron-relay layer is higher than or equal to −5.00 eV, preferably higher than or equal to −5.00 eV and lower than or equal to −3.00 eV, further preferably higher than or equal to −5.00 eV and lower than or equal to −3.25 eV. Note that as the substance having an electron-transport property included in the electron-relay layer, a phthalocyanine-based material or a metal complex having a metal-oxygen bond and an aromatic ligand is preferably used.
The light-emitting device of one embodiment of the present invention having the above-described structure can have high current efficiency and a suppressed increase in drive 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.
In this embodiment, a light-emitting device 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 a first electron-transport layer 114_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 and a first hole-transport layer 112_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 layer 119 (the DLL in Embodiment 1) and a second layer 117 (the CGL1 in Embodiment 1) from the anode (the first electrode 101 in
Since the structures of the first layer 119, the second layer 117, and the third layer 118 have been specifically described in detail as the structures of the DLL, the CGL1, and the electron-relay layer 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 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-dicyanomethylene-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-accepting 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 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 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; l′-binaphthyl-2-yl)triphenylamine (abbreviation: BBANβNB), 4,4′-diphenyl-4″-(7; l′-binaphthyl-2-yl)triphenylamine (abbreviation: BBANβNB-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: YGTBilBP), 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: YGTBiβNB), N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-N-[4-(1-naphthyl)phenyl]-9,9′-spirobi[9H-fluoren]-2-amine (abbreviation: PCβNBSF), 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 acceptor property, the organic compound having an 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: βNCCP), 9-(3-biphenyl)-9′-(2-naphthyl)-3,3′-bi-9H-carbazole (abbreviation: BNCCmBP), 9-(4-biphenyl)-9′-(2-naphthyl)-3,3′-bi-9H-carbazole (abbreviation: BNCCBP), 9,9′-di-2-naphthyl-3,3′-9H,9′H-bicarbazole (abbreviation: BisβNCz), 9-(2-naphthyl)-9′-[1,l′: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,l′: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′-9-(triphenylen-2-yl)-9′-[1,1′:3′, 1″-terphenyl]-4-yl-3,3′-9H,9′H- 9H,9′H-bicarbazole, 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-5,9-dihydro-5,9-diaza-13b-boranaphtho[3,2, 1-de]anthracene-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-kI]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-kI]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-kI]phenazaborine (abbreviation: Me-tBu4DABNA), N7,N7,N13,N13,5,9,11,15-octaphenyl-5H,9H,11H,15H-[1,4]benzazaborino[2,3,4-kI][1,4]benzazaborino[4′,3′,2′:4,5][1,4]benzazaborino[3,2-b]phenazaborin-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-kI]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-kI]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-flphenanthridinato]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: FIr(acac)). 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: tris(4-1-butyl-6-phenylpyrimidinato)iridium(III) (abbreviation: [Ir(mppm)3]), [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: [Ir(ppy)3]), bis(2-phenylpyridinato-N,C2′)iridium(III) acetylacetonate (abbreviation: [Ir(ppy)2(acac)]), bis(benzo[h]quinolinato)iridium(III) acetylacetonate (abbreviation: [Ir(bzq)2(acac)]), tris(benzo[h]quinolinato)iridium(III) (abbreviation: [Ir(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-K(]bis[2-(2-pyridinyl-κN)phenyl-κC]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(dlnpm)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-K( ),K( ))bis[2,4-dimethyl-6-[7-(1-methylethyl)-1-isoquinolinyl-κN]phenyl-K(]iridium(III), and (3,7-diethyl-4,6-nonanedionato-K( ),K( ))bis[2,4-dimethyl-6-[5-(1-methylethyl)-2-quinolinyl-κN]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-a]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 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-donating property of the π-electron rich heteroaromatic ring and the electron-accepting 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 T-electron rich skeleton, an aromatic amine skeleton, a phenazine skeleton, or the like can be used. As a T-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 5 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 x-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 a polyazole 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 drive voltage. A benzofuropyrimidine skeleton, a benzothienopyrimidine skeleton, a benzofuropyrazine skeleton, and a benzothienopyrazine skeleton are preferable because of their high 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: 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), 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: m TpPPhen), 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-(4-dibenzothienyl)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(BN2)-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-(1,1′-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-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), 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 drive 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 addition, 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 which brings about light emission) of the fluorescent substance. As the protective group, a substituent having no x 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 x 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 x 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: αN-BNPAnth), 9-(1-naphthyl)-10−(2-naphthyl)anthracene (abbreviation: α,BADN), 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: BN-mBNPAnth), 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 may be 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.
Since the structure of the first electron-transport layer 114_1 has been described in detail in Embodiment 1, the repetitive description thereof is omitted. The second electron-transport layer 114_2 contains 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 a polyazole 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 compound having an electron-transport property that can be used in 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 drive voltage. An organic compound having a phenanthroline skeleton 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 114_1 and the second electron-transport layer 114_2 may have a stacked-layer structure. In the case where the first electron-transport layer 114_1 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 114_2 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 electride 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 electride 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
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 by 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 by 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.
Described in this embodiment is a mode in which the light-emitting 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, an 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 (yellow), 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 light-emitting device 130 is provided over the insulating layer 175 and the plug 176. A protective layer 131 is provided to cover the light-emitting 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 light-emitting 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 light-emitting devices are formed. Note that the display apparatus of one embodiment of the present invention may be of a bottom emission type.
The light-emitting device 130R has a structure as described in Embodiments 1 and 2. The light-emitting 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. Furthermore, a plurality of layers such as an electron-injection layer may be provided as common layers in contact with the second electrode 102 (common electrode).
The light-emitting device 130G has a structure as described in Embodiments 1 and 2. The light-emitting 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 light-emitting device 130B has a structure as described in Embodiments 1 and 2. The light-emitting 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 light-emitting 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 light-emitting devices 130 can suppress leakage current between the adjacent light-emitting 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 is formed by forming an EL film and processing the EL film by a photolithography technique.
The first EL layer 104 is preferably provided to cover the top surface and the side surface of the first electrode 101 (pixel electrode) of the light-emitting device 130. In this case, the aperture ratio of the display apparatus can be easily increased as compared to the structure where an end portion of the first EL layer 104 is positioned inward from an end portion of the pixel electrode. Covering the side surface of the pixel electrode of the light-emitting device 130 with the first EL layer 104 can inhibit the pixel electrode from being in contact with the second electrode 102; hence, a short circuit of the light-emitting device 130 can be inhibited.
In the display apparatus of one embodiment of the present invention, the first electrode 101 (pixel electrode) of the light-emitting 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 of 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 light-emitting 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 reliability.
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
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 light-emitting 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
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, part of the sacrificial film 158Gf is removed using the mask layer 159G as a mask, so that the sacrificial layer 158G is formed. Next, the organic compound film 103Gf is processed to form the organic compound layer 103G. Accordingly, as illustrated in FIG. 7B, the stacked-layer structure of the organic compound layer 103G, the sacrificial layer 158G, and the mask layer 159G remains over the conductive layer 152G. The mask layer 159R and the conductive layer 152B are exposed.
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 60° 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 light-emitting 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 light-emitting 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 layers. 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 ºC, 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 Cl2, 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 light-emitting 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 over 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 first EL layers 104R, 104G, and 104B 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 light-emitting devices formed by a photolithography technique can have favorable characteristics.
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 light-emitting devices 130R, 130G, and 130B are provided over the insulating layer 175. An insulator is provided in regions between adjacent light-emitting 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 light-emitting 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 light-emitting 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 a light-emitting 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
Embodiment 1 to Embodiment 3 can be referred to for the details of the light-emitting devices 130R, 130G, and 130B.
The light-emitting 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 light-emitting 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 light-emitting 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 light-emitting 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 light-emitting device 130R; the same applies to the conductive layers 224B, 151B, and 152B and the insulating layer 156B in the light-emitting 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 light-emitting 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 light-emitting device 130. In
The display apparatus 100B has a top-emission structure. Light from the light-emitting 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 light-emitting 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 572 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. A 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 light-emitting 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 in
Light from the light-emitting 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 light-emitting 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 light-emitting 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 light-emitting 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 light-emitting 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 embodiments 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 apparatus, 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 1-1 and a light-emitting device 1-2 of embodiments of the present invention and a comparative light-emitting device 1-3, 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 10 nm-thick indium tin oxide containing silicon oxide (ITSO) were stacked sequentially from the substrate side by a sputtering method as a reflective electrode and a transparent electrode, respectively, over a glass substrate, 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, baking was performed at 200° C. for one hour, and then UV ozone treatment was performed for 370 seconds.
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 substrate 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 a fluorine-containing electron acceptor material with 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 20 nm, whereby a first hole-transport layer was formed.
Then, over the first hole-transport layer, 4,8-bis[3-(dibenzothiophen-4-yl)phenyl]-[1]benzofuro[3,2-d]pyrimidine (abbreviation: 4,8mDBtP2Bfpm) represented by Structural Formula (ii) above, 9-(2-naphthyl)-9′-phenyl-9H,9′H-3,3′-bicarbazole (abbreviation: βNCCP) represented by Structural Formula (iii) above, and [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)) represented by Structural Formula (iv) above were deposited by co-evaporation to a thickness of 40 nm such that the weight ratio of 4,8mDBtP2Bfpm to βNCCP and Ir(ppy)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 25 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 (vi) above and 1-(9,9′-spirobi[9H-fluoren]-2-yl)-1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine (abbreviation: 2hppSF) 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 2hppSF was 1:1, copper phthalocyanine (abbreviation: CuPc) represented by Structural Formula (viii) above was deposited by evaporation to a thickness of 2 nm, and 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, whereby an intermediate layer was formed.
Over the intermediate layer, PCBBiF was deposited by evaporation to a thickness of 40 nm, whereby a second hole-transport layer was formed.
Over the second hole-transport layer, 4,8mDBtP2Bfpm, βNCCP, and Ir(ppy)2(mbfpypy-d3) were deposited by co-evaporation to a thickness of 40 nm such that the weight ratio of 4,8mDBtP2Bfpm to βNCCP and Ir(ppy)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.
Over the second electron-transport layer, 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 2:1, 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. In this manner, the light-emitting device of one embodiment of the present invention was fabricated. Over the second electrode 102, 4,4 ′,4″-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation: DBT3P-II) represented by Structural Formula (ix) 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 1-1 was fabricated.
The light-emitting device 1-2 was fabricated in a manner similar to that of the light-emitting device 1-1 except that the material of the first electron-transport layer in the light-emitting device 1-1 was replaced by 2-[4′-(9-phenyl-9H-carbazol-3-yl)-3,1′-biphenyl-1-yl]dibenzo[f,h]quinoxaline (abbreviation: 2mpPCBPDBq) represented by Structural Formula (x) above.
The light-emitting device 1-3 was fabricated in a manner similar to that of the light-emitting device 1-1 except that the material of the first electron-transport layer in the light-emitting device 1-1 was replaced by 2-[3-(3′-dibenzothiophen-4-yl)biphenyl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTBPDBq-II) represented by Structural Formula (xi) above.
Device structures of the light-emitting devices 1-1 to 1-3 and the HOMO and LUMO levels of the organic compounds used in the first light-emitting layers and the first electron-transport layers of the light-emitting devices are shown below.
Note that the HOMO level and the LUMO level were obtained through cyclic voltammetry (CV) measurement.
In the cyclic voltammetry (CV) measurement, the values (E) of HOMO and LUMO levels were calculated on the basis of an oxidation peak potential (Epa) and a reduction peak potential (Epc), which were obtained by changing the potential of a working electrode with respect to a reference electrode. In the measurement, the HOMO level and the LUMO level were obtained by potential scanning in positive direction and potential scanning in negative direction, respectively. The scanning speed in the measurement was 0.1 V/s.
Specifically, a standard oxidation-reduction potential (E) (=Epa+Epc)/2) was calculated from an oxidation peak potential (Epa) and a reduction peak potential (Epc), which were obtained by the cyclic voltammogram of a material. Then, the standard oxidation-reduction potential (Eo) was subtracted from the potential energy (Ex) of the reference electrode with respect to a vacuum level, whereby each of the values (E) (=Ex−Eo) of HOMO and LUMO levels were obtained.
Note that the reversible oxidation-reduction wave was obtained in the above case; in the case where an irreversible oxidation-reduction wave is obtained, the HOMO level is calculated as follows: a value obtained by subtracting a predetermined value (0.1 eV) from an oxidation peak potential (Epa) is assumed to be a reduction peak potential (Epc), and a standard oxidation-reduction potential (Eo) is calculated to one decimal place. To calculate the LUMO level, a value obtained by adding a predetermined value (0.1 eV) to a reduction peak potential (Epc) was assumed to be an oxidation peak potential (Epa), and a standard oxidation-reduction potential (Eo) was calculated to one decimal place.
As shown above, the organic compounds each having a HOMO level greater than or equal to −5.9 eV and less than or equal to −5.0 eV are used in the first electron-transport layers in the light-emitting devices 1-1 and 1-2. The first layer of mPPhen2P: 2hppSF=1:1 formed in the intermediate layer is a film blocking holes. Furthermore, 2hppSF has an acid dissociation constant pKa of 13.95 and is an organic compound having strong basicity with a pKa of 8 or more. In addition, mPPhen2P, which is an organic compound having an electron-transport property and a LUMO level greater than or equal to −3.0 eV and less than or equal to −2.0 eV, is used in the first layer.
Here, an electron spin resonance spectrum of a thin film of mPPhen2P and 2hppSF that was deposited by co-evaporation to a thickness of 50 nm over a quartz substrate such that the weight ratio of mPPhen2P to 2hppSF was 1:1 was measured at room temperature, revealing that a signal was hardly observed at g-factors of approximately 2.00 and the spin density was lower than 8×1016 spins/cm3, which is the detection limit. Note that the measurement of electron spin resonance spectrum using ESR spectroscopy 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. This means that 2hppSF does not exhibit an electron-donating property with respect to mPPhen2P.
The second layer is a layer including PCBBiF, which is an organic compound having a hole-transport property, and OCHD-003 exhibiting an electron-acceptor property and is a carrier-generation layer in which charge separation occurs by voltage application.
Here, an electron spin resonance spectrum of a thin film of PCBBiF and OCHD-003 that was 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 was measured at room temperature, revealing that a signal was observed at a g-factor of approximately 2.00 and the spin density was 5×1019 spins/cm3. Note that the measurement of electron spin resonance spectrum using ESR spectroscopy 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. This means that OCHD-003 exhibits an electron-accepting property with respect to PCBBiF and the layer including PCBBiF and OCHD-003 functions as a carrier-generation layer.
Furthermore,
Thus, the use of the structure of the present invention can provide a light-emitting device having high emission efficiency, low drive voltage, and favorable characteristics.
Described in this example are specific methods for fabricating a light-emitting device 2-1 to a light-emitting device 2-5 of embodiments of the present invention and a comparative light-emitting device 2-6, 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 10 nm-thick indium tin oxide containing silicon oxide (ITSO) were stacked sequentially from the substrate side by a sputtering method as a reflective electrode and a transparent electrode, respectively, over a glass substrate, 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, baking was performed at 200° C. for one hour, and then UV ozone treatment was performed for 370 seconds.
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 substrate 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 a fluorine-containing electron acceptor material with 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 20 nm, whereby a first hole-transport layer was formed.
Then, over the first hole-transport layer, 4,8-bis[3-(dibenzothiophen-4-yl)phenyl]-[1]benzofuro[3,2-d]pyrimidine (abbreviation: 4,8mDBtP2Bfpm) represented by Structural Formula (ii) above, 9-(2-naphthyl)-9′-phenyl-9H,9′H-3,3′-bicarbazole (abbreviation: βNCCP) represented by Structural Formula (iii) above, and [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)) represented by Structural Formula (iv) above were deposited by co-evaporation to a thickness of 40 nm such that the weight ratio of 4,8mDBtP2Bfpm to βNCCP and Ir(ppy)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 20 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 (vi) above and 1-(9,9′-spirobi[9H-fluoren]-2-yl)-1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine (abbreviation: 2hppSF) represented by Structural Formula (vii) above were deposited by co-evaporation to a thickness of 10 nm such that the weight ratio of mPPhen2P to 2hppSF was 1:1, copper phthalocyanine (abbreviation: CuPc) represented by Structural Formula (viii) above was deposited by evaporation to a thickness of 2 nm, and 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, whereby an intermediate layer was formed.
Over the intermediate layer, PCBBiF was deposited by evaporation to a thickness of 40 nm, whereby a second hole-transport layer was formed.
Over the second hole-transport layer, 4,8mDBtP2Bfpm, βNCCP, and Ir(ppy)2(mbfpypy-d3) were deposited by co-evaporation to a thickness of 40 nm such that the weight ratio of 4,8mDBtP2Bfpm to βNCCP and Ir(ppy)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.
Over the second electron-transport layer, 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 2:1, 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. In this manner, the light-emitting device of one embodiment of the present invention was fabricated. Over the second electrode 102, 4,4 ′,4″-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation: DBT3P-II) represented by Structural Formula (ix) 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 2-1 was fabricated.
The light-emitting device 2-2 was fabricated in a manner similar to that of the light-emitting device 2-1 except that the first electron-transport layer in the light-emitting device 2-1 was formed by depositing 2-[3-(3′-dibenzothiophen-4-yl)biphenyl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTBPDBq-II) represented by Structural Formula (xi) above and N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]bis(9,9-dimethyl-9H-fluoren-2-yl)amine (abbreviation: PCBFF) represented by Structural Formula (xii) above by co-evaporation to a thickness of 20 nm such that the weight ratio of 2mDBTBPDBq-II to PCBFF was 1:1.
The light-emitting device 2-3 was fabricated in a manner similar to that of the light-emitting device 2-1 except that the first electron-transport layer in the light-emitting device 2-1 was formed by depositing 2mDBTBPDBq-II and 4,4′-diphenyl-4″-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBBilBP) represented by Structural Formula (xiii) above by co-evaporation to a thickness of 20 nm such that the weight ratio of 2mDBTBPDBq-II to PCBBilBP was 1:1.
The light-emitting device 2-4 was fabricated in a manner similar to that of the light-emitting device 2-1 except that the first electron-transport layer in the light-emitting device 2-1 was formed by depositing 2mDBTBPDBq-II and 9,9′-diphenyl-9H,9′H-3,3′-bicarbazole (abbreviation: PCCP) represented by Structural Formula (xiv) above by co-evaporation to a thickness of 20 nm such that the weight ratio of 2mDBTBPDBq-II to PCCP was 1:1.
The light-emitting device 2-5 was fabricated in a manner similar to that of the light-emitting device 2-1 except that the first electron-transport layer in the light-emitting device 2-1 was formed by depositing 2mDBTBPDBq-II and 9-[4-(9-phenyl-9H-carbazol-3-yl)-phenyl]phenanthrene (abbreviation: PCPPn) represented by Structural Formula (xv) above by co-evaporation to a thickness of 20 nm such that the weight ratio of 2mDBTBPDBq-II to PcPPn was 1:1.
The light-emitting device 2-6 was fabricated in a manner similar to that of the light-emitting device 2-1 except that 2mPCCzPDBq in the first electron-transport layer in the light-emitting device 2-1 was replaced by 2mDBTBPDBq-II.
Device structures of the light-emitting devices 2-1 to 2-6 and the HOMO and LUMO levels of the main organic compounds used in the light-emitting devices are shown below. Note that the HOMO level and the LUMO level were obtained through cyclic voltammetry (CV) measurement in a manner similar to that of Example 1.
Thus, the light-emitting devices 2-1 and 2-6 each use a single material in the first electron-transport layer, while the light-emitting devices 2-2 to 2-5 each use two kinds of organic compounds in the first electron-transport layer.
In the light-emitting device 2-1, the organic compound used in the first electron-transport layer has a HOMO level greater than or equal to −5.9 eV and less than or equal to −5.0 eV. In the light-emitting devices 2-2 to 2-5, the organic compound that has a higher HOMO level out of the two organic compounds included in the first electron-transport layer has a HOMO level greater than or equal to −5.9 eV and less than or equal to −5.0 eV. In the light-emitting device 2-6, the HOMO level of the organic compound used in the first electron-transport layer is −6.22 eV, which is outside the −5.9 eV to −5.0 eV range.
Furthermore, 2hppSF is used in the first layer included in the intermediate layer. Since 2hppSF has an acid dissociation constant pKa of 13.95, an organic compound having strong basicity with a pKa of 8 or more is used in the intermediate layer in each of the light-emitting devices 2-1 to 2-6. In addition, mPPhen2P, which is an organic compound having an electron-transport property and a LUMO level greater than or equal to −3.0 eV and less than or equal to −2.0 eV, is used in the first layer. Although the layer with mPPhen2P:2hppSF=1:1 is formed as the first layer, this layer is a film blocking holes.
Here, an electron spin resonance spectrum of a thin film of mPPhen2P and 2hppSF that was deposited by co-evaporation to a thickness of 50 nm over a quartz substrate such that the weight ratio of mPPhen2P to 2hppSF was 1:1 was measured at room temperature, revealing that a signal was hardly observed at g-factors of approximately 2.00 and the spin density was lower than 8×1016 spins/cm3, which is the detection limit. Note that the measurement of electron spin resonance spectrum using ESR spectroscopy was performed with an electron spin resonance spectrometer E500 (manufactured by Bruker Corporation) in a manner similar to that of Example 1. This means that 2hppSF does not exhibit an electron-donating property with respect to mPPhen2P.
The second layer is a layer including PCBBIF, which is an organic compound having a hole-transport property, and OCHD-003 exhibiting an electron-acceptor property and is a carrier-generation layer in which charge separation occurs by voltage application.
Here, an electron spin resonance spectrum of a thin film of PCBBiF and OCHD-003 that was 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 was measured at room temperature, revealing that a signal was observed at a g-factor of approximately 2.00 and the spin density was 5×1019 spins/cm3. Note that the measurement of electron spin resonance spectrum using ESR spectroscopy was performed with an electron spin resonance spectrometer JES FA300 (manufactured by JEOL Ltd.) in a manner similar to that of Example 1. This means that OCHD-003 exhibits an electron-accepting property with respect to PCBBiF and the layer including PCBBiF and OCHD-003 functions as a carrier-generation layer.
Furthermore,
In contrast, the light-emitting device 2-1 in which the first electron-transport layer is formed of a single material having both an electron-transport property and a hole-transport property showed more favorable drive voltage characteristics than every light-emitting device in which the first electron-transport layer is formed of two materials although the HOMO level of the single material is approximately −5.63 eV. This shows that the material included in the first electron-transport layer is preferably a single material having both an electron-transport property and a hole-transport property.
Thus, the use of the structure of the present invention can provide a light-emitting device having high emission efficiency, low drive voltage, and favorable characteristics.
Described in this example are specific methods for fabricating a light-emitting device 3-1 and a light-emitting device 3-2 of embodiments of the present invention and characteristics of the light-emitting devices.
Structural formulae of main compounds used in this example are shown below. 05251
First, 100-nm-thick silver (Ag) and 10 nm-thick indium tin oxide containing silicon oxide (ITSO) were stacked sequentially from the substrate side by a sputtering method as a reflective electrode and a transparent electrode, respectively, over a glass substrate, 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, baking was performed at 200° C. for one hour, and then UV ozone treatment was performed for 370 seconds.
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 substrate 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 a fluorine-containing electron acceptor material with 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 20 nm, whereby a first hole-transport layer was formed.
Then, over the first hole-transport layer, 4,8-bis[3-(dibenzothiophen-4-yl)phenyl]-[1]benzofuro[3,2-d]pyrimidine (abbreviation: 4,8mDBtP2Bfpm) represented by Structural Formula (ii) above, 9-(2-naphthyl)-9′-phenyl-9H,9′H-3,3′-bicarbazole (abbreviation: βNCCP) represented by Structural Formula (iii) above, and [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)) represented by Structural Formula (iv) above were deposited by co-evaporation to a thickness of 40 nm such that the weight ratio of 4,8mDBtP2Bfpm to βNCCP and Ir(ppy)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 25 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 (vi) above and 1-(9,9′-spirobi[9H-fluoren]-2-yl)-1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine (abbreviation: 2hppSF) 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 2hppSF was 1:1, copper phthalocyanine (abbreviation: CuPc) represented by Structural Formula (viii) above was deposited by evaporation to a thickness of 2 nm, and 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, whereby an intermediate layer was formed.
Over the intermediate layer, PCBBiF was deposited by evaporation to a thickness of 40 nm, whereby a second hole-transport layer was formed.
Over the second hole-transport layer, 4,8mDBtP2Bfpm, βNCCP, and Ir(ppy)2(mbfpypy-d3) were deposited by co-evaporation to a thickness of 40 nm such that the weight ratio of 4,8mDBtP2Bfpm to βNCCP and Ir(ppy)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.
Over the second electron-transport layer, 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 2:1, 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. In this manner, the light-emitting device of one embodiment of the present invention was fabricated. Over the second electrode 102, 4,4 ′,4″-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation: DBT3P-II) represented by Structural Formula (ix) 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 3-1 was fabricated.
The light-emitting device 3-2 was fabricated in a manner similar to that of the light-emitting device 3-1 except that the material of the first electron-transport layer in the light-emitting device 3-1 was replaced by 3,6-bis(diphenylamino)-9-[4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl]-9H-carbazole (abbreviation: DACT-II) represented by Structural Formula (xvi) above.
Device structures of the light-emitting devices 3-1 and 3-2 and the HOMO and LUMO levels of the main organic compounds used in the light-emitting devices are shown below. Note that the HOMO level and the LUMO level were obtained through cyclic voltammetry (CV) measurement in a manner similar to that of Example 1.
As shown above, the organic compounds each having a HOMO level greater than or equal to −5.9 eV and less than or equal to −5.0 eV are used in the first electron-transport layers in the light-emitting devices 3-1 and 3-2. The first layer of mPPhen2P: 2hppSF=1:1 formed in the intermediate layer is a film blocking holes. Furthermore, 2hppSF has an acid dissociation constant pKa of 13.95 and is an organic compound having strong basicity with a pKa of 8 or more. In addition, mPPhen2P, which is an organic compound having an electron-transport property and a LUMO level greater than or equal to −3.0 eV and less than or equal to −2.0 eV, is used in the first layer.
Here, an electron spin resonance spectrum of a thin film of mPPhen2P and 2hppSF that was deposited by co-evaporation to a thickness of 50 nm over a quartz substrate such that the weight ratio of mPPhen2P to 2hppSF was 1:1 was measured at room temperature, revealing that a signal was hardly observed at g-factors of approximately 2.00 and the spin density was 6.6×1016 spins/cm3. This means that 2hppSF does not almost exhibit an electron-donating property with respect to mPPhen2P. The second layer is a layer including PCBBiF, which is an organic compound having a hole-transport property, and OCHD-003 exhibiting an electron-acceptor property and is a carrier-generation layer in which charge separation occurs by voltage application.
Here, an electron spin resonance spectrum of a thin film of PCBBiF and OCHD-003 that was 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 was measured at room temperature, revealing that a signal was observed at a g-factor of approximately 2.00 and the spin density was 5×1019 spins/cm3. This means that OCHD-003 exhibits an electron-accepting property with respect to PCBBiF and the layer including PCBBiF and OCHD-003 functions as a carrier-generation layer.
Thus, the use of the structure of the present invention was able to provide the light-emitting devices having low drive voltage and favorable characteristics.
This is presumably because DACT-II showing a TADF property can reduce the influence of excitons generated by carrier recombination in the first electron-transport layer.
Described in this example are specific methods for fabricating a light-emitting device 4 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 sequentially from the substrate side by a sputtering method as a reflective electrode and a transparent electrode, respectively, over a glass substrate, 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, baking was performed at 200° C. for one hour, and then UV ozone treatment was performed for 370 seconds.
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 substrate 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 a fluorine-containing electron acceptor material with 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 (xvii) above, 9-(2-naphthyl)-9′-phenyl-9H,9′H-3,3′-bicarbazole (abbreviation: βNCCP) represented by Structural Formula (iii) above, and [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)) represented by Structural Formula (xviii) above were deposited by co-evaporation to a thickness of 40 nm such that the weight ratio of 8mpTP-4mDBtPBfpm to βNCCP and Ir(5mppy-d3)2(mbfpypy-d3) was 0.5:0.5:0.1, whereby a first light-emitting layer was formed.
Next, 3,6-bis(diphenylamino)-9-[4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl]-9H-carbazole (abbreviation: DACT-II) represented by Structural Formula (xvi) 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 (vi) above and 1-(2 ′,7′-di-tert-butyl-9,9′-spirobi[9H-fluoren]-2-yl)-1,3,4,6, 7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine (abbreviation: 2′,7′tBu-2hppSF) represented by Structural Formula (xix) above were deposited by co-evaporation to a thickness of 5 nm such that the weight ratio of mPPhen2P to 2′,7′tBu-2hppSF was 1:1, copper phthalocyanine (abbreviation: CuPc) represented by Structural Formula (viii) above was deposited by evaporation to a thickness of 2 nm, and 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, whereby 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, βNCCP, 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 βNCCP and Ir(5mppy-d3)2(mbfpypy-d3) was 0.5:0.5:0.1, whereby a second light-emitting layer was formed.
Then, 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 20 nm, and mPPhen2P was further deposited by evaporation to a thickness of 20 nm, whereby a second electron-transport layer was formed.
Over the second electron-transport layer, 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 2:1, 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. In this manner, the light-emitting device of one embodiment of the present invention was fabricated. Over the second electrode 102, 4,4 ′,4″-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation: DBT3P-II) represented by Structural Formula (ix) 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 device structure of the light-emitting device 4 and the HOMO and LUMO levels of the main organic compounds used in the light-emitting device are shown below. Note that the HOMO level and the LUMO level were obtained through cyclic voltammetry (CV) measurement in a manner similar to that of Example 1.
Thus, the use of the structure of the present invention was able to provide the light-emitting device having low drive voltage and favorable characteristics.
Here, the organic compound having a HOMO level greater than or equal to −5.9 eV and less than or equal to −5.0 eV is used in the first electron-transport layer in the light-emitting device 4. The first layer of mPPhen2P:2′, 7′tBu-2hppSF=1:1 formed in the intermediate layer is a film blocking holes. Furthermore, 2′,7′tBu-2hppSF has an acid dissociation constant pKa of 14.18 and is an organic compound having strong basicity with a pKa of 8 or more. In addition, mPPhen2P, which is an organic compound having an electron-transport property and a LUMO level greater than or equal to −3.0 eV and less than or equal to −2.0 eV, is used in the first layer.
Here, an electron spin resonance spectrum of a thin film of mPPhen2P and 2′,7′tBu-2hppSF that was deposited by co-evaporation to a thickness of 100 nm over a quartz substrate such that the weight ratio of mPPhen2P to 2′,7′tBu-2hppSF was 1:1 was measured at room temperature, revealing that a signal was not observed at g-factors of approximately 2.00 and the spin density was lower than 1×1016 spins/cm3, which is the detection limit. Note that the measurement of electron spin resonance spectrum using ESR spectroscopy 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. This means that 2′,7′tBu-2hppSF does not exhibit an electron-donating property with respect to mPPhen2P.
Similarly, an electron spin resonance spectrum of a thin film of 2′, 7′tBu-2hppSF that was deposited by evaporation to a thickness of 100 nm was measured at room temperature, revealing that a signal was hardly observed at g-factors of approximately 2.00 and the number of spins was lower than the lower detection limit of 4×1011 spins.
Furthermore, an electron spin resonance spectrum of a thin film of PCBBiF and OCHD-003 that was 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 was measured similarly, revealing that a signal was observed at a g-factor of approximately 2.00 and the spin density was 5×1019 spins/cm3. Note that the measurement of electron spin resonance spectrum using ESR spectroscopy was performed with an electron spin resonance spectrometer JES FA300 (manufactured by JEOL Ltd.) in a manner similar to that of Example 1. This means that OCHD-003 exhibits an electron-accepting property with respect to PCBBiF and the layer including PCBBiF and OCHD-003 functions as a carrier-generation layer. The second layer is a layer including PCBBiF and OCHD-003 and is a carrier-generation layer in which charge separation occurs by voltage application.
Next, electron spin resonance spectra of the light-emitting device 4 were measured under three conditions: before driving, during driving (at a voltage of 10 V), and after driving. Note that the measurements of electron spin resonance spectra using ESR spectroscopy before driving, during driving, and after driving were performed with an electron spin resonance spectrometer E500 (manufactured by Bruker Corporation).
The measurements were performed at room temperature in a nitrogen atmosphere 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. The application voltage during driving was 10 V, at which light emits at 49000 cd/m2. The results are shown in
In
Next, between the first electrode and the second electrode having the same structure as those of the light-emitting device 4 formed over a glass substrate, only 2′,7′tBu-2hppSF was deposited by evaporation to a thickness of 100 nm to fabricate a sample 1, and electron spin resonance spectra of the sample 1 were measured under three conditions: before driving, during driving (at a voltage of 10 V), and after driving in a manner similar to that of the light-emitting device 4. The application voltage during driving was 10 V. The results are shown in
In
These results show a high probability that the spins detected by the measurement of the light-emitting device 4 are derived from the hole-injection layer, the second layer of the intermediate layer, and the electron-injection layer and are not derived from the first layer of the intermediate layer.
In this reference example, materials having different acid dissociation constants pKa were used for a layer on the first electron-transport layer side in the intermediate layer, and characteristics were evaluated. The results are described.
As illustrated in
The light-emitting devices A to E have the same structure except the material of the first layer 814. The first layer 814 was formed by co-evaporation of an organic compound having the same electron-transport property and an organic compound having an individual acid dissociation constant pKa at a weight ratio of 1:1. The organic compounds having individual acid dissociation constants pKa used in the first layers 814 of the light-emitting devices A to E are an organic compound A to an organic compound E
Moreover, a comparative light-emitting device having a structure similar to that of the light-emitting devices A to E was fabricated using lithium oxide (Li2O) instead of the organic compound having the individual acid dissociation constant pKa of the first layer 814.
Emission characteristics of the light-emitting devices A to E were measured. The ratio in external quantum efficiency of each device at a current density of 50 mA/cm2 was calculated with the assumption that the external quantum efficiency of the comparative light-emitting device was 100%. The results are shown in
According to
In this reference example, the result of examining the electron-transport property of the material used in the DLL are described. The structural formulae of organic compounds used in the reference example 2 are shown below.
The electron-transport property of the material used in the DLL was examined by fabricating an electronic device that makes only electrons flow (hereinafter referred to as an electron-only device) and measuring the relation between current density and voltage.
First, 100-nm-thick silver (Ag) and 85-nm-thick indium tin oxide containing silicon oxide (ITSO) were stacked over a glass substrate by a sputtering method.
Next, in pretreatment for forming the light-emitting device over a substrate, the surface of the substrate was washed with water, baking was performed at 200° C. for one hour, and then UV ozone treatment was performed for 370 seconds.
After that, the substrate was transferred into a vacuum evaporation apparatus where the pressure was reduced to approximately 10−4 Pa, and was subjected to vacuum baking at 170° C. for 60 minutes in a heating chamber of the vacuum evaporation apparatus, and then the substrate was cooled down for approximately 30 minutes.
Next, the substrate provided with Ag and ITSO was fixed to a substrate holder provided in the vacuum evaporation apparatus such that the surface on which the Ag and
ITSO were formed faced downward. Then, aluminum (Al) was deposited by evaporation to form a first electrode with a size of 2 mm×2 mm. Over the first electrode, 4,7-di-1-pyrrolidinyl-1,10-phenanthroline (abbreviation: Pyrrd-Phen) represented by Structural Formula (xvii) above and aluminum (Al) were deposited by co-evaporation to a thickness of 1 nm such that the weight ratio of Pyrrd-Phen to Al was 1:0.03, whereby a layer 1 was formed.
Over the layer 1, 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 50 nm to form a layer 2.
Next, over the layer 2, 2,2′-(1,3-phenylene)bis(9-phenyl-1,10-phenanthroline) (abbreviation: mPPhen2P) represented by Structural Formula (vi) above was deposited by evaporation to a thickness of 10 nm to form a layer 3.
Over the layer 3, 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 2:1, whereby a layer 4 was formed. Over the layer 4, aluminum was deposited by evaporation to a thickness of 100 nm to form a second electrode. Thus, an EOD1 was fabricated.
An EOD2 was fabricated in a manner similar to that of the EOD1 except that the third layer in the EOD1 was formed by depositing mPPhen2P and lithium oxide (Li2O) by co-evaporation to a thickness of 10 nm such that the volume ratio of mPPhen2P to LizO was 1:0.01.
An EOD3 was fabricated in a manner similar to that of the EOD1 except that the third layer in the EOD1 was formed by depositing mPPhen2P and 1-(9,9′-spirobi[9H-fluoren]-2-yl)-1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine (abbreviation: 2hppSF) represented by Structural Formula (vii) above by co-evaporation to a thickness of 10 nm such that the volume ratio of mPPhen2P to 2hppSF was 1:1.
The device structures of the EOD1 to EOD3 are shown in the table below.
It was found that the layer 3 of the EOD3 is a layer that blocks holes and is also a layer that has an especially high electron-transport property and is formed of materials capable of being suitably used in the DLL.
This application is based on Japanese Patent Application Serial No. 2022-192043 filed with Japan Patent Office on Nov. 30, 2022 and Japanese Patent Application Serial No. 2023-060404 filed with Japan Patent Office on Apr. 3, 2023, the entire contents of which are hereby incorporated by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2022-192043 | Nov 2022 | JP | national |
| 2023-060404 | Apr 2023 | JP | national |
