Patent Application
20160118605
1. Field of the Invention
One embodiment of the present invention relates to a light-emitting element in which a light-emitting layer capable of emitting light by application of an electric field is provided between a pair of electrodes. Specifically, one embodiment of the present invention relates to a light-emitting element in which a light-emitting layer includes an iridium complex. One embodiment of the present invention relates to a light-emitting device, a display device, an electronic device, and a lighting device each including the above light-emitting element.
Note that one embodiment of the present invention is not limited to the above technical field. The technical field of one embodiment of the invention disclosed in this specification and the like relates to an object, a method, or a manufacturing method. Alternatively, the technical field of one embodiment of the present invention relates to a process, a machine, manufacture, or a composition of matter. Specifically, examples of the technical field of one embodiment of the present invention disclosed in this specification include a semiconductor device, a display device, a liquid crystal display device, a light-emitting device, a lighting device, a power storage device, a memory device, a method for driving any of them, and a method for manufacturing any of them.
2. Description of the Related Art
A light-emitting element having a structure in which an organic compound that is a light-emitting substance is provided between a pair of electrodes (also referred to as an organic EL element) has attracted attention as a next-generation flat panel display in terms of characteristics such as being thin and light in weight, high-speed response, and low voltage driving. In addition, a display using such an organic EL element is superior in contrast, image quality, and wide viewing angle.
Various organic compounds to be used for an organic EL element have been researched and developed. For example, as an organic compound that is a light-emitting substance, an organometallic complex having iridium (Ir) or the like as a central metal has attracted attention.
In manufacture of an organic EL element, the purity of an organic compound is an important factor. For example, in the case where an organic EL element is fabricated with the use of an organic compound containing an impurity such as a solvent used in synthesis, the characteristics of the organic EL element (e.g., drive voltage characteristics, emission efficiency characteristics, or a lifetime) might be poor. Accordingly, a material with a reduced amount of impurity, which is subjected to purification by sublimation, is generally used as an organic compound for an organic EL element. The purification by sublimation can remove a solvent remaining after synthesis or a small amount of impurity such as a halide (see, for example, Patent Document 1).
However, even when an organic EL element is fabricated with the use of the organic compound subjected to the purification by sublimation, the reliability of the organic EL element might be low.
[Patent Document 1] Japanese Published Patent Application No. 2011-216903
In one embodiment of the present invention, a long-life light-emitting element is provided by reducing a specific kind of impurity, particularly an impurity originating in an iridium complex, in the light-emitting element. In one embodiment of the present invention, a novel light-emitting element is provided.
Note that the descriptions of these objects do not disturb the existence of other objects. In one embodiment of the present invention, there is no need to achieve all the objects. Other objects will be apparent from and 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 element including an iridium complex. The iridium complex includes an iridium metal and a ligand coordinated to the iridium metal. In analysis of the light-emitting element by liquid chromatography mass spectrometry using a chromatograph of a photodiode array detector, the proportion of the peak area of a ligand not coordinated to the iridium metal to the peak area of the iridium complex is greater than or equal to 0% and less than or equal to 10%.
Another embodiment of the present invention is a light-emitting element including an iridium complex. The iridium complex includes an iridium metal and a ligand coordinated to the iridium metal. In analysis of the light-emitting element by liquid chromatography mass spectrometry, a precursor ion of the iridium complex, a first fragment ion of the iridium complex, and a second fragment ion of the iridium complex are detected by a mass spectrometric detector and a photodiode array detector. The first fragment ion detected by the mass spectrometric detector includes the iridium metal. The second fragment ion detected by the mass spectrometric detector does not include the iridium metal. A chromatograph of the photodiode array detector includes a first peak corresponding to the precursor ion, a second peak corresponding to the first fragment ion, and a third peak corresponding to the second fragment ion. The proportion of the area of the third peak to the area of the first peak is greater than or equal to 0% and less than or equal to 10%.
Another embodiment of the present invention is a light-emitting element including an iridium complex. The iridium complex includes an iridium metal and a ligand coordinated to the iridium metal. In analysis of the light-emitting element by liquid chromatography mass spectrometry using a chromatograph of a photodiode array detector, the proportion of the peak area of a ligand not coordinated to the iridium metal to the peak area of the iridium complex is greater than or equal to 0% and less than or equal to 5%.
Another embodiment of the present invention is a light-emitting element including an iridium complex. The iridium complex includes an iridium metal and a ligand coordinated to the iridium metal. In analysis of the light-emitting element by liquid chromatography mass spectrometry, a precursor ion of the iridium complex, a first fragment ion of the iridium complex, and a second fragment ion of the iridium complex are detected by a mass spectrometric detector and a photodiode array detector. The first fragment ion detected by the mass spectrometric detector includes the iridium metal. The second fragment ion detected by the mass spectrometric detector does not include the iridium metal. A chromatograph of the photodiode array detector includes a first peak corresponding to the precursor ion, a second peak corresponding to the first fragment ion, and a third peak corresponding to the second fragment ion. The proportion of the area of the third peak to the area of the first peak is greater than or equal to 0% and less than or equal to 5%.
Another embodiment of the present invention is a light-emitting element including an iridium complex. The iridium complex includes an iridium metal and a ligand coordinated to the iridium metal. In analysis of the light-emitting element by liquid chromatography mass spectrometry using a chromatograph of a photodiode array detector, the proportion of the peak area of a ligand not coordinated to the iridium metal to the peak area of the iridium complex is greater than or equal to 0% and less than or equal to 1%.
Another embodiment of the present invention is a light-emitting element including an iridium complex. The iridium complex includes an iridium metal and a ligand coordinated to the iridium metal. In analysis of the light-emitting element by liquid chromatography mass spectrometry, a precursor ion of the iridium complex, a first fragment ion of the iridium complex, and a second fragment ion of the iridium complex are detected by a mass spectrometric detector and a photodiode array detector. The first fragment ion detected by the mass spectrometric detector includes the iridium metal. The second fragment ion detected by the mass spectrometric detector does not include the iridium metal. A chromatograph of the photodiode array detector includes a first peak corresponding to the precursor ion, a second peak corresponding to the first fragment ion, and a third peak corresponding to the second fragment ion. The proportion of the area of the third peak to the area of the first peak is greater than or equal to 0% and less than or equal to 1%.
Another embodiment of the present invention is a light-emitting device that includes the above-described light-emitting element and a color filter. Another embodiment of the present invention is an electronic device that includes the above-described light-emitting element or the above light-emitting device and a housing or a touch sensor function. Another embodiment of the present invention is a lighting device that includes the above-described light-emitting element or the above light-emitting device and a housing.
One embodiment of the present invention makes it possible to provide a long-life light-emitting element by reducing a specific kind of impurity, particularly an impurity originating in an iridium complex, in the light-emitting element. One embodiment of the present invention makes it possible to provide a novel light-emitting element.
Note that one embodiment of the present invention is not limited to these effects. For example, depending on circumstances or conditions, one embodiment of the present invention might produce an effect other than these effects. Furthermore, depending on circumstances or conditions, one embodiment of the present invention might not produce any of the above effects.
Embodiments of the present invention will be explained below with reference to the drawings. Note that one embodiment of the present invention is not limited to the description given below, and various changes and modifications can be made without departing from the spirit and scope of the present invention. Therefore, one embodiment of the present invention should not be construed as being limited to the description in Embodiments or Examples.
Note that the position, the size, the range, or the like of each structure illustrated in drawings and the like is not accurately represented in some cases for simplification. Therefore, one embodiment of the disclosed invention is not necessarily limited to the position, the size, the range, or the like disclosed in the drawings and the like.
Ordinal numbers such as “first” and “second” in this specification and the like are used for convenience and do not denote the order of steps or the stacking order of layers. Therefore, for example, description can be made even when “first” is replaced with “second” or “third”, as appropriate. In addition, the ordinal numbers in this specification and the like are not necessarily the same as those which specify one embodiment of the present invention.
In describing structures of the invention with reference to the drawings in this specification and the like, common reference numerals are used for the same portions in different drawings.
In this specification and the like, the terms “film” and “layer” can be interchanged with each other depending on the case or circumstances. For example, in some cases, the term “conductive film” can be used instead of the term “conductive layer,” and the term “insulating layer” can be used instead of the term “insulating film”.
An iridium complex in this specification and the like might have a structural isomer such as a stereoisomer depending on the kind of its ligand. In the category of the iridium complex described in this specification and the like, the iridium complex and its structural isomer are included.
In this embodiment, a light-emitting element of one embodiment of the present invention will be described below with reference to
Specifically, a light-emitting element 100 in
In this embodiment, the lower electrode 104 is used as an anode and the upper electrode 114 is used as a cathode. The lower electrode 104 is formed over a substrate 102. The light-emitting layer 110 contains an iridium complex as a light-emitting substance.
By application of a voltage to the light-emitting element 100, holes injected from the lower electrode 104 side and electrons injected from the upper electrode 114 side recombine in the light-emitting layer 110 to raise the light-emitting substance contained in the light-emitting layer 110 to an excited state. The light-emitting substance in the excited state emits light when the excited light-emitting substance relaxes to the ground state.
It is desirable that the light-emitting element 100 hardly suffer a reduction in emission efficiency due to long preservation or long driving. In other words, it is desirable that the light-emitting element 100 have a long lifetime, or high reliability. To achieve high reliability of the light-emitting element 100, the EL layer 108 is preferably formed using an organic compound containing few impurities. For example, it is preferable that the content of an impurity such as an element contained in a raw material used in synthesis of the organic compound (e.g., a halogen element) be low.
However, the light-emitting element 100 has sometimes low reliability even when including the organic compound in which a halogen element is reduced.
In view of the above, in the light-emitting element 100 of one embodiment of the present invention, an impurity originating in the iridium complex included in the light-emitting layer 110 of the EL layer 108 is reduced. The iridium complex in the light-emitting layer 110 has an iridium metal and a ligand coordinated to the iridium metal. When the light-emitting element 100 is analyzed by liquid chromatography mass spectrometry (LC/MS) using a chromatograph of a photodiode array (PDA) detector, the proportion of the peak area of a ligand not coordinated to the iridium metal to the peak area of the iridium complex is 10% or less, preferably 5% or less, further preferably 1% or less. It is preferable that the ligand not coordinated to the iridium metal not be contained in the light-emitting element 100. In other words, the minimum proportion of the peak area of the ligand not coordinated to the iridium metal to the peak area of the iridium complex is 0%.
The iridium complex contained in the light-emitting layer 110 includes an iridium metal and a ligand coordinated to the iridium metal. In analysis of the light-emitting element 100 by liquid chromatography mass spectrometry, a precursor ion of the iridium complex, a first fragment ion of the iridium complex, and a second fragment ion of the iridium complex are detected by a mass spectrometric (MS) detector and a photodiode array detector. The first fragment ion detected by the MS detector includes the iridium metal. The second fragment ion detected by the MS detector does not include the iridium metal. A chromatograph of the photodiode array detector includes a first peak corresponding to the precursor ion, a second peak corresponding to the first fragment ion, and a third peak corresponding to the second fragment ion. The proportion of the area of the third peak to the area of the first peak is less than or equal to 10%, preferably less than or equal to 5%, further preferably less than or equal to 1%.
The use of the above iridium complex as the iridium complex of the light-emitting layer 110 leads to improved reliability of the light-emitting element 100.
Light-emitting elements (Samples 1 and 2) each corresponding to the light-emitting element 100 illustrated in
Specific element structures of Samples 1 and 2 fabricated in this embodiment are shown in Table 1, and structures and abbreviations of the compounds used are shown below.
First, over the substrate 102, indium tin oxide containing silicon oxide (abbreviation: ITSO) was deposited as the lower electrode 104 by a sputtering method. Note that the thickness of the lower electrode 104 was 100 nm and the area of the lower electrode 104 was 4 mm2 (2 mm×2 mm).
Then, for pretreatment before deposition of an organic compound layer by evaporation, the lower electrode 104 side of the substrate 102 provided with the lower electrode 104 was washed with water, baking was performed at 200° C. for 1 hour, and then UV ozone treatment was performed on a surface of the lower electrode 104 for 370 seconds.
After that, the substrate 102 was transferred into a vacuum evaporation apparatus where the pressure had been 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 102 was cooled down for approximately 30 minutes.
Next, the substrate 102 was fixed to a holder provided in the vacuum evaporation apparatus so that a surface of the substrate over which the lower electrode 104 was formed faced downward. In this embodiment, by a vacuum evaporation method, the hole-injection layer 131, the hole-transport layer 132, the light-emitting layer 110, the electron-transport layer 133(1), the electron-transport layer 133(2), the electron-injection layer 134, and the upper electrode 114 were sequentially formed. The fabrication method will be described in detail below.
First, after reducing the pressure of the vacuum evaporation apparatus to 10−4 Pa, 4,4′,4″-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation: DBT3P-II) and molybdenum oxide were deposited by co-evaporation in a weight ratio of 2:1 (=DBT3P-II: molybdenum oxide), whereby the hole-injection layer 131 was formed over the lower electrode 104. Note that the thickness of the hole-injection layer 131 was 20 nm.
Then, the hole-transport layer 132 was formed over the hole-injection layer 131. As the hole-transport layer 132, 4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP) was deposited by evaporation. Note that the thickness of the hole-transport layer 132 was 20 nm.
Next, the light-emitting layer 110 was formed over the hole-transport layer 132. As the light-emitting layer 110, 2-[3′-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTBPDBq-II), 4,4′-di(1-naphthyl)-4″-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBNBB), and bis(2,3,5-triphenylpyrazinato)(dipivaloylmethanato)iridium(III) (abbreviation: Ir(tppr)2(dpm)) were deposited by co-evaporation in a weight ratio of 0.7:0.3:0.05 (=2mDBTBPDBq-II: PCBNBB: Ir(tppr)2(dpm)). Note that the thickness of the light-emitting layer 110 was 40 nm.
In the light-emitting layer 110, 2mDBTBPDBq-II is a host material, PCBNBB is an assist material, and Ir(tppr)2(dpm) is an iridium complex serving as a guest material. Note that the host material is a carrier-transport material, and an electron-transport material was used as the host material. The assist material is a carrier-transport material, and a hole-transport material was used as the assist material. The guest material was a light-emitting material (a material containing a light-emitting substance). Note that it is preferable that the level of triplet excitation energy (T1 level) of each of the host material and the assist material be higher than the T1 level of the guest material. When the T1 level of each of the host material and the assist material is lower than that of the guest material, the triplet excitation energy of the guest material, which is to contribute to light emission, is quenched by the host material and the assist material and accordingly the emission efficiency is reduced in some cases. Carrier balance can be controlled by changing a mixing ratio of the host material and the assist material.
After that, over the light-emitting layer 110, 2mDBTBPDBq-II was deposited by evaporation to a thickness of 20 nm as the electron-transport layer 133(1). Then, over the electron-transport layer 133(1), bathophenanthroline (abbreviation: Bphen) was deposited by evaporation to a thickness of 15 nm as the electron-transport layer 133(2). Then, over the electron-transport layer 133(2), lithium fluoride (LiF) was deposited by evaporation to a thickness of 1 nm as the electron-injection layer 134.
Then, over the electron-injection layer 134, aluminum (Al) was deposited by evaporation to a thickness of 200 nm as the upper electrode 114.
Next, a sealing substrate (not shown) was prepared, and each of the light-emitting elements over the substrate 102 fabricated as described above was sealed by being bonded to the sealing substrate in a glove box in a nitrogen atmosphere so as not to be exposed to the air (specifically, a sealant was applied to surround the element and irradiated with ultraviolet light having a wavelength of 365 nm at 6 J/cm2, and then, heat treatment was performed at 80° C. for 1 hour).
Note that in all the above evaporation steps for Samples 1 and 2, a resistive heating method was used as an evaporation method.
Through the above-described process, Sample 1 and Sample 2 were manufactured.
Next, reliability tests were performed on Samples 1 and 2. In the reliability tests, Samples 1 and 2 were driven under the conditions where the initial luminance was 5000 cd/m2 and the current density was constant.
The results in
Next, an impurity in the EL layer 108 of each of Samples 1 and 2 was analyzed. Note that for analysis of an impurity in Sample 1, a sample that was different from Sample 1 and was formed over the same substrate as Sample 1 was used; for analysis of an impurity in Sample 2, a sample that was different from Sample 2 and was formed over the same substrate as Sample 2 was used. In each of the samples for the impurity analysis, the area of the lower electrode 104 was approximately 12 cm2 (3.5 cm×3.3 cm). In other words, the samples for the impurity analysis had the same materials and structures as Samples 1 and 2, but were different from Samples 1 and 2 in the area of the lower electrode 104. The samples for the impurity analysis were not driven; thus, the obtained results were not the analysis results of deteriorated objects produced by driving, but the analysis results of an impurity that had been contained from before driving. Here, the sample for the impurity analysis that was fabricated over the same substrate as Sample 1 is regarded as Sample 1 for convenience. The same applies to Sample 2.
An impurity in Samples 1 and 2 was analyzed by LC/MS.
In the LC/MS analysis, LC separation was performed using ACQUITY UPLC System manufactured by Waters Corporation, and detection was performed using a PDA detector and an MS detector. Note that a PDA eλ detector manufactured by Waters Corporation was used as the PDA detector, and Xevo G2 Tof MS manufactured by Waters Corporation was used as the MS detector. The measurement range of the Xevo G2 Tof MS detector manufactured by Waters Corporation, which used in the analysis, was m/z=100 or more.
ACQUITY UPLC BEH C8 (2.1×100 mm, 1.7 μm) was used as a column for the LC separation, and the column temperature was 40° C. Acetonitrile was used for Mobile Phase A and a 0.1% formic acid aqueous solution was used for Mobile Phase B.
Samples for the LC/MS analysis were obtained in the following manner: aluminum that was the upper electrode 114 of each of Samples 1 and 2 was peeled with the use of a Kapton tape (registered trademark); a substance remaining over the substrate 102 was dissolved in chloroform, so that a chloroform solution was obtained; and the chloroform solution was diluted with acetonitrile to a given concentration. The injection amount of the analysis sample was 5.0 μL in the LC/MS analysis.
The LC separation of the analysis samples was performed. In the LC separation, a gradient method in which the ratio between mobile phases is changed was employed. The ratio of Mobile Phase A to Mobile Phase B was 60:40 for 0 to 1 minute after the start of the measurement, and then the ratio of Mobile Phase A to Mobile Phase B was changed linearly such that the ratio in the 15th minute was 95:5. That is, the measurement time was 15 minutes.
With the PDA detector, detection was performed in the range of 210 nm to 800 nm, and the detection interval was 1.2 nm.
In the MS analysis, ionization was carried out by an electrospray ionization (ESI) method. At this time, the capillary voltage and the sample cone voltage were set to 3.0 kV and 30 V, respectively, and detection was performed in a positive mode. The mass range for the measurement was m/z=100 to 1300.
The LC separation was performed under the above conditions, and a component which underwent the ionization was collided with an argon gas in a collision cell. Energy (collision energy) for the collision with argon was 6 eV, which allowed observation of product ions.
The chloroform used for fabrication of the analysis samples was diluted with acetonitrile to give a solution, and the solution was analyzed to obtain a PDA base-line (or background: BG) chromatogram. In
As shown in
Next, the PDA chromatograms were analyzed with a focus on Ir(tppr)2(dpm). The base line was subtracted in the analysis of the PDA chromatograms.
In
That is, an MS spectrum including a peak derived from an Ir compound was obtained only from the peak a5, and the peak a6 derived from a compound not containing Ir but originating in Ir(tppr)2(dpm) was observed in
Next, with the use of the results of LC/MS analysis shown in
As shown in Table 2, in Sample 1, on the assumption that the total peak area of substances originating in the iridium complex Ir(tppr)2(dpm) was 100%, the proportion of the peak area (a6) of a ligand not coordinated to the iridium metal to the peak area (a5) of the iridium complex was 0.8%. In Sample 2, on the assumption that the total peak area of substances originating in the iridium complex Ir(tppr)2(dpm) was 100%, the proportion of the peak area (a6) of a ligand not coordinated to the iridium metal to the peak area (a5) of the iridium complex was 10.6%.
As described above, the content of the ligand not coordinated to the iridium metal, which is an impurity originating in the iridium complex in the light-emitting layer 110, was different between Samples 1 and 2. This difference in the content of the ligand not coordinated to the iridium metal presumably resulted in the difference in reliability between Samples 1 and 2 that is shown in
The ligand not coordinated to the iridium metal in Samples 1 and 2 might be contained in the iridium complex before deposition by evaporation, or might be produced in the EL layer 108 through decomposition during or after deposition by evaporation. Thus, an impurity in a material originating in the iridium complex before deposition by evaporation was analyzed.
Samples for the LC/MS analysis were obtained in the following manner: the iridium complex (Material X1) before deposition by evaporation was dissolved in chloroform, so that a chloroform solution was obtained; and the chloroform solution was diluted with acetonitrile to a given concentration. The injection amount of the analysis sample was 5.0 μL in the LC/MS analysis. The method of the LC/MS analysis was the same as that employed for Samples 1 and 2 above, except for the conditions of the LC separation. In the LC separation of Material X1, acetonitrile was used for Mobile Phase A and a 0.1% formic acid aqueous solution was used for Mobile Phase B. A gradient method in which the ratio between mobile phases is changed was employed. The ratio of Mobile Phase A to Mobile Phase B was 75:25 for 0 to 1 minute after the start of the measurement; the ratio of Mobile Phase A to Mobile Phase B was changed linearly such that the ratio in the 4th minute was 90:10; and then, the ratio of Mobile Phase A to Mobile Phase B was changed linearly such that the ratio in the 10th minute was 95:5. That is, the total measurement time was 10 minutes.
In an MS spectrum obtained in the LC/MS analysis of Material X1, peaks were observed at m/z=991, m/z=1145, m/z=1023, and m/z=915. With the use of the peak areas, impurities contained in Material X1 were analyzed, and the results are shown in Table 3.
As shown in Table 3, Material X1, which was the iridium complex used in the light-emitting layer 110 of Samples 1 and 2, had high purity, and the existence of the ligand tppr serving as an impurity, which was confirmed in the light-emitting layer 110, was not confirmed in Material X1.
It was thus suggested that tppr, which was a ligand of Ir(tppr)2(dpm) and was contained in the light-emitting layer 110 of Sample 2 in a large amount, was produced in the EL layer 108 during or after deposition by evaporation.
Here, the components of the light-emitting element 100 in
The substrate 102 is used as a support of the light-emitting element 100. For the substrate 102, glass, quartz, plastic, or the like can be used, for example. Alternatively, a flexible substrate can be used. A flexible substrate is a substrate that can be bent; examples of the flexible substrate include a plastic substrate made of a polycarbonate, a polyarylate, or a polyethersulfone. A film (made of polypropylene, a polyester, poly(vinyl fluoride), poly(vinyl chloride), or the like), an inorganic vapor-deposited film, or the like can be used.
The substrate may be formed with any other material that can serve as a support in a fabrication process of the light-emitting element 100. The light-emitting element 100 can be formed using a variety of substrates, for example. The type of the substrate is not limited to a certain type. As the substrate, a semiconductor substrate (e.g., a single crystal substrate or a silicon substrate), an SOI substrate, a glass substrate, a quartz substrate, a plastic substrate, a metal substrate, a stainless steel substrate, a substrate including stainless steel foil, a tungsten substrate, a substrate including tungsten foil, a flexible substrate, an attachment film, paper including a fibrous material, a base material film, or the like can be used, for example. Examples of a glass substrate include a barium borosilicate glass substrate, an aluminoborosilicate glass substrate, and a soda lime glass substrate. Examples of the flexible substrate, the attachment film, the base film, and the like are substrates of plastics typified by polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyether sulfone (PES), and polytetrafluoroethylene (PTFE). Another example is a synthetic resin such as acrylic. Furthermore, polypropylene, polyester, polyvinyl fluoride, and polyvinyl chloride can be given as examples. Other examples are polyamide, polyimide, aramid, epoxy, an inorganic vapor deposition film, paper, and the like.
Alternatively, a flexible substrate may be used as the substrate, and the light-emitting element 100 may be provided directly on the flexible substrate. Alternatively, a separation layer may be provided between the substrate and the light-emitting element 100. The separation layer can be used when part or the whole of the light-emitting element 100 formed over the separation layer is completed, separated from the substrate, and transferred to another substrate. In such a case, the light-emitting element 100 can be transferred to a substrate having low heat resistance or a flexible substrate as well. For the above separation layer, a stack including inorganic films, which are a tungsten film and a silicon oxide film, or an organic resin film of polyimide or the like formed over a substrate can be used, for example.
In other words, after the light-emitting element 100 is formed using a substrate, the light-emitting element 100 may be transferred to another substrate. Examples of a substrate to which the light-emitting element 100 is transferred include, in addition to the above-described substrates, a paper substrate, a cellophane substrate, an aramid film substrate, a polyimide substrate, a stone substrate, a wood substrate, a cloth substrate (including a natural fiber (e.g., silk, cotton, or hemp), a synthetic fiber (e.g., nylon, polyurethane, or polyester), a regenerated fiber (e.g., acetate, cupra, rayon, or regenerated polyester), or the like), a leather substrate, and a rubber substrate. By using such a substrate, the light-emitting element 100 with high durability, the light-emitting element 100 with high heat resistance, the light-emitting element 100 that is lightweight, or the light-emitting element 100 that is thin can be obtained.
As the lower electrode 104 and the upper electrode 114, a metal, an alloy, an electrically conductive compound, a mixture thereof, and the like can be used. Specific examples include indium oxide-tin oxide (ITO: indium tin oxide), indium oxide-tin oxide containing silicon or silicon oxide (ITSO), indium oxide-zinc oxide, indium oxide containing tungsten oxide and zinc oxide, gold (Au), platinum (Pt), nickel (Ni), tungsten (W), chromium (Cr), molybdenum (Mo), iron (Fe), cobalt (Co), copper (Cu), palladium (Pd), and titanium (Ti). In addition, any of the following materials can be used: elements that belong to Group 1 or Group 2 of the periodic table, that is, alkali metals such as lithium (Li) and cesium (Cs) or alkaline earth metals such as calcium (Ca) and strontium (Sr), magnesium (Mg), and alloys containing at least one of the metals (e.g., Mg—Ag and Al—Li); rare earth metals such as europium (Eu) and ytterbium (Yb), and alloys containing at least one of the metals; and graphene. The lower electrode 104 and the upper electrode 114 can be formed by, for example, a sputtering method, an evaporation method (including a vacuum evaporation method), or the like.
The light-emitting layer 110 contains at least an iridium complex as a light-emitting substance. The light-emitting layer 110 contains either or both of an electron-transport material and a hole-transport material in addition to the light-emitting substance. Although the light-emitting layer 110 included in the light-emitting element 100 in
An example of the iridium complex included in the light-emitting layer 110 is an iridium complex including two or more ligands each of which includes an aromatic heterocyclic compound containing at least one nitrogen atom.
Examples of the aromatic heterocyclic compound include imidazole, pyrazole, isothiazole, isoxazole, pyrazine, pyridine, pyrimidine, pyridazine, indazole, purine, quinoxaline, quinoline, isoquinoline, phthalazine, naphthyridine, quinazoline, cinnoline, pteridine, phenanthridine, acridine, perimidine, phenanthroline, phenazine, oxadiazole, thiadiazole, triazole, and triazine.
In the iridium complex included in the light-emitting element of one embodiment of the present invention, the nitrogen atom of the aromatic heterocyclic compound in the above ligand is coordinated to the iridium metal. Note that the ligand of the iridium complex does not necessarily include the above aromatic heterocyclic compound.
In the case where an impurity is produced during deposition by evaporation because of thermal decomposition or the like in the iridium complex, which is to be included in the light-emitting element of one embodiment of the present invention, the impurity might be mixed into a film after the deposition by evaporation. In the case where an impurity produced during the deposition by evaporation is mixed into the film after the deposition by evaporation, the iridium complex included in the light-emitting element might have a low purity. As a specific example of the impurity mixed into the light-emitting element, a ligand coordinated to the iridium metal of the iridium complex can be given.
In some cases, the above-described iridium complex is more easily decomposed when the coordinate bond between a nitrogen atom in the ligand and the iridium metal is weak. It can be presumed that when the aromatic heterocyclic compound of the ligand coordinated to the iridium metal contains two or more nitrogen atoms, the basicity of the ring becomes lower and the coordinate bond becomes weaker than when only one nitrogen atom is contained. Thus, an iridium complex whose ligand includes an aromatic heterocyclic compound containing two or more nitrogen atoms might easily suffer a reduction in purity through deposition by evaporation.
In other words, decomposition of a ligand and mixture thereof into the light-emitting element occur more easily in the case of using an iridium complex whose ligand includes an aromatic heterocyclic compound containing two or more nitrogen atoms than in the case of using an iridium complex whose ligand includes an aromatic heterocyclic compound containing one nitrogen atom. Thus, the lifetime of the light-emitting element can be extended by inhibiting mixture of a ligand of an iridium complex that includes an aromatic heterocyclic compound containing two or more nitrogen atoms.
Examples of the aromatic heterocyclic compound containing two or more nitrogen atoms include diazine and triazine. Specific examples of the aromatic heterocyclic compound containing two nitrogen atoms include imidazole, pyrazole, pyrazine, pyrimidine, pyridazine, indazole, purine, quinoxaline, phthalazine, naphthyridine, quinazoline, cinnoline, pteridine, phenanthridine, perimidine, phenanthroline, phenazine, oxadiazole, thiadiazole, triazole, and triazine.
As examples of the iridium complex that can be used in the light-emitting element of one embodiment of the present invention, iridium complexes represented by General Formulae (G1) to (G4) below can be given.
In General Formulae (G1) to (G4), each of R1 to R4 independently represents hydrogen, an alkyl group having 1 to 6 carbon atoms, or a substituted or unsubstituted aryl group having 1 to 10 carbon atoms and forming a ring, Ar represents a substituted or unsubstituted arylene group having 1 to 10 carbon atoms and forming a ring, and L represents a monoanionic ligand. Furthermore, n is 2 or 3, in is 0 or 1, and the sum of n and m is 3.
The monoanionic ligand represented by L in General Formulae (G1) to (G4) is preferably any of a monoanionic bidentate chelate ligand having a β-diketone structure, a monoanionic bidentate chelate ligand having a carboxyl group, a monoanionic bidentate chelate ligand having a phenolic hydroxyl group, and a monoanionic bidentate chelate ligand in which two ligand elements are both nitrogen.
As examples of the monoanionic ligand, ligands represented by General Formulae (L1) to (L7) below can be given.
In General Formulae (L1) to (L7), each of R71 to R109 independently represents hydrogen, a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, a halogen group, a vinyl group, a substituted or unsubstituted haloalkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 6 carbon atoms, or a substituted or unsubstituted alkylthio group having 1 to 6 carbon atoms. In addition, each of A1 to A3 independently represents nitrogen, hydrogen, or carbon bonded to a substituent R. The substituent R represents an alkyl group having 1 to 6 carbon atoms, a halogen group, a haloalkyl group having 1 to 6 carbon atoms, or a phenyl group.
The iridium complex included in the light-emitting element of one embodiment of the present invention is not limited to the iridium complexes represented by General Formulae (G1) to (G4). Examples of the iridium complex included in the light-emitting element of one embodiment of the present invention include organometallic iridium complexes having pyrimidine skeletons, such as tris(4-methyl-6-phenylpyrimidinato)iridium(III) (abbreviation: Ir(mppm)3), tris(4-t-butyl-6-phenylpyrimidinato)iridium(III) (abbreviation: Ir(tBuppm)3), (acetylacetonato)bis(6-methyl-4-phenylpyrimidinato)iridium(III) (abbreviation: Ir(mppm)2(acac)), (acetylacetonato)bis(6-tert-butyl-4-phenylpyrimidinato)iridium(III) (abbreviation: Ir(tBuppm)2(acac)), (acetylacetonato)bis[4-(2-norbornyl)-6-phenylpyrimidinato]iridium(III) (endo-and exo-mixture) (abbreviation: Ir(nbppm)2(acac)), (acetylacetonato)bis[5-methyl-6-(2-methylphenyl)-4-phenylpyrimidinato]iridium(III) (abbreviation: Ir(mpmppm)2(acac)), (acetylacetonato)bis(4,6-diphenylpyrimidinato)iridium(III) (abbreviation: Ir(dppm)2(acac)), bis{4,6-dimethyl-2-[5-(2,6-dimethylphenyl)-3-(3,5-dimethylphenyl)-2-pyrazinyl-κN]phenyl-κC}(2,4-pentanedionato-κ2O,O′)iridium(III) (abbreviation: Ir(dmdppr-dmp)2(acac)), and bis{2-[5-(2,6-dimethylphenyl)-3-(3,5-dimethylphenyl)-2-pyrazinyl-κN]-4,6-dimethylphenyl-κC}(2,2,6,6-tetramethyl-3,5-heptanedionato-κ2O,O′)iridium(III) (abbreviation: Ir(dmdppr-dmp)2(dpm)); organometallic iridium complexes having pyrazine skeletons, such as (acetylacetonato)bis(3,5-dimethyl-2-phenylpyrazinato)iridium(III) (abbreviation: Ir(mppr-Me)2(acac)), (acetylacetonato)bis(5-isopropyl-3-methyl-2-phenylpyrazinato)iridium(III) (abbreviation: Ir(mppr-iPr)2(acac)), (acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium(III) (abbreviation: Ir(tppr)2(acac)), and bis[2-(3,5-diphenyl-2-pyrazinyl-κN)-phenyl-κC](2,2,6,6-tetramethyl-3,5-heptanedionato-κκ2O,O′)iridium(III) (abbreviation: Ir(tppr)2(dpm)); and organometallic iridium complexes having pyridine skeletons, 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), and bis(2-phenylquinolinato-N,C2′)iridium(III) acetylacetonate (abbreviation: Ir(pq)2(acac)).
The above iridium complexes each have an emission peak at greater than or equal to 480 nm and less than or equal to 650 nm. Among the iridium complexes given above, the iridium complex having a pyrimidine skeleton has distinctively high reliability and emission efficiency and is thus especially preferable. By preventing a reduction in purity of the above iridium complex in a light-emitting element, the light-emitting element can have a long lifetime. An increase in purity of the above iridium complex in a light-emitting element greatly contributes to extension of the lifetime of the light-emitting element.
As the electron-transport material used for the light-emitting layer 110, a π-electron deficient heteroaromatic compound such as a nitrogen-containing heteroaromatic compound is preferable. As the electron-transport material, a π-electron deficient heteroaromatic compound, a metal complex, or the like can be used. Specific examples include 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); a heterocyclic 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), or 2-[3-(dibenzothiophen-4-yl)phenyl]-1-phenyl-1H-benzimidazole (abbreviation: mDBTBIm-II); a heterocyclic compound having a diazine skeleton such as 2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTPDBq-II), 2-[3′-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f h]quinoxaline (abbreviation: 2mDBTBPDBq-II), 2-[3′-(9H-carbazol-9-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline (abbreviation: 2mCzBPDBq), 4,6-bis[3-(phenanthren-9-yl)phenyl]pyrimidine (abbreviation: 4,6mPnP2Pm), or 4,6-bis[3-(4-dibenzothienyl)phenyl]pyrimidine (abbreviation: 4,6mDBTP2Pm-II); a heterocyclic compound having a triazine skeleton such as 2-{4-[3-(N-phenyl-9H-carbazol-3-yl)-9H-carbazol-9-yl]phenyl}-4,6-diphenyl-1,3,5-triazine (abbreviation: PCCzPTzn); and a heterocyclic compound having a pyridine skeleton such as 3,5-bis[3-(9H-carbazol-9-yl)phenyl]pyridine (abbreviation: 35DCzPPy) or 1,3,5-tri[3-(3-pyridyl)phenyl]benzene (abbreviation: TmPyPB). Among the above materials, a heterocyclic compound having a diazine skeleton, a heterocyclic compound having a triazine skeleton, and a heterocyclic compound having a pyridine skeleton have high reliability and are thus preferable. Heterocyclic compounds having diazine (pyrimidine or pyrazine) skeletons and triazine skeletons have a high electron-transport property and contribute to a decrease in drive voltage.
As the hole-transport material used for the light-emitting layer 110, a π-electron rich heteroaromatic compound or an aromatic amine compound is preferable. As the hole-transport material, a π-electron rich heteroaromatic compound, an aromatic amine compound, or the like can be favorably used. Specific examples include a compound having an aromatic amine skeleton such as 2-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]spiro-9,9′-bifluorene (abbreviation: PCASF), 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB), N,N′-bis(3-methylphenyl)-N,N-diphenyl-[1,1′-biphenyl]-4,4′-diamine (abbreviation: TPD), 4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl (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: PCBAlBP), 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), 9,9-dimethyl-N-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]fluoren-2-amine (abbreviation: PCBAF), N-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]spiro-9,9′-bifluoren-2-amine (abbreviation: PCBASF), N-(1,1′-biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H-fluoren-2-amine (abbreviation: PCBBiF); a compound 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), or 9-phenyl-9H-3-(9-phenyl-9H-carbazol-3-yl)carbazole (abbreviation: PCCP); a compound 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), or 4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-6-phenyldibenzothiophene (abbreviation: DBTFLP-IV); and a compound having a furan skeleton such as 4,4′,4″-(benzene-1,3,5-triyl)tri(dibenzofuran) (abbreviation: DBF3P-II) or 4-{3-[3-(9-phenyl-9H-fluoren-9-yl)phenyl]phenyl}dibenzofuran (abbreviation: mmDBFFLBi-II). Among the above materials, a compound having an aromatic amine skeleton and a 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 drive voltage.
Furthermore, as the hole-transport material used for the light-emitting layer 110, a high molecular compound such as poly(N-vinylcarbazole) (abbreviation: PVK), poly(4-vinyltriphenylamine) (abbreviation: PVTPA), poly[N-(4-{N′-[4-(4-diphenylamino)phenyl]phenyl-N′-phenylamino}phenyl)methacrylamide] (abbreviation: PTPDMA), or poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine] (abbreviation: Poly-TPD) can be used.
The electron-transport material and the hole-transport material used for the light-emitting layer 110 preferably form an exciplex (also called excited complex). For example, the electron-transport material and the hole-transport material used for the light-emitting layer 110 accept electrons and holes, respectively. At this time, the electron-transport material and the hole-transport material come close to each other, thereby forming an exciplex immediately. Therefore, most excitons in the light-emitting layer 110 exist as the exciplexes. The band gap of the exciplex is smaller than that of the electron-transport material and that of the hole-transport material, which allows the drive voltage of the light-emitting element 100 to be reduced.
It is preferable that energy be transferred from the exciplex to the iridium complex included in the light-emitting element of one embodiment of the present invention. Specifically, light emission is preferably achieved by transfer of both energy of the lowest level (SE) of a singlet excited state of the exciplex and energy of the lowest level (TE) of a triplet excited state of the exciplex to the lowest level of a triplet excited state of the iridium complex, in which case high emission efficiency can be achieved.
The hole-injection layer 131 is a layer that injects holes into the light-emitting layer 110 through the hole-transport layer 132 with a high hole-transport property and includes a hole-transport material and an acceptor substance. When a hole-transport material and an acceptor substance are included, electrons are extracted from the hole-transport material by the acceptor substance to generate holes, and the holes are injected into the light-emitting layer 110 through the hole-transport layer 132. Note that the hole-transport layer 132 is formed using a hole-transport material.
As a hole-transport material used for the hole-injection layer 131 and the hole-transport layer 132, a material similar to the aforementioned hole-transport material that can be used for the light-emitting layer 110 is used.
Examples of the acceptor substance that is used for the hole-injection layer 131 include oxides of metals belonging to Groups 4 to 8 of the periodic table. Specifically, it is particularly preferable to use molybdenum oxide.
For the electron-transport layer 133, a material similar to the aforementioned electron-transport material that can be used for the light-emitting layer 110 is used. Note that in the light-emitting element 100 shown in
The electron-injection layer 134 is a layer including a substance with a high electron-injection property. For the electron-injection layer 134, an alkali metal, an alkaline earth metal, or a compound thereof, such as lithium fluoride (LiF), cesium fluoride (CsF), calcium fluoride (CaF2), or lithium oxide (LiOx), can be used. Alternatively, a rare earth metal compound such as erbium fluoride (ErF3) can be used. Electride may also be used for the electron-injection layer 134. Examples of the electride include a substance in which electrons are added at high concentration to calcium oxide-aluminum oxide.
Alternatively, the electron-injection layer 134 may be formed using a composite material in which an organic compound and an electron donor (donor) are mixed. The composite material is superior in an electron-injection property and an electron-transport property, since electrons are generated in the organic compound by the electron donor. The organic compound here is preferably a material excellent in transporting the generated electrons; specifically, for example, the substances for forming the electron-transport layer 133 (e.g., a metal complex or a heteroaromatic compound) can be used. As the electron donor, a substance showing an electron-donating property with respect to the organic compound may be used. Specifically, an alkali metal, an alkaline earth metal, and a rare earth metal are preferable, and lithium, cesium, magnesium, calcium, erbium, ytterbium, and the like are given. Furthermore, an alkali metal oxide or an alkaline earth metal oxide is preferable, and for example, lithium oxide, calcium oxide, barium oxide, and the like can be given. Alternatively, Lewis base such as magnesium oxide can also be used. An organic compound such as tetrathiafulvalene (abbreviation: TTF) can also be used.
The structure described in this embodiment can be used in appropriate combination with any of the structures described in other embodiments or examples.
In this embodiment, a light-emitting element of one embodiment of the present invention is described with reference to
The light-emitting element 150 includes a plurality of light-emitting units (a first light-emitting unit 141 and a second light-emitting unit 142 in
In the light-emitting element 150 shown in
The charge generation layer 143 includes a composite material of an organic compound and a metal oxide. For the composite material, the composite material that can be used for the hole-injection layer 111 described above may be used. As the organic compound, a variety of compounds such as an aromatic amine compound, a carbazole compound, an aromatic hydrocarbon, and a high molecular compound (such as an oligomer, a dendrimer, or a polymer) can be used. An organic compound having a hole mobility of 1×10−6 cm2/Vs or higher is preferably used. Note that any other substance may be used as long as the substance has a hole-transport property higher than an electron-transport property. Since the composite material of an organic compound and a metal oxide is superior in carrier-injecting property and carrier-transporting property, low-voltage driving or low-current driving can be realized. Note that when a surface of a light-emitting unit on the anode side is in contact with the charge generation layer 143, the charge generation layer 143 can also serve as a hole-transport layer of the light-emitting unit; thus, a hole-transport layer does not need to be formed in the light-emitting unit.
The charge generation layer 143 may have a stacked-layer structure of a layer containing the composite material of an organic compound and a metal oxide and a layer containing another material. For example, the charge generation layer 143 may be formed using a combination of a layer containing the composite material of an organic compound and a metal oxide with a layer containing one compound selected from among electron-donating substances and a compound having a high electron-transporting property. Further, the charge generation layer 143 may be formed using a combination of a layer containing the composite material of an organic compound and a metal oxide with a transparent conductive film.
In any case, as the charge-generation layer 143, which is provided between the first light-emitting unit 141 and the second light-emitting unit 142, acceptable is a layer which injects electrons into the light-emitting unit on one side and injects holes into the light-emitting unit on the other side when voltage is applied to the lower electrode 104 and the upper electrode 114. For example, in
In
When the EL layer 108 or the light-emitting layer 110 described in Embodiment 1 is included in at least one of the plurality of units, a highly reliable light-emitting element can be provided.
Any one of the first light-emitting unit 141 and the second light-emitting unit 142 may include a fluorescent material as a light-emitting substance. For example, the light-emitting layer in any one of the first light-emitting unit 141 and the second light-emitting unit 142 includes a host material and a fluorescent material.
In the light-emitting layer of any one of the first light-emitting unit 141 and the second light-emitting unit 142, the host material is present in the highest proportion by weight, and the fluorescent material is dispersed in the host material. It is preferable that the S1 level of the host material be higher than the S1 level of the fluorescent material, and the T1 level of the host material be lower than the T1 level of the fluorescent material.
An anthracene derivative or a tetracene derivative is preferably used as the host material. This is because these derivatives each have a high S1 level and a low T1 level. Specific examples 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), and 9-phenyl-10-{4-(9-phenyl-9H-fluoren-9-yl)biphenyl-4′-yl}anthracene (abbreviation: FLPPA). Besides, 5,12-diphenyltetracene, 5,12-bis(biphenyl-2-yl)tetracene, and the like can be given.
Examples of the fluorescent material include a pyrene derivative, an anthracene derivative, a triphenylene derivative, a fluorene derivative, a carbazole derivative, a dibenzothiophene derivative, a dibenzofuran derivative, a dibenzoquinoxaline derivative, a quinoxaline derivative, a pyridine derivative, a pyrimidine derivative, a phenanthrene derivative, and a naphthalene derivative. A pyrene derivative is particularly preferable because it has a high emission quantum yield. Specific examples of the pyrene derivative include 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-(9-phenyl-9H-fluoren-9-yl)phenyl]-N,N′-diphenylpyrene-1,6-diamine (abbreviation: 1,6FLPAPrn), N,N′-bis(dibenzofuran-2-yl)-N,N′-diphenylpyrene-1,6-diamine (abbreviation: 1,6FrAPrn), and N,N′-bis(dibenzothiophen-2-yl)-N,N′-diphenylpyrene-1,6-diamine (abbreviation: 1,6ThAPrn).
The above-described structure can be combined with any of the structures in this embodiment and other embodiments.
In this embodiment, a display device including a light-emitting device of one embodiment of the present invention will be described with reference to
The display device illustrated in
A part or the whole of the driver circuit portion 804 is preferably formed over a substrate over which the pixel portion 802 is formed, in which case the number of components and the number of terminals can be reduced. When a part or the whole of the driver circuit portion 804 is not formed over the substrate over which the pixel portion 802 is formed, the part or the whole of the driver circuit portion 804 can be mounted by COG or tape automated bonding (TAB).
The pixel portion 802 includes a plurality of circuits for driving display elements arranged in X rows (X is a natural number of 2 or more) and Y columns (Y is a natural number of 2 or more) (such circuits are hereinafter referred to as pixel circuits 801). The driver circuit portion 804 includes driver circuits such as a circuit for supplying a signal (scan signal) to select a pixel (the circuit is hereinafter referred to as a gate driver 804a) and a circuit for supplying a signal (data signal) to drive a display element in a pixel (the circuit is hereinafter referred to as a source driver 804b).
The gate driver 804a includes a shift register or the like. Through the terminal portion 807, the gate driver 804a receives a signal for driving the shift register and outputs a signal. For example, the gate driver 804a receives a start pulse signal, a clock signal, or the like and outputs a pulse signal. The gate driver 804a has a function of controlling the potentials of wirings supplied with scan signals (such wirings are hereinafter referred to as scan lines GL_1 to GL_X). Note that a plurality of gate drivers 804a may be provided to control the scan lines GL_1 to GL_X separately. Alternatively, the gate driver 804a has a function of supplying an initialization signal. Without being limited thereto, the gate driver 804a can supply another signal.
The source driver 804b includes a shift register or the like. The source driver 804b receives a signal (video signal) from which a data signal is derived, as well as a signal for driving the shift register, through the terminal portion 807. The source driver 804b has a function of generating a data signal to be written to the pixel circuit 801 which is based on the video signal. In addition, the source driver 804b has a function of controlling output of a data signal in response to a pulse signal produced by input of a start pulse signal, a clock signal, or the like. Furthermore, the source driver 804b has a function of controlling the potentials of wirings supplied with data signals (such wirings are hereinafter referred to as data lines DL_1 to DL_Y). Alternatively, the source driver 804b has a function of supplying an initialization signal. Without being limited thereto, the source driver 804b can supply another signal.
The source driver 804b includes a plurality of analog switches or the like, for example. The source driver 804b can output, as the data signals, signals obtained by time-dividing the video signal by sequentially turning on the plurality of analog switches. The source driver 804b may include a shift register or the like.
A pulse signal and a data signal are input to each of the plurality of pixel circuits 801 through one of the plurality of scan lines GL supplied with scan signals and one of the plurality of data lines DL supplied with data signals, respectively. Writing and holding of the data signal to and in each of the plurality of pixel circuits 801 are controlled by the gate driver 804a. For example, to the pixel circuit 801 in the m-th row and the n-th column (in is a natural number of less than or equal to X, and n is a natural number of less than or equal to Y), a pulse signal is input from the gate driver 804a through the scan line GL_m, and a data signal is input from the source driver 804b through the data line DL_n in accordance with the potential of the scan line GL_m.
The protection circuit 806 shown in
The protection circuit 806 is a circuit that electrically connects a wiring connected to the protection circuit to another wiring when a potential out of a certain range is applied to the wiring connected to the protection circuit.
As illustrated in
In
Each of the plurality of pixel circuits 801 in
The pixel circuit 801 illustrated in
One of a source electrode and a drain electrode of the transistor 852 is electrically connected to a wiring to which a data signal is supplied (hereinafter referred to as a signal line DL_n). A gate electrode of the transistor 852 is electrically connected to a wiring to which a gate signal is supplied (hereinafter referred to as a scan line GL_m).
The transistor 852 has a function of controlling whether to write a data signal by being turned on or off.
One of a pair of electrodes of the capacitor 862 is electrically connected to a wiring to which a potential is supplied (hereinafter referred to as a potential supply line VL_a), and the other is electrically connected to the other of the source electrode and the drain electrode of the transistor 852.
The capacitor 862 functions as a storage capacitor for storing written data.
One of a source electrode and a drain electrode of the transistor 854 is electrically connected to the potential supply line VL_a. Furthermore, a gate electrode of the transistor 854 is electrically connected to the other of the source electrode and the drain electrode of the transistor 852.
One of an anode and a cathode of the light-emitting element 872 is electrically connected to a potential supply line VL_b, and the other is electrically connected to the other of the source electrode and the drain electrode of the transistor 854.
As the light-emitting element 872, the light-emitting element 100 described in Embodiment 1 can be used.
Note that a high power supply potential VDD is supplied to one of the potential supply line VL_a and the potential supply line VL_b, and a low power supply potential VSS is supplied to the other.
In the display device including the pixel circuits 801 in
When the transistors 852 are turned off, the pixel circuits 801 in which the data has been written are brought into a holding state. Furthermore, the amount of current flowing between the source electrode and the drain electrode of the transistor 854 is controlled in accordance with the potential of the written data signal. The light-emitting element 872 emits light with a luminance corresponding to the amount of flowing current. This operation is sequentially performed row by row; thus, an image is displayed.
Alternatively, the pixel circuit can have a function of compensating variation in threshold voltages or the like of a transistor.
The pixel circuit illustrated in
The pixel circuit shown in
The pixel circuit shown in
The pixel circuit illustrated in
A light-emitting element of one embodiment of the present invention can be used for an active matrix method in which an active element is included in a pixel of a display device or a passive matrix method in which an active element is not included in a pixel of a display device.
In the active matrix method, as an active element (a non-linear element), not only a transistor but also a variety of active elements (non-linear elements) can be used. For example, a metal insulator metal (MIM), a thin film diode (TFD), or the like can also be used. Since these elements can be formed with a smaller number of manufacturing steps, manufacturing cost can be reduced or yield can be improved. Alternatively, since the size of these elements is small, the aperture ratio can be improved, so that power consumption can be reduced or higher luminance can be achieved.
As a method other than the active matrix method, the passive matrix method in which an active element (a non-linear element) is not used can also be used. Since an active element (a non-linear element) is not used, the number of manufacturing steps is small, so that manufacturing cost can be reduced or yield can be improved. Alternatively, since an active element (a non-linear element) is not used, the aperture ratio can be improved, so that power consumption can be reduced or higher luminance can be achieved, for example.
The structure described in this embodiment can be combined with any of the structures described in the other embodiments as appropriate.
In this embodiment, a display panel including a light-emitting device of one embodiment of the present invention and an electronic device in which the display panel is provided with an input device will be described with reference to
In this embodiment, a touch panel 2000 including a display panel and an input device will be described as an example of an electronic device. In addition, an example in which a touch sensor is used as an input device will be described. Note that a light-emitting device of one embodiment of the present invention can be used for a pixel of the display panel.
The touch panel 2000 includes a display panel 2501 and a touch sensor 2595 (see
The display panel 2501 includes a plurality of pixels over the substrate 2510 and a plurality of wirings 2511 through which signals are supplied to the pixels. The plurality of wirings 2511 are led to a peripheral portion of the substrate 2510, and parts of the plurality of wirings 2511 form a terminal 2519. The terminal 2519 is electrically connected to an FPC 2509(1).
The substrate 2590 includes the touch sensor 2595 and a plurality of wirings 2598 electrically connected to the touch sensor 2595. The plurality of wirings 2598 are led to a peripheral portion of the substrate 2590, and parts of the plurality of wirings 2598 form a terminal. The terminal is electrically connected to an FPC 2509(2). Note that in
As the touch sensor 2595, a capacitive touch sensor can be used. Examples of the capacitive touch sensor are a surface capacitive touch sensor and a projected capacitive touch sensor.
Examples of the projected capacitive touch sensor are a self-capacitive touch sensor and a mutual capacitive touch sensor, which differ mainly in the driving method. The use of a mutual capacitive touch sensor is preferable because multiple points can be sensed simultaneously.
Note that the touch sensor 2595 illustrated in
Note that a variety of sensors that can sense proximity or touch of a sensing target such as a finger can be used as the touch sensor 2595.
The projected capacitive touch sensor 2595 includes electrodes 2591 and electrodes 2592. The electrodes 2591 are electrically connected to any of the plurality of wirings 2598, and the electrodes 2592 are electrically connected to any of the other wirings 2598.
The electrodes 2592 each have a shape of a plurality of quadrangles arranged in one direction with one corner of a quadrangle connected to one corner of another quadrangle as illustrated in
The electrodes 2591 each have a quadrangular shape and are arranged in a direction intersecting with the direction in which the electrodes 2592 extend.
A wiring 2594 electrically connects two electrodes 2591 between which the electrode 2592 is positioned. The intersecting area of the electrode 2592 and the wiring 2594 is preferably as small as possible. Such a structure allows a reduction in the area of a region where the electrodes are not provided, reducing variation in transmittance. As a result, variation in luminance of light passing through the touch sensor 2595 can be reduced.
Note that the shapes of the electrodes 2591 and the electrodes 2592 are not limited thereto and can be any of a variety of shapes. For example, a structure may be employed in which the plurality of electrodes 2591 are arranged so that gaps between the electrodes 2591 are reduced as much as possible, and the electrodes 2592 are spaced apart from the electrodes 2591 with an insulating layer interposed therebetween to have regions not overlapping with the electrodes 2591. In this case, it is preferable to provide, between two adjacent electrodes 2592, a dummy electrode electrically insulated from these electrodes because the area of regions having different transmittances can be reduced.
Note that for example, a transparent conductive film including indium oxide, tin oxide, zinc oxide, or the like (e.g., a film of ITO) can be given as a material of conductive films used for the electrode 2591, the electrode 2592, and the wiring 2598, i.e., wirings and electrodes in the touch panel. Moreover, for example, a low-resistance material is preferably used as the material of the wiring and the electrode in the touch panel. For example, silver, copper, aluminum, a carbon nanotube, graphene, or a metal halide (such as a silver halide) may be used. Alternatively, a metal nanowire including a plurality of conductors with an extremely small width (e.g., a diameter of several nanometers) may be used. Further alternatively, a net-like metal mesh with a conductor may be used. Examples of such materials include an Ag nanowire, a Cu nanowire, an Al nanowire, an Ag mesh, a Cu mesh, and an Al mesh. For example, in the case of using an Ag nanowire for the wiring and the electrode in the touch panel, a visible light transmittance of 89% or more and a sheet resistance of 40 Ω/cm2 or more and 100 Ω/cm2 or less can be achieved. A metal nanowire, a metal mesh, a carbon nanotube, graphene, and the like, which are examples of a material that can be used for the above-described wiring and electrode in the touch panel, have a high visible light transmittance; therefore, they may be used for an electrode of a display element (e.g., a pixel electrode or a common electrode).
Next, the display panel 2501 will be described in detail with reference to
The display panel 2501 includes a plurality of pixels arranged in a matrix. Each of the pixels includes a display element and a pixel circuit for driving the display element.
For the substrate 2510 and the substrate 2570, for example, a flexible material with a vapor permeability of lower than or equal to 10−5 g/(m2·day), preferably lower than or equal to 10−6 g/(m2·day) can be favorably used. Alternatively, materials whose thermal expansion coefficients are substantially equal to each other are preferably used for the substrate 2510 and the substrate 2570. For example, the coefficients of linear expansion of the materials are preferably lower than or equal to 1×10−3/K, further preferably lower than or equal to 5×10−5/K, and still further preferably lower than or equal to 1×10−5/K.
Note that the substrate 2510 is a stacked body including an insulating layer 2510a for preventing impurity diffusion into the light-emitting element, a flexible substrate 2510b, and an adhesive layer 2510c for attaching the insulating layer 2510a and the flexible substrate 2510b to each other. The substrate 2570 is a stacked body including an insulating layer 2570a for preventing impurity diffusion into the light-emitting element, a flexible substrate 2570b, and an adhesive layer 2570c for attaching the insulating layer 2570a and the flexible substrate 2570b to each other.
For the adhesive layer 2510c and the adhesive layer 2570c, for example, materials that include polyester, polyolefin, polyamide (e.g., nylon, aramid), polyimide, polycarbonate, polyurethane, an acrylic resin, an epoxy resin, or a resin having a siloxane bond can be used.
A sealing layer 2560 is provided between the substrate 2510 and the substrate 2570. The sealing layer 2560 preferably has a refractive index higher than that of air. In the case where light is extracted to the sealing layer 2560 side as illustrated in
A sealant may be formed in the peripheral portion of the sealing layer 2560. With the use of the sealant, a light-emitting element 2550R can be provided in a region surrounded by the substrate 2510, the substrate 2570, the sealing layer 2560, and the sealant. Note that an inert gas (such as nitrogen or argon) may be used instead of the sealing layer 2560. A drying agent may be provided in the inert gas so as to adsorb moisture or the like. For example, an epoxy-based resin or a glass frit is preferably used as the sealant. As a material used for the sealant, a material which is impermeable to moisture or oxygen is preferably used.
The display panel 2501 includes a pixel 2502. The pixel 2502 includes a light-emitting module 2580.
The pixel 2502 includes the light-emitting element 2550R and a transistor 2502t that can supply electric power to the light-emitting element 2550R. Note that the transistor 2502t functions as part of the pixel circuit. The light-emitting module 2580 includes the light-emitting element 2550R and a coloring layer 2567R.
The light-emitting element 2550 includes a lower electrode, an upper electrode, and an EL layer between the lower electrode and the upper electrode. As the light-emitting element 2550, the light-emitting element 100 described in Embodiment 1 can be used, for example. Note that although only one light-emitting element 2550 is illustrated in
In the case where the sealing layer 2560 is provided on the light extraction side, the sealing layer 2560 is in contact with the light-emitting element 2550 and the coloring layer 2567R.
The coloring layer 2567R is positioned in a region overlapping with the light-emitting element 2550. Accordingly, part of light emitted from the light-emitting element 2550 passes through the coloring layer 2567R and is emitted to the outside of the light-emitting module 2580 as indicated by an arrow in
The display panel 2501 includes a light-blocking layer 2567BM on the light extraction side. The light-blocking layer 2567BM is provided so as to surround the coloring layer 2567R.
The coloring layer 2567R is a coloring layer having a function of transmitting light in a particular wavelength region. For example, a color filter for transmitting light in a red wavelength range, a color filter for transmitting light in a green wavelength range, a color filter for transmitting light in a blue wavelength range, a color filter for transmitting light in a yellow wavelength range, or the like can be used. Each color filter can be formed with any of various materials by a printing method, an inkjet method, an etching method using a photolithography technique, or the like.
An insulating layer 2521 is provided in the display panel 2501. The insulating layer 2521 covers the transistor 2502t. Note that the insulating layer 2521 has a function of covering unevenness caused by the pixel circuit to provide a flat surface. The insulating layer 2521 may have a function of suppressing impurity diffusion. This can prevent the reliability of the transistor 2502t or the like from being lowered by impurity diffusion.
The light-emitting element 2550R is formed over the insulating layer 2521. A partition 2528 is provided so as to overlap with an end portion of the lower electrode of the light-emitting element 2550R. Note that a spacer for controlling the distance between the substrate 2510 and the substrate 2570 may be formed over the partition 2528.
A scan line driver circuit 2503g includes a transistor 2503t and a capacitor 2503c. Note that the driver circuit can be formed in the same process and over the same substrate as those of the pixel circuits.
The wirings 2511 through which signals can be supplied are provided over the substrate 2510. The terminal 2519 is provided over the wirings 2511. The FPC 2509(1) is electrically connected to the terminal 2519. The FPC 2509(1) has a function of supplying a video signal, a clock signal, a start signal, a reset signal, or the like. Note that the FPC 2509(1) may be provided with a PWB.
In the display panel 2501, transistors with any of a variety of structures can be used.
In addition, there is no particular limitation on the polarity of the transistor 2502t and the transistor 2503t. For these transistors, n-channel and p-channel transistors may be used, or either n-channel transistors or p-channel transistors may be used, for example. Furthermore, there is no particular limitation on the crystallinity of a semiconductor film used for the transistors 2502t and 2503t. For example, an amorphous semiconductor film or a crystalline semiconductor film may be used. Examples of semiconductor materials include Group 13 semiconductors (e.g., a semiconductor including gallium), Group 14 semiconductors (e.g., a semiconductor including silicon), compound semiconductors (including oxide semiconductors), organic semiconductors, and the like. An oxide semiconductor that has an energy gap of 2 eV or more, preferably 2.5 eV or more, further preferably 3 eV or more is preferably used for one of the transistors 2502t and 2503t or both, so that the off-state current of the transistors can be reduced. Examples of the oxide semiconductors include an In—Ga oxide, an In-M-Zn oxide (M represents Al, Ga, Y, Zr, La, Ce, Sn, or Nd), and the like.
Next, the touch sensor 2595 will be described in detail with reference to
The touch sensor 2595 includes the electrodes 2591 and the electrodes 2592 provided in a staggered arrangement on the substrate 2590, an insulating layer 2593 covering the electrodes 2591 and the electrodes 2592, and the wiring 2594 that electrically connects the adjacent electrodes 2591 to each other.
The electrodes 2591 and the electrodes 2592 are formed using a light-transmitting conductive material. As a light-transmitting conductive material, a conductive oxide such as indium oxide, indium tin oxide, indium zinc oxide, zinc oxide, or zinc oxide to which gallium is added can be used. Note that a film including graphene may be used as well. The film including graphene can be formed, for example, by reducing a film containing graphene oxide. As a reducing method, a method with application of heat or the like can be employed.
The electrodes 2591 and the electrodes 2592 may be formed by, for example, depositing a light-transmitting conductive material on the substrate 2590 by a sputtering method and then removing an unnecessary portion by any of various patterning techniques such as photolithography.
Examples of a material for the insulating layer 2593 are a resin such as an acrylic resin or an epoxy resin, a resin having a siloxane bond, and an inorganic insulating material such as silicon oxide, silicon oxynitride, or aluminum oxide.
Openings reaching the electrodes 2591 are formed in the insulating layer 2593, and the wiring 2594 electrically connects the adjacent electrodes 2591. A light-transmitting conductive material can be favorably used as the wiring 2594 because the aperture ratio of the touch panel can be increased. Moreover, a material with conductivity higher than the conductivities of the electrodes 2591 and 2592 can be favorably used for the wiring 2594 because electric resistance can be reduced.
One electrode 2592 extends in one direction, and the plurality of electrodes 2592 are provided in the form of stripes. The wiring 2594 intersects with the electrode 2592.
Adjacent electrodes 2591 are provided with one electrode 2592 provided therebetween. The wiring 2594 electrically connects the adjacent electrodes 2591.
Note that the plurality of electrodes 2591 are not necessarily arranged in the direction orthogonal to one electrode 2592 and may be arranged to intersect with one electrode 2592 at an angle of more than 0 degrees and less than 90 degrees.
The wiring 2598 is electrically connected to any of the electrodes 2591 and 2592. Part of the wiring 2598 functions as a terminal. For the wiring 2598, a metal material such as aluminum, gold, platinum, silver, nickel, titanium, tungsten, chromium, molybdenum, iron, cobalt, copper, or palladium or an alloy material containing any of these metal materials can be used.
Note that an insulating layer that covers the insulating layer 2593 and the wiring 2594 may be provided to protect the touch sensor 2595.
A connection layer 2599 electrically connects the wiring 2598 to the FPC 2509(2).
As the connection layer 2599, any of various anisotropic conductive films (ACF), anisotropic conductive pastes (ACP), or the like can be used.
Next, the touch panel 2000 will be described in detail with reference to
In the touch panel 2000 illustrated in
The touch panel 2000 illustrated in
The adhesive layer 2597 is provided in contact with the wiring 2594. Note that the adhesive layer 2597 attaches the substrate 2590 to the substrate 2570 so that the touch sensor 2595 overlaps with the display panel 2501. The adhesive layer 2597 preferably has a light-transmitting property. A heat curable resin or an ultraviolet curable resin can be used for the adhesive layer 2597. For example, an acrylic resin, a urethane-based resin, an epoxy-based resin, or a siloxane-based resin can be used.
The anti-reflective layer 2567p is positioned in a region overlapping with pixels. As the anti-reflective layer 2567p, a circularly polarizing plate can be used, for example.
Next, a touch panel having a structure different from that illustrated in
The coloring layer 2567R is positioned in a region overlapping with the light-emitting element 2550R. The light-emitting element 2550R illustrated in
The touch sensor 2595 is provided on the substrate 2510 side of the display panel 2501.
The adhesive layer 2597 is provided between the substrate 2510 and the substrate 2590 and attaches the touch sensor 2595 to the display panel 2501.
As illustrated in
Next, an example of a method for driving a touch panel will be described with reference to
The pulse voltage output circuit 2601 is a circuit for sequentially applying a pulse voltage to the wirings X1 to X6. By application of a pulse voltage to the wirings X1 to X6, an electric field is generated between the electrodes 2621 and 2622 of the capacitor 2603. When the electric field between the electrodes is shielded, for example, a change occurs in the capacitor 2603 (mutual capacitance). The approach or contact of a sensing target can be sensed by utilizing this change.
The current sensing circuit 2602 is a circuit for detecting changes in current flowing through the wirings Y1 to Y6 that are caused by the change in mutual capacitance in the capacitor 2603. No change in current value is detected in the wirings Y1 to Y6 when there is no approach or contact of a sensing target, whereas a decrease in current value is detected when mutual capacitance is decreased owing to the approach or contact of a sensing target. Note that an integrator circuit or the like is used for sensing of current values.
A pulse voltage is sequentially applied to the wirings X1 to X6, and the waveforms of the wirings Y1 to Y6 change in accordance with the pulse voltage. When there is no approach or contact of a sensing target, the waveforms of the wirings Y1 to Y6 change in accordance with changes in the voltages of the wirings X1 to X6. The current value is decreased at the point of approach or contact of a sensing target and accordingly the waveform of the voltage value changes.
By detecting a change in mutual capacitance in this manner, the approach or contact of a sensing target can be sensed.
Although
The sensor circuit in
A signal G2 is input to a gate of the transistor 2613. A voltage VRES is applied to one of a source and a drain of the transistor 2613, and one electrode of the capacitor 2603 and a gate of the transistor 2611 are electrically connected to the other of the source and the drain of the transistor 2613. One of a source and a drain of the transistor 2611 is electrically connected to one of a source and a drain of the transistor 2612, and a voltage VSS is applied to the other of the source and the drain of the transistor 2611. A signal G1 is input to a gate of the transistor 2612, and a wiring ML is electrically connected to the other of the source and the drain of the transistor 2612. The voltage VSS is applied to the other electrode of the capacitor 2603.
Next, the operation of the sensor circuit in
Then, mutual capacitance of the capacitor 2603 changes owing to the approach or contact of a sensing target such as a finger, and accordingly the potential of the node n is changed from VRES.
In reading operation, a potential for turning on the transistor 2612 is supplied as the signal G1. A current flowing through the transistor 2611, that is, a current flowing through the wiring ML is changed in accordance with the potential of the node n. By sensing this current, the approach or contact of a sensing target can be sensed.
In each of the transistors 2611, 2612, and 2613, an oxide semiconductor layer is preferably used as a semiconductor layer in which a channel region is formed. In particular, such a transistor is preferably used as the transistor 2613 so that the potential of the node n can be held for a long time and the frequency of operation of resupplying VRES to the node n (refresh operation) can be reduced.
The structure described in this embodiment can be combined with any of the structures described in the other embodiments as appropriate.
In this embodiment, a display module and electronic devices including a light-emitting device of one embodiment of the present invention will be described with reference to
In a display module 8000 in
The light-emitting device of one embodiment of the present invention can be used for the display panel 8006, for example.
The shapes and sizes of the upper cover 8001 and the lower cover 8002 can be changed as appropriate in accordance with the sizes of the touch sensor 8004 and the display panel 8006.
The touch sensor 8004 can be a resistive touch panel or a capacitive touch panel and may be formed to overlap with the display panel 8006. A counter substrate (sealing substrate) of the display panel 8006 can have a touch sensor function. A photosensor may be provided in each pixel of the display panel 8006 so that an optical touch sensor is obtained.
The frame 8009 protects the display panel 8006 and also serves as an electromagnetic shield for blocking electromagnetic waves generated by the operation of the printed circuit board 8010. The frame 8009 may serve as a radiator plate.
The printed circuit board 8010 has a power supply circuit and a signal processing circuit for outputting a video signal and a clock signal. As a power source for supplying power to the power supply circuit, an external commercial power source or the battery 8011 provided separately may be used. The battery 8011 can be omitted in the case of using a commercial power source.
The display module 8000 can be additionally provided with a member such as a polarizing plate, a retardation plate, or a prism sheet.
The electronic devices illustrated in
The electronic devices illustrated in
The electronic devices described in this embodiment each include the display portion for displaying some sort of data. Note that the light-emitting device of one embodiment of the present invention can also be used for an electronic device which does not have a display portion. The structure in which the display portion of the electronic device described in this embodiment is flexible and display can be performed on the bent display surface or the structure in which the display portion of the electronic device is foldable is described as an example; however, the structure is not limited thereto and a structure in which the display portion of the electronic device is not flexible and display is performed on a plane portion may be employed.
The structure described in this embodiment can be combined with any of the structures described in the other embodiments as appropriate.
In this embodiment, the light-emitting device of one embodiment of the present invention will be described with reference to
The light-emitting device 3000 illustrated in
Light is emitted from the light-emitting element 3005 through one or both of the substrate 3001 and a substrate 3003. In
As illustrated in
Note that in
The substrate 3001 and the substrate 3003 can have structures similar to those of the substrate 102 and the substrate 152 described in Embodiment 1, respectively. The light-emitting element 3005 can have a structure similar to that of the light-emitting elements described in the above embodiments.
For the first sealing region 3007, a material containing glass (e.g., a glass frit, a glass ribbon, and the like) can be used. For the second sealing region 3009, a material containing a resin can be used. With the use of the material containing glass for the first sealing region 3007, productivity and a sealing property can be improved. Moreover, with the use of the material containing a resin for the second sealing region 3009, impact resistance and heat resistance can be improved. However, the materials used for the first sealing region 3007 and the second sealing region 3009 are not limited to such, and the first sealing region 3007 may be formed using the material containing a resin and the second sealing region 3009 may be formed using the material containing glass.
The glass frit may contain, for example, magnesium oxide, calcium oxide, strontium oxide, barium oxide, cesium oxide, sodium oxide, potassium oxide, boron oxide, vanadium oxide, zinc oxide, tellurium oxide, aluminum oxide, silicon dioxide, lead oxide, tin oxide, phosphorus oxide, ruthenium oxide, rhodium oxide, iron oxide, copper oxide, manganese dioxide, molybdenum oxide, niobium oxide, titanium oxide, tungsten oxide, bismuth oxide, zirconium oxide, lithium oxide, antimony oxide, lead borate glass, tin phosphate glass, vanadate glass, or borosilicate glass. The glass frit preferably contains at least one kind of transition metal to absorb infrared light.
As the above glass frits, for example, a fit paste is applied to a substrate and is subjected to heat treatment, laser light irradiation, or the like. The frit paste contains the glass frit and a resin (also referred to as a binder) diluted by an organic solvent. Note that an absorber which absorbs light having the wavelength of laser light may be added to the glass fit. For example, an Nd:YAG laser or a semiconductor laser is preferably used as the laser. The shape of laser light may be circular or quadrangular.
As the above material containing a resin, for example, materials that include polyester, polyolefin, polyamide (e.g., nylon, aramid), polyimide, polycarbonate, polyurethane, an acrylic resin, an epoxy resin, or a resin having a siloxane bond can be used.
Note that in the case where the material containing glass is used for one or both of the first sealing region 3007 and the second sealing region 3009, the material containing glass preferably has a thermal expansion coefficient close to that of the substrate 3001. With the above structure, generation of a crack in the material containing glass or the substrate 3001 due to thermal stress can be suppressed.
For example, the following advantageous effect can be obtained in the case where the material containing glass is used for the first sealing region 3007 and the material containing a resin is used for the second sealing region 3009.
The second sealing region 3009 is provided closer to an outer portion of the light-emitting device 3000 than the first sealing region 3007 is. In the light-emitting device 3000, distortion due to external force or the like increases toward the outer portion. Thus, the outer portion of the light-emitting device 3000 where a larger amount of distortion is generated, that is, the second sealing region 3009 is sealed using the material containing a resin and the first sealing region 3007 provided on an inner side of the second region 3009 is sealed using the material containing glass, whereby the light-emitting device 3000 is less likely to be damaged even when distortion due to external force or the like is generated.
Furthermore, as illustrated in
The first region 3011 and the second region 3013 are preferably filled with, for example, an inert gas such as a rare gas or a nitrogen gas. Note that for the first region 3011 and the second region 3013, a reduced pressure state is preferred to an atmospheric pressure state.
As the desiccant 3018, a substance which adsorbs moisture and the like by chemical adsorption or a substance which adsorbs moisture and the like by physical adsorption can be used. Examples of the substance that can be used as the desiccant 3018 include alkali metal oxides, alkaline earth metal oxide (e.g., calcium oxide, barium oxide, and the like), sulfate, metal halides, perchlorate, zeolite, silica gel, and the like.
Next, modification examples of the light-emitting device 3000 which is illustrated in
In the light-emitting device illustrated in
For the region 3014, for example, materials that include polyester, polyolefin, polyamide (e.g., nylon or aramid), polyimide, polycarbonate, polyurethane, an acrylic resin, an epoxy resin, or a resin having a siloxane bond can be used.
When the above-described material is used for the region 3014, what is called a solid-sealing light-emitting device can be obtained.
In the light-emitting device illustrated in
The substrate 3015 has unevenness as illustrated in
In the light-emitting device illustrated in
The light-emitting device illustrated in
In the light-emitting device illustrated in
The substrate 3016 includes first unevenness positioned closer to the light-emitting element 3005 and second unevenness positioned farther from the light-emitting element 3005. With the structure illustrated in
Thus, the use of the structure described in this embodiment can provide a light-emitting device in which deterioration of a light-emitting element due to impurities such as moisture and oxygen is suppressed. Alternatively, with the structure described in this embodiment, a light-emitting device having high light extraction efficiency can be obtained.
The structure described in this embodiment can be combined with any of the structures described in the other embodiments and examples as appropriate.
In this embodiment, examples in which the light-emitting device of one embodiment of the present invention is applied to various lighting devices and electronic devices will be described with reference to
An electronic device or a lighting device that has a light-emitting region with a curved surface can be obtained with the use of the light-emitting device of one embodiment of the present invention which is manufactured over a substrate having flexibility.
Furthermore, a light-emitting device to which one embodiment of the present invention is applied can also be applied to lighting for motor vehicles, examples of which are lighting for a dashboard, a windshield, a ceiling, and the like.
The lighting 3508 that includes the light-emitting device of one embodiment of the present invention functions as a planar light source. Thus, unlike a point light source typified by an LED, the lighting 3508 can provide light emission with low directivity. When the lighting 3508 and the camera 3506 are used in combination, for example, imaging can be performed by the camera 3506 with the lighting 3508 lighting or flashing. Because the lighting 3508 functions as a planar light source, a photograph as if taken under natural light can be taken.
Note that the multifunction terminal 3500 illustrated in
The housing 3502 can include a speaker, a sensor (a sensor having a function of measuring force, displacement, position, speed, acceleration, angular velocity, rotational frequency, distance, light, liquid, magnetism, temperature, chemical substance, sound, time, hardness, electric field, current, voltage, electric power, radiation, flow rate, humidity, gradient, oscillation, odor, or infrared rays), a microphone, and the like. When a detection device including a sensor for detecting inclination, such as a gyroscope or an acceleration sensor, is provided inside the multifunction terminal 3500, display on the screen of the display portion 3504 can be automatically switched by determining the orientation of the multifunction terminal 3500 (whether the multifunction terminal is placed horizontally or vertically for a landscape mode or a portrait mode).
The display portion 3504 may function as an image sensor. For example, an image of a palm print, a fingerprint, or the like is taken when the display portion 3504 is touched with the palm or the finger, whereby personal authentication can be performed. Furthermore, by providing a backlight or a sensing light source which emits near-infrared light in the display portion 3504, an image of a finger vein, a palm vein, or the like can be taken. Note that the light-emitting device of one embodiment of the present invention may be used for the display portion 3504.
The security light 3600 emits light when the lighting 3608 is gripped or held, for example. An electronic circuit that can control the manner of light emission from the security light 3600 may be provided in the housing 3602. The electronic circuit may be a circuit that enables light emission once or intermittently plural times or may be a circuit that can adjust the amount of emitted light by controlling the current value for light emission. A circuit with which a loud audible alarm is output from the speaker 3610 at the same time as light emission from the lighting 3608 may be incorporated.
The security light 3600 can emit light in various directions; therefore, it is possible to intimidate a thug or the like with light, or light and sound. Moreover, the security light 3600 may include a camera such as a digital still camera to have a photography function.
As described above, lighting devices and electronic devices can be obtained by application of the light-emitting device of one embodiment of the present invention. Note that the light-emitting device can be used for lighting devices and electronic devices in a variety of fields without being limited to the lighting devices and the electronic devices described in this embodiment.
The structure described in this embodiment can be combined with any of the structures described in the other embodiments and examples as appropriate.
In this example, an example of fabricating a light-emitting element of one embodiment of the present invention will be described. Note that in this example, light-emitting elements that were embodiments of the present invention (Light-emitting Element 1 and Light-emitting Element 2) and a comparative light-emitting element (Light-emitting Element 3) were fabricated.
A schematic cross-sectional view of Light-emitting Elements 1 to 3 is shown in
First, over a substrate 502, ITSO was deposited as a lower electrode 504 by a sputtering method. Note that the thickness of the lower electrode 504 was 100 nm and the area of the lower electrode 504 was 4 mm2 (2 mm×2 mm).
Then, for pretreatment before deposition of an organic compound layer by evaporation, the lower electrode 504 side of the substrate 502 provided with the lower electrode 504 was washed with water, baking was performed at 200° C. for 1 hour, and then UV ozone treatment was performed on a surface of the lower electrode 504 for 370 seconds.
After that, the substrate 502 was transferred into a vacuum evaporation apparatus where the pressure had been 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 502 was cooled down for approximately 30 minutes.
Next, the substrate 502 was fixed to a holder provided in the vacuum evaporation apparatus so that a surface of the substrate over which the lower electrode 504 was formed faced downward. In Example 1, by a vacuum evaporation method, a hole-injection layer 531, a hole-transport layer 532, a light-emitting layer 510(1), a light-emitting layer 510(2), an electron-transport layer 533(1), an electron-transport layer 533(2), an electron-injection layer 534, and an upper electrode 514 were sequentially formed. The fabrication method will be described in detail below.
First, after reducing the pressure of the vacuum evaporation apparatus to 10−4 Pa, DBT3P-II and molybdenum oxide were deposited by co-evaporation in a weight ratio of 2:1 (=DBT3P-II: molybdenum oxide), whereby the hole-injection layer 531 was formed over the lower electrode 504. Note that the thickness of the hole-injection layer 531 was 20 nm.
Then, the hole-transport layer 532 was formed over the hole-injection layer 531. As the hole-transport layer 532, BPAFLP was deposited by evaporation. Note that the thickness of the hole-transport layer 532 was 20 nm.
Next, the light-emitting layer 510(1) was formed over the hole-transport layer 532. As the light-emitting layer 510(1), 2mDBTBPDBq-II, N-(1,1′-biphenyl-4-yl)-9,9-dimethyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9H-fluoren-2-amine (abbreviation: PCBBiF), and (acetylacetonato)bis[5-methyl-6-(2-methylphenyl)-4-phenylpyrimidinato]iridium(III) (abbreviation: Ir(mpmppm)2(acac)) were deposited by co-evaporation in a weight ratio of 0.7:0.3:0.05 (=2mDBTBPDBq-II: PCBBiF: Ir(mpmppm)2(acac)). Note that the thickness of the light-emitting layer 510(1) was 20 nm.
Next, the light-emitting layer 510(2) was formed over the light-emitting layer 510(1). As the light-emitting layer 510(2), 2mDBTBPDBq-II, PCBBiF, and Ir(mpmppm)2(acac) were deposited by co-evaporation in a weight ratio of 0.8:0.2:0.05 (=2mDBTBPDBq-II: PCBBiF: Ir(mpmppm)2(acac)). Note that the thickness of the light-emitting layer 510(2) was 20 nm.
In the light-emitting layer 510(1) and the light-emitting layer 510(2), 2mDBTBPDBq-II is a host material, PCBBiF is an assist material, and Ir(mpmppm)2(acac) is an iridium complex serving as a guest material.
Note that the purity of the iridium complex used in the deposition of the light-emitting layers by evaporation was different between Light-emitting Elements 1 to 3. In the deposition of the light-emitting layers by evaporation, the iridium complex that was represented as Material Y1 was used in Light-emitting Element 1; the iridium complex that was represented as Material Y2 was used in Light-emitting Element 2; and the iridium complex that was represented as Material Y3 was used in Light-emitting Element 3. The purity of the iridium complexes that were represented as Materials Y1 to Y3 is shown in Table 5.
Note that the purity of Materials Y1 to Y3 shown in Table 5 was obtained by LC/MS analysis. The LC/MS analysis was performed by a method similar to that described in Embodiment 1, except for the conditions of the LC separation. In the LC separation for Materials Y1 to Y3, a gradient method in which the ratio between mobile phases is changed was employed. The ratio of Mobile Phase A to Mobile Phase B was 60:40 for 0 to 1 minute after the start of the measurement, and then the ratio of Mobile Phase A to Mobile Phase B was changed linearly such that the ratio in the 30th minute was 95:5. That is, the measurement time was 30 minutes.
As a result of the LC/MS analysis, chromatograms of Materials Y1 to Y3 exhibited peaks m1 to m8 shown in Table 5. Note that the peaks m1 to m3 correspond to m/z=811, the peaks m4 and m5 correspond to m/z=797, the peak m6 corresponds to m/z=783, the peak m7 corresponds to m/z=711 and 752, and the peak m8 corresponds to m/z=697 and 738. As a result of analysis using an MS chromatograph, the peak m1 was assigned to Ir(mpmppm)2(acac), and the peaks m2 and m3 were assigned to structural isomers of Ir(mpmppm)2(acac).
As shown in Table 5, the total proportion of peak areas of substances other than the iridium complex to which the peaks m1 to m3 were assigned was 8.7% in Material Y1, 20.8% in Material Y2, and 29% in Material Y3.
After that, over the light-emitting layer 510(2), 2mDBTBPDBq-II was deposited by evaporation to a thickness of 5 nm as the electron-transport layer 533(1). Then, over the electron-transport layer 533(1), Bphen was deposited by evaporation to a thickness of 10 nm as the electron-transport layer 533(2). Then, over the electron-transport layer 533(2), LiF was deposited by evaporation to a thickness of 1 nm as the electron-injection layer 534.
Then, over the electron-injection layer 534, Al was deposited by evaporation to a thickness of 200 nm as the upper electrode 514.
Next, a sealing substrate 552 was prepared.
The light-emitting elements formed over the substrate 502 as described above were sealed by being bonded to the sealing substrate 552 in a glove box in a nitrogen atmosphere so as not to be exposed to the air. For sealing, the sealant was applied to surround the light-emitting element, irradiation with 365-nm ultraviolet light at 6 J/cm2 was performed, and heat treatment was then performed at 80° C. for 1 hour.
Through the above process, Light-emitting Elements 1 to 3 were fabricated.
Note that in all the above evaporation steps for Light-emitting Elements 1 to 3, a resistive heating method was used as an evaporation method.
Next, reliability tests were performed on Light-emitting Elements 1 to 3. In the reliability tests, Light-emitting Elements 1 to 3 were driven under the conditions where the initial luminance was 5000 cd/m2 and the current density was constant.
The results in
The results in
Then, to find out the reason for the difference in reliability between Light-emitting Element 3 that was a comparative light-emitting element and Light-emitting Elements 1 and 2 that were embodiments of the present invention, Light-emitting Elements 1 to 3 were analyzed by LC/MS to examine impurities contained therein.
Note that for analysis of an impurity in Light-emitting Element 1, a light-emitting element that was different from Light-emitting Element 1 and was formed over the same substrate as Light-emitting Element 1 was used; for analysis of an impurity in Light-emitting Element 2, a light-emitting element that was different from Light-emitting Element 2 and was formed over the same substrate as Light-emitting Element 2 was used; for analysis of an impurity in Light-emitting Element 3, a light-emitting element that was different from Light-emitting Element 3 and was formed over the same substrate as Light-emitting Element 3 was used. In each of the light-emitting elements for the impurity analysis, the area of the lower electrode 504 was approximately 12 cm2 (3.5 cm×3.3 cm). In other words, the light-emitting elements for the impurity analysis had the same materials and structures as Light-emitting Elements 1 to 3, but were different from Light-emitting Elements 1 to 3 in the area of the lower electrode 504. The samples for the impurity analysis were not driven; thus, the obtained results were not the analysis results of deteriorated objects produced by driving, but the analysis results of an impurity that had been contained from before driving. Here, the light-emitting element for the impurity analysis that was fabricated over the same substrate as Light-emitting Element 1 is regarded as Light-emitting Element 1 for convenience. The same applies to Light-emitting Elements 2 and 3.
Samples for the LC/MS analysis were obtained in the following manner: aluminum that was the upper electrode 514 of each of Light-emitting Elements 1 to 3 was peeled with the use of a Kapton tape (registered trademark); a substance remaining over the substrate 502 was dissolved in chloroform, so that a chloroform solution was obtained; and the chloroform solution was diluted with acetonitrile to a given concentration. The injection amount of the analysis sample was 5.0 μL in the LC/MS analysis.
The LC/MS analysis was performed by a method similar to that described in Embodiment 1. However, 15 minutes further elapsed after the ratio of Mobile Phase A to Mobile Phase B became 95:5. That is, the measurement time was 30 minutes.
In a manner similar to that of the analysis sample, the chloroform used for fabrication of the samples was diluted with acetonitrile to give a solution, and the solution was analyzed to obtain a base-line (or background: BG) chromatogram. In
As shown in
As can be seen in
Next, the PDA chromatograms were analyzed with a focus on Ir(mpmppm)2(acac). The base line was subtracted in the analysis of the PDA chromatograms.
As shown in
The peaks b7 to b12 were analyzed using an MS chromatograph, which showed that the peak b7 was assigned to a structural isomer (referred to as Structural Isomer 1, for convenience) of Ir(mpmppm)2(acac); the peak b8, a structural isomer (referred to as Structural Isomer 2, for convenience) of Ir(mpmppm)2(acac); the peak b9, a substance with a structure of an mpmppm skeleton (a ligand of Ir(mpmppm)2(acac)) from which one Me group was dissociated; the peak b10, a structural isomer of a structure of an mpmppm skeleton (a ligand of Ir(mpmppm)2(acac)) from which one Me group was dissociated; the peak b11, a substance with a structure of Ir(mpmppm)2, that is, a structure of Ir(mpmppm)2(acac) from which the ligand acac was dissociated; and the peak b12, mpmppm that was a ligand of Ir(mpmppm)2(acac).
In LC/MS analysis, the substance with the structure of Ir(mpmppm)2produced an MS spectrum with a mass-to-charge ratio (m/z) of 753. The mass number of a proton adduct of a structure in which acetonitrile is coordinated to Ir(mpmppm)2 is 753. Thus, it was suggested that acetonitrile was coordinated to Ir(mpmppm)2 during the LC separation.
The measurement range of a Xevo G2 Tof MS detector manufactured by Waters Corporation, which was used in the analysis, was m/z=100 or more. That is why the ligand acac, which is out of the measurement range of the MS detector, was not detected. The ligand acac was not detected with a PDA detector, either.
Next, with the use of the results of LC/MS analysis shown in
As shown in Table 7, in Light-emitting Element 1, on the assumption that the total peak area of substances originating in the iridium complex Ir(mpmppm)2(acac) was 100%, the proportion of the peak area (b12) of a ligand not coordinated to the iridium metal to the peak area (b3, b7, and b8) of the iridium complex was 1.0%. In Light-emitting Element 2, on the assumption that the total peak area of substances originating in the iridium complex Ir(mpmppm)2(acac) was 100%, the proportion of the peak area (b12) of a ligand not coordinated to the iridium metal to the peak area (b3, b7, and b8) of the iridium complex was 0.8%. In Light-emitting Element 3, on the assumption that the total peak area of substances originating in the iridium complex Ir(mpmppm)2(acac) was 100%, the proportion of the peak area (b12) of a ligand not coordinated to the iridium metal to the peak area (b3, b7, and b8) of the iridium complex was 6.7%.
On the assumption that the total peak area of substances originating in the iridium complex was 100%, the proportion of the peak area of the ligand not coordinated to the iridium metal was 5% or less in Light-emitting Elements 1 and 2 that were embodiments of the present invention. Therefore, Light-emitting Elements 1 and 2 had a longer lifetime than Light-emitting Element 3 that was a comparative light-emitting element.
On the assumption that the total peak area of substances originating in the iridium complex was 100%, the proportion of the peak area of the ligand not coordinated to the iridium metal was 1% or less in Light-emitting Elements 1 and 2 that were embodiments of the present invention. Note that comparison between Light-emitting Element 1 and Light-emitting Element 2 shows that on the assumption that the total peak area of substances originating in the iridium complex is 100%, the proportion of the peak area of the ligand not coordinated to the iridium metal is smaller in Light-emitting Element 2 than in Light-emitting Element 1, which made the lifetime of Light-emitting Element 2 longer than that of Light-emitting Element 1. Therefore, it is suggested that on the assumption that the total peak area of substances originating in the iridium complex is 100%, a smaller proportion of the peak area of the ligand not coordinated to the iridium metal leads to higher reliability.
As described above, the reliability of the light-emitting elements of embodiments of the present invention was increased by reducing the concentration of an impurity originating in the iridium complex, which was the light-emitting substance in the light-emitting layers 510(1) and 510(2).
The results in Table 7 suggested that Ir(mpmppm)2(acac) was decomposed during the deposition by evaporation and a substance from which the ligand acac was dissociated was deposited by evaporation. The film deposited by evaporation contained Ir(mpmppm)2(acac) most as a main component, and also contained Structural Isomer 1 and Structural Isomer 2, which are presumably different from Ir(mpmppm)2(acac) in the direction of the ligand mpmppm. Since the proportion of an impurity from which a Me group was dissociated did not increase after the deposition by evaporation, a Me group is less likely to have been decomposed during the deposition by evaporation to be dissociated. As decomposition products that increased after the deposition by evaporation, the ligand mpmppm and Ir(mpmppm)2, from which the ligand acac was dissociated, were observed.
According to the results of the reliability tests shown in
The structures described in this example can be used in an appropriate combination with any of other examples and embodiments.
In this example, an example of fabricating a light-emitting element of one embodiment of the present invention will be described. Note that in this example, light-emitting elements that were embodiments of the present invention (Light-emitting Element 4 and Light-emitting Element 5) were fabricated.
A schematic cross-sectional view of Light-emitting Elements 4 and 5 is shown in
First, over the substrate 502, ITSO was deposited as the lower electrode 504 by a sputtering method. Note that the thickness of the lower electrode 504 was 100 nm and the area of the lower electrode 504 was 4 mm2 (2 mm×2 mm).
Then, for pretreatment before deposition of an organic compound layer by evaporation, the lower electrode 504 side of the substrate 502 provided with the lower electrode 504 was washed with water, baking was performed at 200° C. for 1 hour, and then UV ozone treatment was performed on a surface of the lower electrode 504 for 370 seconds.
After that, the substrate 502 was transferred into a vacuum evaporation apparatus where the pressure had been 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 502 was cooled down for approximately 30 minutes.
Next, the substrate 502 was fixed to a holder provided in the vacuum evaporation apparatus so that a surface of the substrate over which the lower electrode 504 was formed faced downward. In Example 2, by a vacuum evaporation method, the hole-injection layer 531, the hole-transport layer 532, the light-emitting layer 510(1), the light-emitting layer 510(2), the electron-transport layer 533(1), the electron-transport layer 533(2), the electron-injection layer 534, and the upper electrode 514 were sequentially formed. The fabrication method will be described in detail below.
First, after reducing the pressure of the vacuum evaporation apparatus to 10−4 Pa, DBT3P-II and molybdenum oxide were deposited by co-evaporation in a weight ratio of 2:1 (=DBT3P-II: molybdenum oxide), whereby the hole-injection layer 531 was formed over the lower electrode 504. Note that the thickness of the hole-injection layer 531 was 20 nm.
Then, as the hole-transport layer 532, BPAFLP was deposited by evaporation over the hole-injection layer 531. Note that the thickness of the hole-transport layer 532 was 20 nm.
Next, the light-emitting layer 510(1) was formed over the hole-transport layer 532. As the light-emitting layer 510(1), 2mDBTBPDBq-II, PCBBiF, and Ir(mpmppm)2(acac) were deposited by co-evaporation in a weight ratio of 0.7:0.3:0.05 (=2mDBTBPDBq-II: PCBBiF: Ir(mpmppm)2(acac)). Note that the thickness of the light-emitting layer 510(1) was 20 nm.
Next, the light-emitting layer 510(2) was formed over the light-emitting layer 510(1). As the light-emitting layer 510(2), 2mDBTBPDBq-II, PCBBiF, and Ir(mpmppm)2(acac) were deposited by co-evaporation in a weight ratio of 0.8:0.2:0.05 (=2mDBTBPDBq-II: PCBBiF: Ir(mpmppm)2(acac)). Note that the thickness of the light-emitting layer 510(2) was 20 nm.
In the light-emitting layer 510(1) and the light-emitting layer 510(2), 2mDBTBPDBq-II is a host material, PCBBiF is an assist material, and Ir(mpmppm)2(acac) is a phosphorescent material (a guest material).
Note that the purity of the iridium complex used in the deposition of the light-emitting layers by evaporation was different between Light-emitting Elements 4 and 5. In the deposition of the light-emitting layers by evaporation, the iridium complex that was represented as Material Z1 was used in Light-emitting Element 4, and the iridium complex that was represented as Material Z2 was used in Light-emitting Element 5. The purity of the iridium complexes that were represented as Materials Z1 and Z2 is shown in Table 9.
Note that the purity of Materials Z1 and Z2 was obtained by LC/MS analysis. The LC/MS analysis was performed by a method similar to that described in Example 1. As a result of the LC/MS analysis, chromatograms of Materials Z1 and Z2 exhibited peaks m1, m2, and m4 to m8 shown in Table 9. The peaks m1 to m8 are the same as those exhibited by the chromatograms of Materials Y1 to Y3 in Example 1.
As shown in Table 9, the total proportion of peak areas of substances other than the iridium complex to which the peaks m1 and m2 were assigned was 20.8% in Material Z1, and 7.8% in Material Z2.
After that, over the light-emitting layer 510(2), 2mDBTBPDBq-II was deposited by evaporation to a thickness of 5 nm as the electron-transport layer 533(1). Then, over the electron-transport layer 533(1), Bphen was deposited by evaporation to a thickness of 10 nm as the electron-transport layer 533(2). Then, over the electron-transport layer 533(2), LiF was deposited by evaporation to a thickness of 1 nm as the electron-injection layer 534.
Then, over the electron-injection layer 534, Al was deposited by evaporation to a thickness of 200 nm as the upper electrode 514.
Next, the sealing substrate 552 was prepared.
The light-emitting elements formed over the substrate 502 as described above were sealed by being bonded to the sealing substrate 552 in a glove box in a nitrogen atmosphere so as not to be exposed to the air. The sealing method was the same as that used for Light-emitting Elements 1 to 3 in Example 1.
Through the above process, Light-emitting Elements 4 and 5 were fabricated.
Note that in all the above evaporation steps for Light-emitting Elements 4 and 5, a resistive heating method was used as an evaporation method.
Next, reliability tests were performed on Light-emitting Elements 4 and 5. In the reliability tests, Light-emitting Elements 4 and 5 were driven under the conditions where the initial luminance was 5000 cd/m2 and the current density was constant.
The results in
The results in
Then, Light-emitting Elements 4 and 5 were analyzed by LC/MS to examine impurities contained in the light-emitting elements.
Note that for analysis of an impurity in Light-emitting Element 4, a light-emitting element that was different from Light-emitting Element 4 and was formed over the same substrate as Light-emitting Element 4 was used; and for analysis of an impurity in Light-emitting Element 5, a light-emitting element that was different from Light-emitting Element 5 and was formed over the same substrate as Light-emitting Element 5 was used. In each of the light-emitting elements for the impurity analysis, the area of the lower electrode 504 was approximately 12 cm2 (3.5 cm×3.3 cm). In other words, the light-emitting elements for the impurity analysis had the same materials and structures as Light-emitting Elements 4 and 5, but were different from Light-emitting Elements 4 and 5 in the area of the lower electrode 504. The samples for the impurity analysis were not driven; thus, the obtained results were not the analysis results of deteriorated objects produced by driving, but the analysis results of an impurity that had been contained from before driving. Here, the light-emitting element for the impurity analysis that was fabricated over the same substrate as Light-emitting Element 4 is regarded as Light-emitting Element 4 for convenience. The same applies to Light-emitting Element 5.
The LC/MS analysis was performed by a method similar to that described in Example 1.
In a manner similar to that of the analysis sample, the chloroform used for fabrication of the analysis sample was diluted with acetonitrile to give a solution, and the solution was analyzed to obtain a base-line (or background: BG) chromatogram. In
As shown in
As can be seen in
Next, the PDA chromatograms were analyzed with a focus on Ir(mpmppm)2(acac). The base line was subtracted in the analysis of the PDA chromatograms.
As shown in
The peaks c7 to c12 were analyzed using an MS chromatograph, which showed that the peak c7 was assigned to a structural isomer (referred to as Structural Isomer 1, for convenience) of Ir(mpmppm)2(acac); the peak c8, a structural isomer (referred to as Structural Isomer 2, for convenience) of Ir(mpmppm)2(acac); the peak c9, a substance with a structure of an mpmppm skeleton (a ligand of Ir(mpmppm)2(acac)) from which one Me group was dissociated; the peak c10, a substance with a structure of Ir(mpmppm)2, that is, a structure of Ir(mpmppm)2(acac) from which the ligand acac was dissociated; the peak c11, a substance with a structure of Ir(mpmppm)2(acac) from which the ligand acac and a Me group were dissociated; and the peak c12, mpmppm that was a ligand of Ir(mpmppm)2(acac).
In LC/MS analysis, the substance with the structure of Ir(mpmppm)2 produced an MS spectrum with a mass-to-charge ratio (m/z) of 753. The mass number of a proton adduct of a structure in which acetonitrile is coordinated to Ir(mpmppm)2 is 753. Thus, it was suggested that acetonitrile was coordinated to Ir(mpmppm)2 during the LC separation.
The measurement range of a Xevo G2 Tof MS detector manufactured by Waters Corporation, which was used in the analysis, was m/z=100 or more. That is why the ligand acac, which is out of the measurement range of the MS detector, was not detected. The ligand acac was not detected with a PDA detector, either.
Next, with the use of the results of LC/MS analysis shown in
As shown in Table 11, in Light-emitting Elements 4 and 5, the proportion of the peak area (c13) of a ligand not coordinated to the iridium metal was less than 0.1%, under the lower detection limit (shown in Table 11 as “-”).
On the assumption that the total peak area of substances originating in the iridium complex was 100%, the proportion of the peak area of the ligand not coordinated to the iridium metal was 1% or less in Light-emitting Elements 4 and 5 that were embodiments of the present invention. Therefore, Light-emitting Elements 4 and 5 had a long lifetime.
As described above, the reliability of the light-emitting elements of embodiments of the present invention was increased by reducing the concentration of the ligand mpmppm that was an impurity originating in the iridium complex, which was the light-emitting substance in the light-emitting layers 510(1) and 510(2).
The results in Table 11 suggested that Ir(mpmppm)2(acac) was decomposed during the deposition by evaporation and a substance from which the ligand acac was dissociated was deposited by evaporation. The film deposited by evaporation contained Ir(mpmppm)2(acac) most as a main component, and also contained Structural isomer 1 and Structural Isomer 2, which are presumably different from Ir(mpmppm)2(acac) in the direction of the ligand mpmppm. Since the proportion of an impurity from which a Me group was dissociated did not increase after the deposition by evaporation, a Me group is less likely to have been decomposed during the deposition by evaporation to be dissociated. As a decomposition product that increased after the deposition by evaporation, Ir(mpmppm)2, from which the ligand acac was dissociated, was observed. The ligand acac was not detected.
According to the results of the reliability tests shown in
The structures described in this example can be used in an appropriate combination with any of other examples and embodiments.
In this example, an example of fabricating a light-emitting element of one embodiment of the present invention will be described. Note that in this example, light-emitting elements that were embodiments of the present invention (Light-emitting Element 6 and Light-emitting Element 7) were fabricated.
A schematic cross-sectional view of Light-emitting Elements 6 and 7 is shown in
First, over the substrate 502, ITSO was deposited as the lower electrode 504 by a sputtering method. Note that the thickness of the lower electrode 504 was 100 nm and the area of the lower electrode 504 was 4 mm2 (2 mm×2 mm).
Then, for pretreatment before deposition of an organic compound layer by evaporation, the lower electrode 504 side of the substrate 502 provided with the lower electrode 504 was washed with water, baking was performed at 200° C. for 1 hour, and then UV ozone treatment was performed on a surface of the lower electrode 504 for 370 seconds.
After that, the substrate 502 was transferred into a vacuum evaporation apparatus where the pressure had been 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 502 was cooled down for approximately 30 minutes.
Next, the substrate 502 was fixed to a holder provided in the vacuum evaporation apparatus so that a surface of the substrate over which the lower electrode 504 was formed faced downward. In Example 3, by a vacuum evaporation method, the hole-injection layer 531, the hole-transport layer 532, the light-emitting layer 510(1), the light-emitting layer 510(2), the electron-transport layer 533(1), the electron-transport layer 533(2), the electron-injection layer 534, and the upper electrode 514 were sequentially formed. The fabrication method will be described in detail below.
First, after reducing the pressure of the vacuum evaporation apparatus to 10−4 Pa, DBT3P-II and molybdenum oxide were deposited by co-evaporation in a weight ratio of 2:1 (=DBT3P-II: molybdenum oxide), whereby the hole-injection layer 531 was formed over the lower electrode 504. Note that the thickness of the hole-injection layer 531 was 20 nm.
Then, as the hole-transport layer 532, BPAFLP was deposited by evaporation over the hole-injection layer 531. Note that the thickness of the hole-transport layer 532 was 20 nm.
Next, the light-emitting layer 510(1) was formed over the hole-transport layer 532. As the light-emitting layer 510(1), 2mDBTBPDBq-II, PCBBiF, and Ir(mpmppm)2(acac) were deposited by co-evaporation in a weight ratio of 0.7:0.3:0.05 (=2mDBTBPDBq-II: PCBBiF: Ir(mpmppm)2(acac)). Note that the thickness of the light-emitting layer 510(1) was 20 nm.
Next, the light-emitting layer 510(2) was formed over the light-emitting layer 510(1). As the light-emitting layer 510(2), 2mDBTBPDBq-II, PCBBiF, and Ir(mpmppm)2(acac) were deposited by co-evaporation in a weight ratio of 0.8:0.2:0.05 (=2mDBTBPDBq-II: PCBBiF: Ir(mpmppm)2(acac)). Note that the thickness of the light-emitting layer 510(2) was 20 nm.
In the light-emitting layer 510(1) and the light-emitting layer 510(2), 2mDBTBPDBq-II is a host material, PCBBiF is an assist material, and Ir(mpmppm)2(acac) is a phosphorescent material (a guest material).
Note that the purity of the iridium complex used in the deposition of the light-emitting layers by evaporation was different between Light-emitting Elements 6 and 7. In the deposition of the light-emitting layers by evaporation, the iridium complex that was represented as Material Z1 was used in Light-emitting Element 6, and the iridium complex that was represented as Material Z3 was used in Light-emitting Element 7. The purity of the iridium complexes that were represented as Materials Z1 and Z3 is shown in Table 13. Note that Material Z1 is the same as that used in Example 2.
Note that the purity of Materials Z1 and Z3 shown in Table 13 was obtained by LC/MS analysis. The LC/MS analysis was performed by a method similar to that described in Example 1. As a result of the LC/MS analysis, chromatograms of Materials Z1 and Z3 exhibited peaks m1 to m8 shown in Table 13. The peaks m1 to m8 are the same as those exhibited by the chromatograms of Materials Y1 to Y3 in Example 1.
As shown in Table 13, the total proportion of peak areas of substances other than the iridium complex to which the peaks m1 to m2 were assigned was 20.8% in Material Z1, and the total proportion of peak areas of substances other than the iridium complex to which the peaks m1 to m3 were assigned was 29% in Material Z3.
After that, over the light-emitting layer 510(2), 2mDBTBPDBq-II was deposited by evaporation to a thickness of 5 nm as the electron-transport layer 533(1). Then, over the electron-transport layer 533(1), Bphen was deposited by evaporation to a thickness of 10 nm as the electron-transport layer 533(2). Then, over the electron-transport layer 533(2), LiF was deposited by evaporation to a thickness of 1 nm as the electron-injection layer 534.
Then, over the electron-injection layer 534, Al was deposited by evaporation to a thickness of 200 nm as the upper electrode 514.
Next, the sealing substrate 552 was prepared.
The light-emitting elements formed over the substrate 502 as described above were sealed by being bonded to the sealing substrate 552 in a glove box in a nitrogen atmosphere so as not to be exposed to the air. The sealing method was the same as that in Example 1.
Through the above process, Light-emitting Elements 6 and 7 were fabricated.
Note that in all the above evaporation steps for Light-emitting Elements 6 and 7, a resistive heating method was used as an evaporation method.
Next, reliability tests were performed on Light-emitting Elements 6 and 7. In the reliability tests, Light-emitting Elements 6 and 7 were driven under the conditions where the initial luminance was 5000 cd/m2 and the current density was constant.
The results in
The results in
Then, Light-emitting Elements 6 and 7 were analyzed by LC/MS to examine impurities contained in the light-emitting elements.
Note that for analysis of an impurity in Light-emitting Element 6, a light-emitting element that was different from Light-emitting Element 6 and was formed over the same substrate as Light-emitting Element 6 was used; and for analysis of an impurity in Light-emitting Element 7, a light-emitting element that was different from Light-emitting Element 7 and was formed over the same substrate as Light-emitting Element 7 was used. In each of the light-emitting elements for the impurity analysis, the area of the lower electrode 504 was approximately 12 cm2 (3.5 cm×3.3 cm). In other words, the light-emitting elements for the impurity analysis had the same materials and structures as Light-emitting Elements 6 and 7, but were different from Light-emitting Elements 6 and 7 in the area of the lower electrode 504. The samples for the impurity analysis were not driven; thus, the obtained results were not the analysis results of deteriorated objects produced by driving, but the analysis results of an impurity that had been contained from before driving. Here, the light-emitting element for the impurity analysis that was fabricated over the same substrate as Light-emitting Element 6 is regarded as Light-emitting Element 6 for convenience. The same applies to Light-emitting Element 7.
The LC/MS analysis was performed by a method similar to that described in Example 1.
In a manner similar to that of the analysis sample, the chloroform used for fabrication of the analysis sample was diluted with acetonitrile to give a solution, and the solution was analyzed to obtain a base-line (or background: BG) chromatogram. In
As shown in
As can be seen in
Next, the PDA chromatograms were analyzed with a focus on Ir(mpmppm)2(acac). The base line was subtracted in the analysis of the PDA chromatograms.
As shown in
The peaks d7 to d13 were analyzed using an MS chromatograph, which showed that the peak d7 was assigned to a structural isomer (referred to as Structural Isomer 1, for convenience) of Ir(mpmppm)2(acac); the peak d8, a structural isomer (referred to as Structural Isomer 2, for convenience) of Ir(mpmppm)2(acac); the peaks d9 and d10, a substance with a structure of an mpmppm skeleton (a ligand of Ir(mpmppm)2(acac)) from which one Me group was dissociated; the peak d11, a substance with a structure of Ir(mpmppm)2, that is, a structure of Ir(mpmppm)2(acac) from which the ligand acac was dissociated; the peak d12, a substance with a structure of Ir(mpmppm)2(acac) from which the ligand acac and a Me group were dissociated; and the peak d13, mpmppm that was a ligand of Ir(mpmppm)2(acac).
In LC/MS analysis, the substance with the structure of Ir(mpmppm)2 produced an MS spectrum with a mass-to-charge ratio (m/z) of 753. The mass number of a proton adduct of a structure in which acetonitrile is coordinated to Ir(mpmppm)2 is 753. Thus, it was suggested that acetonitrile was coordinated to Ir(mpmppm)2 during the LC separation.
The measurement range of a Xevo G2 Tof MS detector manufactured by Waters Corporation, which was used in the analysis, was m/z=100 or more. That is why the ligand acac, which is out of the measurement range of the MS detector, was not detected. The ligand acac was not detected with a PDA detector, either.
Next, with the use of the results of LC/MS analysis shown in
As shown in Table 15, in Light-emitting Element 6, the peak area (d13) of a ligand not coordinated to the iridium metal was not detected. In Light-emitting Element 7, on the assumption that the total peak area of substances originating in the iridium complex Ir(mpmppm)2(acac) was 100%, the proportion of the peak area (d13) of a ligand not coordinated to the iridium metal to the peak area (d3, d7, and d8) of the iridium complex was 0.4%.
Therefore, Light-emitting Elements 6 and 7 that were embodiments of the present invention had a long lifetime because on the assumption that the total peak area of substances originating in the iridium complex was 100%, the proportion of the peak area of the ligand not coordinated to the iridium metal was 1% or less. In Light-emitting Element 6, the proportion of the peak area (d13) of a ligand not coordinated to the iridium metal was less than 0.1%, under the lower detection limit, indicating that Light-emitting Element 6 had higher reliability than Light-emitting Element 7 as shown in
As described above, the reliability of the light-emitting elements of embodiments of the present invention was increased by reducing the concentration of an impurity originating in the iridium complex, which was the light-emitting substance in the light-emitting layers 510(1) and 510(2).
The results in Table 15 suggested that Ir(mpmppm)2(acac) was decomposed during the deposition by evaporation and a substance from which the ligand acac was dissociated was deposited by evaporation. The film deposited by evaporation contained Ir(mpmppm)2(acac) most as a main component, and also contained Structural Isomer 1 and Structural Isomer 2, which are presumably different from Ir(mpmppm)2(acac) in the direction of the ligand mpmppm. Since the proportion of an impurity from which a Me group was dissociated did not increase after the deposition by evaporation, a Me group is less likely to have been decomposed during the deposition by evaporation to be dissociated. As a decomposition product that increased after the deposition by evaporation, Ir(mpmppm)2, from which the ligand acac was dissociated, was observed. The ligand acac was not detected.
According to the results of the reliability tests shown in
The structures described in this example can be used in an appropriate combination with any of other examples and embodiments.
This application is based on Japanese Patent Application serial no. 2014-218936 filed with Japan Patent Office on Oct. 28, 2014, the entire contents of which are hereby incorporated by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2014-218936 | Oct 2014 | JP | national |
