JP7299020B2 - Organic electroluminescence device and manufacturing method thereof - Google Patents

Description

TECHNICAL FIELD The present invention relates to an organic electroluminescence device and a manufacturing method thereof.

2. Description of the Related Art In recent years, organic electroluminescence display devices (hereinafter also simply referred to as “organic EL display devices”) have attracted attention as next-generation flat panel display devices. The organic EL display device is a self-luminous display device that can be made thin, has excellent visibility and viewing angle characteristics, and consumes low power.

This organic EL display device generally has a plurality of organic electroluminescence elements (hereinafter also simply referred to as "organic EL elements"). Each of the plurality of organic EL elements includes a first electrode formed on a substrate, an organic layer having a light-emitting layer formed on the first electrode, and a second electrode formed on the organic layer. there is By applying an electric field, the holes injected from the first electrode and the electrons injected from the second electrode recombine in the organic layer, and the light-emitting material forming the organic layer emits light. ing.

Further, the organic layer generally includes a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, an electron injection layer, and the like.

Here, the organic electroluminescence material (hereinafter also simply referred to as “organic EL material”) used in the organic layer can greatly affect the luminous efficiency and luminous life of the organic EL element. Therefore, organic EL materials are being researched that can achieve high efficiency and long life of organic EL elements.

For example, Patent Document 1 proposes an organic EL device in which a light-emitting layer is formed from an electron-transporting host and two kinds of triphenylene hosts by vapor deposition. Further, Patent Document 2 proposes an organic EL device formed by a vapor deposition method in which a light-emitting layer forming an exciton complex is formed from an electron-transporting host and a hole-transporting host.

2. Description of the Related Art In manufacturing an organic EL element, it is common to form an organic film forming an organic EL element by a dry film forming method such as a vapor deposition method. On the other hand, film formation by a dry film formation method such as a vapor deposition method is time-consuming and costly. (also referred to as )) is under consideration.

U.S. Patent Application Publication No. 2016/0093808 JP 2012-186461 A

However, when an organic EL element is formed by a wet film forming method such as a solution coating method, the organic EL material used for vapor deposition is difficult to dissolve in a coating solvent. In addition, after film formation, aggregation of organic molecules in the light-emitting layer is likely to occur. Therefore, the organic EL element formed by the coating method has a problem that sufficient luminous efficiency and luminous life are not obtained.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an organic electroluminescence device which can be produced by a coating method and which is excellent in luminous efficiency and luminous life.

The present inventors have conducted intensive research in order to solve the above problems. As a result, the inventors have found that the above problems can be solved by an organic electroluminescence device having a light-emitting layer containing three types of host compounds having specific structures, and have completed the present invention.

That is, according to one embodiment of the present invention, there is provided an organic electroluminescence device having a light-emitting layer between a pair of electrodes, wherein the light-emitting layer comprises at least one electron-transporting compound and at least one hole-transporting compound. a transportable compound and at least one wide-gap compound having a HOMO-LUMO energy gap of 3.3 eV or more;
The electron-transporting compound is a compound selected from the compound group (1) below, and/or the hole-transporting compound is a compound selected from the compound group (2) below. do.

Ar in compound group (1) and compound group (2) is each independently a substituted or unsubstituted aryl group or a substituted or unsubstituted heteroaryl group.

Further, according to another embodiment of the present invention, there is provided a method for manufacturing the above organic electroluminescence device.

ADVANTAGE OF THE INVENTION According to this invention, the organic electroluminescent element which can be produced by the coating method and is excellent in luminous efficiency and luminous life is provided.

1 is a schematic diagram showing an organic electroluminescence device according to one embodiment of the present invention; FIG.

Hereinafter, embodiments of the present invention will be described in detail. In addition, the present invention is not limited only to the following embodiments.

The present invention provides an organic electroluminescence device having a light-emitting layer between a pair of electrodes, wherein the light-emitting layer comprises at least one electron-transporting compound, at least one hole-transporting compound, and HOMO-LUMO and at least one wide-gap compound having an energy gap of 3.3 eV or more,
The electron-transporting compound is a compound selected from the following compound group (1), and/or the hole-transporting compound is a compound selected from the following compound group (2), the organic electroluminescence device. .

Ar in compound group (1) and compound group (2) is each independently a substituted or unsubstituted aryl group or a substituted or unsubstituted heteroaryl group.

The organic electroluminescence element of the present invention having such a structure can be produced by a coating method, and is excellent in luminous efficiency and luminous life.

Although the details of the reason why the organic electroluminescence device of the present invention achieves the above effects are unknown, the following mechanism is conceivable.

That is, by using a mixture of host compounds having three different properties without causing phase separation, the HOMO level and LUMO level are smoothed and the charge injection barrier is reduced. In addition, since the adjustment of the charge mobility can be controlled by the mixing ratio of the host compound, a high-performance device structure can be achieved.

It should be noted that the above mechanism is based on speculation, and its correctness or wrongness does not affect the technical scope of the present invention.

The electron-transporting compound, the hole-transporting compound, and the wide-gap compound contained in the light-emitting layer according to the invention will be described below in order. In this specification, the electron-transporting compound is also simply referred to as "ET-Host", and the hole-transporting compound is simply referred to as "HT-Host". Also, the wide-gap compound is simply referred to as "WG-Host". Furthermore, the electron-transporting compound, the hole-transporting compound, and the wide-gap compound are collectively referred to as a "host compound".

According to one embodiment of the present invention, the electron-transporting compound is a compound selected from the above compound group (1), and/or the hole-transporting compound is a compound selected from the above compound group (2). be. The above "or" means (a) a form in which the electron-transporting compound is a compound selected from the compound group (1), and (b) a form in which the hole-transporting compound is selected from the compound group (2). It means that the compound satisfies any one of the forms. In addition, the above "and" means (a) a form in which the electron-transporting compound is a compound selected from the compound group (1), and (b) a form in which the hole-transporting compound is selected from the compound group (2) It means satisfying both forms of a compound. From the viewpoint of further improving the effects of the present invention, it is preferable to satisfy both of the forms (a) and (b).

<Electron transport compound (ET-Host)>
The electron-transporting compound according to the present invention is preferably a compound selected from the following compound group (1) from the viewpoint of efficiently exhibiting the effects of the present invention.

In the above compound group (1),
Each Ar is independently a substituted or unsubstituted aryl group or a substituted or unsubstituted heteroaryl group.

As used herein, the term "substituted or unsubstituted" means that substituents and the like may have substituents other than hydrogen atoms and deuterium atoms. Moreover, these substituents may combine with each other to form a ring. Furthermore, in the present specification, "independently" means that each substituent may be the same or different.

The electron-transporting compound can be used alone or in combination of two or more. Moreover, a commercially available product or a synthetic product may be used as the electron-transporting compound.

The aryl group that can constitute Ar in the compound group (1) is not particularly limited, but a monovalent group containing one or more aromatic hydrocarbon rings having 6 to 30 carbon atoms (aromatic hydrocarbon ring group ) is preferred. When the aromatic hydrocarbon ring group contains two or more rings, the two or more rings may be fused together. It may also be in the form of a hydrocarbon ring-aggregating group in which two or more rings are directly bonded via single bonds.

Aromatic hydrocarbons constituting the aromatic hydrocarbon ring group are not particularly limited, but specific examples include benzene, pentalene, indene, naphthalene, anthracene, azulene, heptalene, acenaphthalene, phenalene, fluorene, spirobifluorene, phenanthrene, biphenyl, o-terphenyl, m-terphenyl, p-terphenyl, quaterphenyl, 1,3,5-triphenylbenzene, kinkphenyl, sexiphenyl, septiphenyl, triphenylene, pyrene, chrysene, picene, perylene, Pentaphen, pentacene, tetraphene, hexaphene, hexacene, rubicene, trinaphthylene, heptaphene, pyrantrene and the like.

The heteroaryl group that can constitute Ar is not particularly limited, but is an aromatic heterocyclic ring having 3 or more and 30 or less ring-forming atoms having one or more heteroatoms and the remaining ring atoms being carbon atoms (C). is preferably a monovalent group (aromatic heterocyclic group) containing one or more of When the heteroaromatic group contains two or more rings, the two or more rings may be fused together. In addition, one or more hydrogen atoms present in these aromatic heterocyclic groups may be substituted with a substituent.

Examples of the heteroatom include nitrogen atom (N), oxygen atom (O), phosphorus atom (P), sulfur atom (S) and the like. A nitrogen atom (N) is preferred.

Here, the number of ring-forming atoms means the number of atoms constituting the ring itself in a compound having a structure in which atoms are cyclically bonded (for example, a single ring, a condensed ring, or a ring assembly). Atoms that do not constitute a ring (for example, a hydrogen atom that terminates a bond of an atom that constitutes a ring), and when the ring is substituted with a substituent, the atoms contained in the substituent are not included in the number of ring-forming atoms. For example, a carbazolyl group has 13 ring atoms.

Specific examples of the aromatic heterocyclic ring constituting the aromatic heterocyclic group include pyridine, pyrazine, pyridazine, pyrimidine, triazine, quinoline, isoquinoline, quinoxaline, quinazoline, naphthyridine, acridine, phenazine, benzoquinoline, benzoisoquinoline, phenanthridine, phenanthroline, benzoquinone, coumarin, anthraquinone, fluorenone, furan, thiophene, benzofuran, benzothiophene, dibenzofuran, dibenzothiophene, pyrrole, indole, carbazole, imidazole, benzimidazole, pyrazole, indazole, oxazole, isoxazole, benzoxazole , benzoisoxazole, thiazole, isothiazole, benzothiazole, benzisothiazole, imidazolinone, benzimidazolinone, imidazopyridine, imidazopyrimidine, imidazophenanthridine, benzimidazophenanthridine, azadibenzofuran, azacarbazole, azadibenzothiophene , diazadibenzofuran, diazacarbazole, diazadibenzothiophene, xanthone, thioxanthone, and the like.

As described above, one or more hydrogen atoms present in the aromatic hydrocarbon ring group and the aromatic heterocyclic ring group may be substituted with a substituent. Specific examples of the substituent include, for example, a substituted or unsubstituted alkyl group having 1 to 30 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 30 carbon atoms, and a substituted or unsubstituted 6 to 30 carbon atoms. The following aryloxy groups, substituted or unsubstituted secondary or tertiary amino groups having 1 to 30 carbon atoms, cyano groups, substituted or unsubstituted aryl groups having 6 to 30 carbon atoms, or substituted or unsubstituted A substituted heteroaryl group having 3 or more and 30 or less ring-forming atoms is exemplified.

Specific examples of the triazine compound represented by Formula 1-A include the following compounds.

In the triazine compound represented by the general formula 1-A, it is more preferable that the three Ars bonded to the triazine ring have different structures. Such a structure can reduce the crystallinity of the compound and increase the solubility of the compound.

Specific examples of the compounds represented by general formulas 1-B, 1-C, 1-D, and 1-E include compounds represented by general formula 1-A in which the triazine ring is a pyrimidine ring, pyridazine ring, pyrazine ring , and pyridine rings.

Specific examples of the quinazoline compounds and quinoline compounds represented by general formulas 1-F and 1-G include the following compounds. In addition to these, compounds in which the triazine ring in the exemplary compound of general formula 1-A is replaced with a quinazoline ring and a quinoline ring can be mentioned.

Specific examples of the phosphine oxide compound represented by formula 1-H include the following compounds.

Specific examples of the anthracene compound represented by Formula 1-I include the following compounds.

Specific examples of the tetracene compound represented by Formula 1-J include the following compounds.

Specific examples of the tetraphene compound represented by Formula 1-K include the following compounds.

From these electron-transporting compounds, it is preferable to select an appropriate material from the viewpoint of the type of dopant, emission color, and the like.

Preferred electron-transporting compounds for green phosphorescence are ET-Host-A to F below.

Further preferred electron-transporting compounds for green phosphorescence are ET-Host-E or ET-Host-F compounds below.

The content of the electron-transporting compound in the host compound is preferably 10% by mass or more and 80% by mass or less, and preferably 25% by mass or more and 60% by mass or less, with the total mass of the host compound being 100% by mass. more preferred.

In particular, from the viewpoint of further improving the current efficiency, the content of the electron-transporting compound in the host compound is preferably 30% by mass or more and 50% by mass or less based on 100% by mass of the total mass of the host compound. From the viewpoint of further improving durability, the content of the electron-transporting compound in the host compound is preferably 35% by mass or more and 55% by mass or less when the total mass of the host compound is 100% by mass.

<Hole-transporting compound (HT-Host)>
From the viewpoint of efficiently exhibiting the effects of the present invention, the hole-transporting compound according to the present invention is preferably a compound selected from the following compound group (2).

In the above compound group (2),
Each Ar is independently a substituted or unsubstituted aryl group or a substituted or unsubstituted heteroaryl group.

Descriptions of the aryl group and heteroaryl group that can constitute Ar in the compound group (2) are the same as those described in the section on the electron-transporting compound, and thus the description is omitted here.

The hole-transporting compounds can be used alone or in combination of two or more. Moreover, a commercially available product or a synthetic product may be used as the hole-transporting compound.

Specific examples of hole-transporting compounds include the following compounds.

Among these hole-transporting compounds, the following HT-Host-A to D compounds are preferred from the viewpoint of solubility in the solvent used and hole-injecting properties. More preferred are the following HT-Host-A or HT-Host-B compounds.

The content of the hole-transporting compound in the host compound is preferably 10% by mass or more and 80% by mass or less, more preferably 20% by mass or more and 60% by mass or less, with the total mass of the host compound being 100% by mass. .

<Wide gap compound (WG-Host)>
A wide gap compound according to the present invention is a compound having a HOMO-LUMO energy gap (Eg) of 3.3 eV or more. When the HOMO-LUMO energy gap (Eg) is less than 3.3 eV, the life-extending effect obtained by applying the wide-gap compound as the host material is reduced. Although the upper limit of the HOMO-LUMO energy gap (Eg) is not particularly limited, it is preferably 4 eV or less.

A wide gap compound can be used individually or in combination of 2 or more types. Moreover, a commercial item may be used for a wide gap compound, and a synthesized product may be used.

From the viewpoint of efficiently expressing the effects of the present invention, the wide gap compound is preferably a compound selected from the following compound group (3).

In the above compound group (3),
Ar ₁ is each independently a hydrogen atom, a substituted or unsubstituted aryl group, or a substituted or unsubstituted monovalent nitrogen-containing heterocyclic group, provided that two Ar ₁ are hydrogen atoms at the same time Not,
Ar ₂ is each independently a phenyl group, a hydrocarbon ring assembly group in which multiple aromatic hydrocarbon rings are directly bonded via a single bond, or a substituted or unsubstituted heteroaryl group;
each Ar ₃ is independently a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group, or a substituted or unsubstituted heteroaryl group;
Ar ₄ is a hydrogen atom, a substituted or unsubstituted aryl group, or a substituted or unsubstituted heteroaryl group.

The substituted or unsubstituted aryl group that can constitute Ar ₁ , Ar ₃ and Ar ₄ is the same as described above, and the description thereof is omitted here. Also, the substituted or unsubstituted heteroaryl group that can constitute Ar ₂ , Ar ₃ and Ar ₄ is the same as described above, and the description is omitted here.

A substituted or unsubstituted monovalent nitrogen-containing heterocyclic group that can constitute Ar ₁ has at least one nitrogen atom and has 3 or more and 30 or less ring-forming atoms and does not have a sulfur atom and an oxygen atom. It is a monovalent group (nitrogen-containing heterocyclic group) containing one or more nitrogen-containing heterocycles. When a nitrogen-containing heterocyclic group contains more than one ring, the two or more rings may be fused together. Also, one or more hydrogen atoms present in the nitrogen-containing heterocyclic group may be substituted with a substituent. Specific examples of the substituent are the same as those described above for the aromatic hydrocarbon ring group and the aromatic heterocyclic group.

Specific examples of the nitrogen-containing heterocyclic ring constituting the nitrogen-containing heterocyclic group include pyridine, pyrazine, pyridazine, pyrimidine, triazine, quinoline, isoquinoline, quinoxaline, quinazoline, naphthyridine, acridine, phenazine, benzoquinoline, benzoisoquinoline, phenanth. Lysine, phenanthroline, pyrrole, indole, carbazole, imidazole, benzimidazole, pyrazole, indazole, imidazopyridine, imidazopyrimidine, imidazophenanthridine, benzimidazophenanthridine, azacarbazole, diazacarbazole and the like.

The hydrocarbon ring-aggregating group that can constitute Ar ₂ is a monovalent group in which a plurality of aromatic hydrocarbon rings are directly bonded via single bonds. Examples of aromatic hydrocarbon rings include benzene, pentalene, indene, naphthalene, anthracene, azulene, heptalene, acenaphthalene, phenalene, fluorene, spirobifluorene, phenanthrene, biphenyl, o-terphenyl, m-terphenyl, p -terphenyl, quaterphenyl, kinkphenyl, sexiphenyl, septiphenyl, triphenylene, pyrene, chrysene, picene, perylene, pentaphene, pentacene, tetraphene, hexaphene, hexacene, rubicene, trinaphthylene, heptaphene, pyrantrene and the like. The plural aromatic hydrocarbon rings may be the same or different. Also, one or more hydrogen atoms present in the aromatic hydrocarbon ring may be substituted with a substituent. Specific examples of the substituent are the same as those described above for the aromatic hydrocarbon ring group and the aromatic heterocyclic group.

The alkyl group that can constitute Ar ₃ is not particularly limited, but is preferably, for example, a linear or branched alkyl group having 1 to 30 carbon atoms. Specifically, methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, n-pentyl group, isopentyl group, tert-pentyl group, neopentyl group, 1,2-dimethylpropyl group, n-hexyl group, isohexyl group, 1,3-dimethylbutyl group, 1-isopropylpropyl group, 1,2-dimethylbutyl group, n-heptyl group, 1,4- dimethylpentyl group, 3-ethylpentyl group, 2-methyl-1-isopropylpropyl group, 1-ethyl-3-methylbutyl group, n-octyl group, 2-ethylhexyl group, 3-methyl-1-isopropylbutyl group, 2 -methyl-1-isopropyl group, 1-tert-butyl-2-methylpropyl group, n-nonyl group, 3,5,5-trimethylhexyl group, n-decyl group, isodecyl group, n-undecyl group, 1- methyldecyl group, n-dodecyl group, n-tridecyl group, n-tetradecyl group, n-pentadecyl group, n-hexadecyl group, n-heptadecyl group, n-octadecyl group, n-nonadecyl group, n-eicosyl group, n- Heneicosyl group, n-docosyl group, n-tricosyl group, n-tetracosyl group and the like can be mentioned. Among these, linear or branched alkyl groups having 1 to 8 carbon atoms are preferred.

One or more hydrogen atoms present in the alkyl group may be substituted with a substituent. Specific examples of the substituent are the same as those described for the aromatic hydrocarbon ring group and the aromatic heterocyclic group. However, it is never substituted with an alkyl group.

Specific examples of the triphenylene compound represented by Formula 3-A include the following compounds.

Specific examples of the dibenzofuran compound represented by Formula 3-B include the following compounds.

In the dibenzofuran compound represented by general formula 3-B, it is more preferable that two Ar ₂ bonds to the dibenzofuran ring have different structures. Such a structure can reduce the crystallinity of the compound and increase the solubility of the compound.

Specific examples of the dibenzothiophene compound represented by general formula 3-C include the following compounds.

Specific examples of the fluorene compound represented by formula 3-D include the following compounds.

Specific examples of the dicarbazole compound represented by Formula 3-E include the following compounds.

Among these wide gap compounds, in the examples, the following WG-Host- AF were selected as preferred compounds.

More preferred are compounds of WG-Host-A, WG-Host-D, or WG-Host-E below.

More preferred are the following WG-Host-A or WG-Host-D compounds.

The content of the wide gap compound in the host compound is preferably 15% by mass or more and 40% by mass or less, more preferably 16% by mass or more and 35% by mass or less, with the total mass of the host compound being 100% by mass. preferable.

The host compound according to the present embodiment described above exhibits high solubility in a solvent, and can be easily formed into a film (thin film) by a wet coating method. In addition, the organic EL device having the light-emitting layer containing the above host compound can improve the luminous efficiency and luminous life even when it is produced by a wet coating method (solution coating method).

[Organic electroluminescence element (organic EL element)]
Hereinafter, the organic electroluminescence device (organic EL device) according to the present embodiment will be described in detail with reference to FIG. FIG. 1 is a schematic diagram showing an organic EL device according to this embodiment. However, the structure of the organic EL element according to this embodiment is not limited to the form shown in FIG.

As shown in FIG. 1, the organic EL element 100 according to this embodiment includes a substrate 110, a first electrode 120 arranged on the substrate 110, and a hole injection layer 130 arranged on the first electrode 120. , a hole-transporting layer 140 disposed on the hole-injecting layer 130, a light-emitting layer 150 disposed on the hole-transporting layer 140, an electron-transporting layer 160 disposed on the light-emitting layer 150, and an electron-transporting layer An electron injection layer 170 disposed on 160 and a second electrode 180 disposed on the electron injection layer 170 .

The light-emitting layer 150 of the present embodiment is formed by applying and drying a light-emitting layer-forming composition containing a host compound and a solvent. That is, the present invention comprises at least one electron-transporting compound, at least one hole-transporting compound, at least one wide-gap compound having a HOMO-LUMO energy gap of 3.3 eV or more, and a solvent. wherein the electron-transporting compound is a compound selected from the compound group (1) and/or the hole-transporting The organic compound is a compound selected from the above compound group (2).

<Composition for forming light-emitting layer>
The composition for forming a light-emitting layer according to this embodiment is used for forming a light-emitting layer of an organic EL element by a coating method. Such a composition for forming a light-emitting layer contains the host compound according to the present invention and a solvent.

Any solvent can be used as long as it can dissolve the host compound. Specifically, for example, toluene, xylene, ethylbenzene, diethylbenzene, mesitylene, propylbenzene, cyclohexylbenzene, dimethoxybenzene ene), Anisole, ethoxytoluene, phenoxytoluene, isopropylbiphenyl, dimethylanisole, phenyl acetate, phenyl propionic acid d), methyl benzoate ( methyl benzoate), ethyl benzoate, and the like. These solvents can be used alone or in combination of two or more.

The amount of solvent used is not particularly limited. However, from the viewpoint of ease of application, the concentration of the host compound is preferably 0.1% by mass or more and 10% by mass or less, more preferably 0.5% by mass or more and 5% by mass or less.

Specific examples of the solution coating method include a spin coat method, a casting method, a micro gravure coat method, a gravure coat method, a bar coat method, and a roll coating method. roll coat method, wire bar coat method, dip coat method, spray coat method, screen printing method, flexographic printing method, offset ) printing method, ink jet printing method, and the like.

After applying the composition for forming a light-emitting layer to form a coating film, the coating film is dried to form a light-emitting layer.

Note that the method for forming layers other than the light-emitting layer is not particularly limited. Such layers other than the light-emitting layer may be formed by, for example, a vacuum deposition method or a solution coating method.

The substrate 110 can use a substrate used in general organic EL devices. For example, the substrate 110 may be a glass substrate, a semiconductor substrate such as a silicon substrate, or a transparent plastic substrate.

A first electrode 120 is formed on the substrate 110 . Specifically, the first electrode 120 is an anode, and is formed of a metal, an alloy, a conductive compound, or the like having a large work function. For example, the first electrode 120 is made of indium tin oxide (In ₂ O ₃ —SnO ₂ : ITO), indium zinc oxide (In ₂ O ₃ —ZnO), tin oxide (SnO ₂ ), oxide A transmissive electrode may be formed of zinc (ZnO) or the like. Also, the first electrode 120 may be formed as a reflective electrode by laminating magnesium (Mg), aluminum (Al), or the like on the transparent conductive film.

A hole injection layer 130 is formed on the first electrode 120 . The hole injection layer 130 is a layer that facilitates the injection of holes from the first electrode 120, and is specifically formed with a thickness of 10 nm or more and 1000 nm or less, more specifically 10 nm or more and 100 nm or less. good too.

The hole injection layer 130 can be formed using a known hole injection material. Examples of known hole injection materials that form the hole injection layer 130 include poly(ether ketone)-containing triphenylamine (TPAPEK), 4-isopropyl-4'-methyldiphenyliodonium tetrakis. (Pentafluorophenyl) borate (4-isopropyl-4′-methyldiphenyliodonium tetrakis (pentafluorophenyl) borate: PPBI), N,N′-diphenyl-N,N′-bis-[4-(phenyl-m-tolyl-amino) -phenyl]-biphenyl-4,4'-diamine (N,N'-diphenyl-N,N'-bis-[4-(phenyl-m-tolyl-amino)-phenyl]-biphenyl-4,4'- diamine: DNTPD), copper phthalocyanine, 4,4′,4″-tris(3-methylphenylphenylamino)triphenylamine (4,4′,4″-tris(3-methylphenylphenylamino)triphenylamine: m -MTDATA), N,N'-di(1-naphthyl)-N,N'-diphenylbenzidine (N,N'-di(1-naphthyl)-N,N'-diphenylbenzidine: NPB), 4,4' ,4″-tris(diphenylamino)triphenylamine (4,4′,4″-tris(diphenylamino)triphenylamine: TDATA), 4,4′,4″-tris(N,N-2-naphthylphenylamino) Triphenylamine (4,4′,4″-tris(N,N-2-naphthylphenylamino) triphenylamine: 2-TNATA), polyaniline/dodecylbenzenesulphonic acid, poly(3,4-ethylenediethylene oxythiophene)/poly(4-styrenesulfonate) (poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate), PEDOT-PSS), and polyaniline/10-camphorsulfonic acid, etc. can be mentioned.

A hole transport layer 140 is formed on the hole injection layer 130 . The hole transport layer 140 is a layer having a function of transporting holes, and may be formed with a thickness of 10 nm or more and 150 nm or less, for example.

Hole transport layer 140 can be formed using a known hole transport material. Examples of known hole transport materials include 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC), N- Carbazole derivatives such as N-phenylcarbazole and polyvinylcarbazole, N,N'-bis(3-methylphenyl)-N,N'-diphenyl-[1,1-biphenyl]-4 ,4′-diamine (N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1-biphenyl]-4,4′-diamine: TPD), 4,4′,4″ -tris(N-carbazolyl)triphenylamine (4,4′,4″-tris(N-carbazolyl)triphenylamine: TCTA) and N,N′-di(1-naphthyl)-N,N′-diphenylbenzidine (N,N'-di(1-naphthyl)-N,N'-diphenylbenzidine: NPB) and the like.

In addition, hole transport materials described in International Publication No. 2011/159872, US Patent Application Publication No. 2016/0315259, etc. can also be used.

A light emitting layer 150 is formed on the hole transport layer 140 . The light-emitting layer 150 is a layer that emits light by fluorescence, phosphorescence, or the like. The light-emitting layer 150 contains the host compound according to this embodiment and is formed by the coating method described above. The light emitting layer 150 may be formed with a thickness of, for example, 10 nm or more and 60 nm or less.

The light-emitting layer 150 may contain a hole-transporting compound (HT-Host) or an electron-transporting compound (ET-Host) other than the host compound according to this embodiment. Examples of such other compounds include tris(8-quinolinato)aluminum (Alq ₃ ), 4,4′-bis(carbazol-9-yl)biphenyl(4,4 '-bis (carbazol-9-yl) biphenyl: CBP), poly (n- vinyl carbazole) (poly (n-vinyl carbazole): PVK), 9,10-di (naphthalen-2-yl) anthracene (9, 10-di(naphthalene)anthracene: ADN), 4,4′,4″-tris(N-carbazolyl)triphenylamine (4,4′,4″-tris(N-carbazolyl)triphenylamine: TCTA), 1, 3,5-tris(N-phenylbenzimidazol-2-yl)benzene (1,3,5-tris(N-phenyl-benzimidazol-2-yl)benzene: TPBI), 3-tert-butyl-9,10 -di(naphth-2-yl)anthracene (3-tert-butyl-9,10-di(naphth-2-yl)anthracene: TBADN), distyrylarylene (DSA), 4,4'-bis ( 9-carbazole)-2,2'-dimethyl-biphenyl (4,4'-bis(9-carbazole)2,2'-dimethylbiphenyl: dmCBP) and the like.

The light-emitting layer 150 preferably contains a fluorescent compound or a phosphorescent compound as a dopant material. Specific examples of fluorescent compounds include perylene and its derivatives, rubrene and its derivatives, coumarin and its derivatives, pyrene and its derivatives, 4-dicyanomethylene-2 -(p-dimethylaminostyryl)-6-methyl-4H-pyran (4-dicyanomethylene-2-(p-dimethylaminostyryl)-6-methyl-4H-pyran: DCM) and derivatives thereof. Further, specific examples of the phosphorescent compound include bis[2-(4,6-difluorophenyl)pyridinate]picolinate iridium (III) (bis[2-(4,6-difluorophenyl)pyridinate]picolinate iridium (III): FIrPic), bis (1-phenylisoquinoline) (acetylacetonate) iridium (III) (bis (1-phenylisoquinoline) (acetylacetonate) iridium (III): Ir (piq) ₂ (acac)), tris ( 2-phenylpyridine)iridium (III) (tris(2-phenylpyridine)iridium (III): Ir(ppy) ₃ ), tris(2-(3-p-xyl)phenyl)pyridine iridium (III) (tris(2 -(3-p-xylyl)phenyl)pyridine iridium (III), TEG) and other iridium (Ir) complexes, osmium (Os) complexes, platinum (Pt) complexes, and the like.

The lower limit of the content of the hole-transporting compound in the light-emitting layer is preferably more than 20% by mass, more preferably 25% by mass or more, based on 100% by mass of the total mass of the light-emitting layer. Within this range, there is an advantage that necessary and sufficient holes are supplied to the light-emitting layer, and low-voltage and highly efficient light emission can be obtained. The upper limit of the content of the hole-transporting compound in the light-emitting layer is preferably 70% by mass or less, more preferably 55% by mass or less, based on 100% by mass of the total mass of the light-emitting layer.

An electron transport layer 160 is formed on the light emitting layer 150 . The electron transport layer 160 is a layer having a function of transporting electrons, and is formed using a vacuum deposition method, a spin coating method, an inkjet printing method, or the like. The electron transport layer 160 may be formed with a thickness of, for example, 15 nm or more and 50 nm or less.

Electron transport layer 160 may be formed using a known electron transport material. Known electron transport materials include, for example, tris(8-quinolinato)aluminum (Alq ₃ ), (8-hydroxyquinolinato)lithium (lithium quinolate, (8-hydroxyquinolinato)lithium : Liq), and compounds having a nitrogen-containing aromatic ring. Specific examples of the compound having a nitrogen-containing aromatic ring include, for example, 1,3,5-tri[(3-pyridyl)-phen-3-yl]benzene (1,3,5-tri[(3-pyridyl) -phen-3-yl]benzene), 2,4,6-tris(3′-(pyridin-3-yl)biphenyl-3-yl)-1,3, compounds containing a triazine ring, such as 5-triazine (2,4,6-tris(3′-(pyridin-3-yl)biphenyl-3-yl)-1,3,5-triazine), 2 -(4-(N-phenylbenzoinidazolyl-1-yl-phenyl)-9,10-dinaphthylanthracene (2-(4-(N-phenylbenzoimidazolyl-1-yl-phenyl)-9,10-dinaphthylanthracene) ), KLET-01, KLET-02, KLET-03, KLET-10, KLET-M1 (manufactured by Chemipro Kasei Co., Ltd.) and the like.

An electron injection layer 170 is formed on the electron transport layer 160 . The electron injection layer 170 is a layer having a function of facilitating injection of electrons from the second electrode 180, and is formed using a vacuum deposition method or the like. The electron injection layer 170 may be formed with a thickness of, for example, 0.3 nm or more and 9 nm or less. For the electron injection layer 170, any known material for forming the electron injection layer 170 can be used. For example, the electron injection layer 170 may include (8-hydroxyquinolinato)lithium (Liq) and lithium compounds such as lithium fluoride (LiF), sodium chloride (NaCl), fluoride It may be made of cesium (CsF), lithium oxide (Li ₂ O), barium oxide (BaO), or the like.

A second electrode 180 is formed on the electron injection layer 170 . The second electrode 180 is specifically a cathode, and is formed of a metal, an alloy, a conductive compound, or the like, which has a small work function. For example, the second electrode 180 is made of metal such as lithium (Li), magnesium (Mg), aluminum (Al), calcium (Ca), aluminum-lithium (Al-Li), magnesium-indium (Mg-In), An alloy such as magnesium-silver (Mg--Ag) may be formed as a reflective electrode. In addition, the second electrode 180 is a transparent conductive film such as a thin film of 20 nm or less of the above metal material, indium tin oxide (In ₂ O ₃ —SnO ₂ ) and indium zinc oxide (In ₂ O ₃ —ZnO). It may be formed as an electrode.

Note that the layered structure of the organic EL element 100 according to the present embodiment is not limited to the above example. The organic EL element 100 according to this embodiment may be formed with another known laminated structure. For example, the organic EL device 100 may omit one or more of the hole injection layer 130, the hole transport layer 140, the electron transport layer 160, and the electron injection layer 170, and may additionally include other layers. may be provided. Moreover, each layer of the organic EL element 100 may be formed of a single layer, or may be formed of a plurality of layers.

For example, the organic EL device 100 may further include a hole blocking layer between the hole transport layer 140 and the light emitting layer 150 to prevent excitons or holes from diffusing into the electron transport layer 160. good too. The hole blocking layer can be formed by, for example, an oxadiazole derivative, a triazole derivative, a phenanthroline derivative, or the like.

The present invention will be described in more detail using the following examples and comparative examples, but the technical scope of the present invention is not limited only to the following examples.

The structures of ET-Host, HT-Host, and WG-Host used in Examples and Comparative Examples are as shown in the chemical formulas below. WG-Host also shows the value of the HOMO-LUMO energy gap (Eg).

<Preparation of organic electroluminescence element>
(Example 1)
A polymer P-1 represented by the following chemical formula was synthesized according to the method for producing Compound T described in International Publication No. 2011/159872. P-1 had a number average molecular weight (Mn) of 141,000 and a weight average molecular weight (Mw) of 511,000 as determined by gel permeation chromatography (GPC).

In addition, FA-14 (see the chemical formula below) described in US Patent Application Publication No. 2016/0315259 was synthesized by a standard method.

Three host compounds (ET-Host-A, HT-Host-A, WG-Host-A) and the dopant material tris(2-(3-p-xyl)phenyl)pyridine iridium(III) (TEG , see the following chemical formula) was dissolved in methyl benzoate to prepare a light-emitting layer coating solution (light-emitting layer-forming composition) having a solid content of 4% by mass. At this time, the mass ratio of ET-Host-A, HT-Host-A and WG-Host-A was 1:1:1. Also, the doping amount of the dopant material was set to 10% by mass with respect to the total mass of the light-emitting layer.

As a first electrode (anode), a glass substrate was prepared on which a stripe-shaped indium tin oxide (ITO) film was formed with a film thickness of 150 nm. PEDOT-PSS (manufactured by Sigma-Aldrich) was applied to a glass substrate by a spin coating method so as to have a dry film thickness of 15 nm and dried to form a hole injection layer.

Next, P-1 and FA-14 were dissolved in anisole (solvent) to prepare a hole transport layer coating solution. The content of FA-14 was set to 20% by mass with respect to the total mass of the hole transport layer. The hole transport layer coating liquid was applied onto the hole injection layer formed above by a spin coating method and dried to form a hole transport layer having a dry film thickness of 125 nm. Next, the above-obtained luminescent layer coating solution was applied onto the formed hole transport layer by spin coating and dried at 240° C. for 30 minutes to form a luminescent layer having a dry film thickness of 55 nm. bottom.

(8-Hydroxyquinolinolato)lithium (Liq) and KLET-03 (manufactured by Chemipro Kasei Co., Ltd.) are co-coated at a mass ratio of 1:1 on the light-emitting layer formed above by a vacuum deposition method. It was evaporated to form an electron transport layer with a thickness of 20 nm. Next, lithium fluoride (LiF) was vapor-deposited on this electron-transporting layer by a vacuum vapor deposition method to form an electron-injecting layer with a thickness of 3.5 nm.

A second electrode (cathode) having a thickness of 100 nm was formed by vapor-depositing aluminum (Al) on the formed electron injection layer by a vacuum vapor deposition method. Thus, an organic EL device was produced.

(Examples 2-3, Comparative Examples 1-2)
An organic electroluminescence device was produced in the same manner as in Example 1, except that the content mass ratio of the host compound was changed as shown in Table 1 below.

[evaluation]
The luminous efficiency and luminous life of the produced organic electroluminescence device were evaluated by the following methods. The luminous efficiency was evaluated by current efficiency (cd/A).

A predetermined voltage was applied to each organic electroluminescence element using a DC constant voltage power supply (source meter manufactured by Keyence Corporation) to cause the organic electroluminescence element to emit light. While measuring the light emission of the organic electroluminescence element with a luminance measuring device (SR-3, manufactured by Topcon Co., Ltd.), the current was gradually increased, and when the luminance reached 6000 nit (cd/m ² ), the current was kept constant. , abandoned. Here, the current value (current density) per unit area is calculated from the area of the organic electroluminescence element, and the brightness (cd/m ² ) is divided by the current density (A/m ² ) to obtain the "current efficiency (cd/A)” was calculated. In addition, the time until the luminance value measured by the luminance measuring device gradually decreased to 95% of the initial luminance was defined as "LT95 life (hrs)".

The evaluation results are shown in Table 1 below.

(Example 4, Comparative Examples 3-4)
An organic EL device was produced and evaluated in the same manner as in Example 1, except that the host compound in the light-emitting layer was changed to the configuration shown in Table 2 below. The evaluation results are shown in Table 2 below.

(Example 5, Comparative Examples 5-6)
An organic EL device was produced and evaluated in the same manner as in Example 1, except that the host compound in the light-emitting layer was changed to the configuration shown in Table 3 below. The evaluation results are shown in Table 3 below.

(Examples 6 to 17)
An organic EL device was produced and evaluated in the same manner as in Example 1, except that the host compound in the light-emitting layer was changed to the configuration shown in Table 4 below. The evaluation results are shown in Table 3 below.

(Examples 18-24)
An organic EL device was produced and evaluated in the same manner as in Example 1, except that the host compound of the light emitting layer was changed to the configuration shown in Table 5 below and the dopant material was changed to a platinum complex represented by the following chemical formula. bottom. The evaluation results are shown in Table 5 below.

(Example 25, Comparative Examples 7-8)
Example except that the host compound of the light-emitting layer was changed to the configuration shown in Table 6 below, and the dopant material was changed to a red phosphorescent light-emitting complex (Ir(piq) ₂ (acac)) represented by the following chemical formula. An organic EL device was produced in the same manner as in Example 1. Performance evaluation was performed under the condition of luminance of 2000 nit. The evaluation results are shown in Table 6 below.

(Example 26, Comparative Example 9)
An organic An EL device was produced. Performance evaluation was performed under the condition of a luminance of 1000 nit, and the lifetime was evaluated by the time (LT70 lifetime (hrs)) until the luminance reached 70% of the initial luminance. The evaluation results are shown in Table 7 below.

(Example 27, Comparative Examples 10-11)
An organic An EL device was produced. Performance evaluation was performed under the condition of a luminance of 1000 nit. The evaluation results are shown in Table 8 below.

From Tables 1 to 8 above, the organic EL devices of Examples using the three types of host compounds according to the present embodiment exhibit current efficiencies (luminous efficiencies) that are substantially equal to or higher than those of the organic EL devices of Comparative Examples. , and the luminescence lifetime was greatly improved. In addition, the organic EL devices of Examples exhibited good film-forming properties. Therefore, it was found that the host compound according to the present invention is useful as an organic EL device material for the coating method.

Moreover, the host compounds used in the examples are preferable from the viewpoint of mass production because they can form the light-emitting layer of the organic EL device by a coating method.

As described above, the present invention has been described with reference to embodiments and examples, but the present invention is not limited to specific embodiments and examples, and various can be modified and changed.

100 organic electroluminescence device (organic EL device),
110 substrate,
120 first electrode,
130 hole injection layer,
140 hole transport layer,
150 light emitting layer,
160 electron transport layer,
170 electron injection layer,
180 second electrode;

Claims (4)

An organic electroluminescent element having a light-emitting layer between a pair of electrodes,
The light-emitting layer is
at least one electron-transporting compound;
at least one hole-transporting compound;
at least one wide-gap compound having a HOMO-LUMO energy gap of 3.3 eV or more;
including
The electron-transporting compound is a compound selected from the following compound group (1), the hole-transporting compound is a compound selected from the following compound group (2), and the wide gap compound is the following compound group (3) an organic electroluminescent device, which is a compound selected from:

Ar in the above compound group (1) and compound group (2) is each independently a substituted or unsubstituted aryl group or a substituted or unsubstituted heteroaryl group:

In the above compound group (3),
each Ar ₂ is independently a phenyl group, a hydrocarbon ring assembly group in which a plurality of aromatic hydrocarbon rings are directly bonded via a single bond, or a substituted or unsubstituted heteroaryl group;
each Ar ₃ is independently a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group, or a substituted or unsubstituted heteroaryl group;
Ar ₄ is a hydrogen atom, a substituted or unsubstituted aryl group, or a substituted or unsubstituted heteroaryl group. 2. The organic electroluminescence device according to claim 1, wherein the content of said hole-transporting compound in said light-emitting layer is more than 25% by mass. 3. The organic electroluminescence device according to claim 1, wherein said light-emitting layer contains a fluorescent compound or a phosphorescent compound. at least one electron-transporting compound;
at least one hole-transporting compound;
at least one wide-gap compound having a HOMO-LUMO energy gap of 3.3 eV or more;
a solvent;
A method for producing an organic electroluminescence device according to any one of claims 1 to 3, comprising applying a composition containing
The electron-transporting compound is a compound selected from the following compound group (1), the hole-transporting compound is a compound selected from the following compound group (2), and the wide gap compound is the following compound group (3) A method for producing an organic electroluminescent device, which is a compound selected from:

Ar in the above compound group (1) and compound group (2) is each independently a substituted or unsubstituted aryl group or a substituted or unsubstituted heteroaryl group:

In the above compound group (3),
each Ar ₂ is independently a phenyl group, a hydrocarbon ring assembly group in which a plurality of aromatic hydrocarbon rings are directly bonded via a single bond, or a substituted or unsubstituted heteroaryl group;
each Ar ₃ is independently a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group, or a substituted or unsubstituted heteroaryl group;
Ar ₄ is a hydrogen atom, a substituted or unsubstituted aryl group, or a substituted or unsubstituted heteroaryl group.

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