WO2013190620A1

WO2013190620A1 - Organic electroluminescence element

Info

Publication number: WO2013190620A1
Application number: PCT/JP2012/065534
Authority: WO
Inventors: 黒田　和男; 秀雄工藤; 浩大畑; 敏治内田
Original assignee: パイオニア株式会社
Priority date: 2012-06-18
Filing date: 2012-06-18
Publication date: 2013-12-27

Abstract

An organic electroluminescence element including an organic layer including a light-emitting layer sandwiched between a light-transmitting electrode layer and a reflective metal electrode layer. The reflective metal electrode layer has, laminated in order from the organic layer side, a conductive film, a light-transmitting dielectric film, and a reflective metal film. The light-transmitting dielectric film has at least the same refractive index as the organic layer. At least part of the reflective metal film is electrically connected to the conductive film.

Description

Organic electroluminescence device

The present invention relates to an organic electroluminescence element.

2. Description of the Related Art An organic electroluminescence element (hereinafter referred to as an organic EL element) in which an organic layer including a light emitting layer is sandwiched between an anode electrode layer and a cathode electrode layer on a transparent glass substrate is known. In this organic EL element, when a voltage is applied between the anode and the cathode, the light emitting layer emits light. The emitted light is extracted through the anode and the glass substrate by making the anode transparent. However, since the light emitted from the light emitting layer is confined and extinguished by total reflection between the anode-glass interface and between the glass-air interface, only about 20% of the light generated in the light emitting layer is emitted. It cannot be taken out. Therefore, for this problem, for example, in an organic EL element in which an organic light emitting layer is provided between two transparent electrodes on a transparent substrate, a high refractive index layer and a mirror layer are provided on the opposite transparent electrode on the light extraction side. A structure for reducing waveguide loss by stacking has been proposed (see, for example, Patent Document 1).

JP 2011-233288 A

Patent Document 1 suggests that the high refractive index layer in the organic EL element makes it difficult for light emitted from the light emitting layer to be coupled to the plasmon mode. However, when total reflection occurs in the mirror layer, plasmon loss occurs at a predetermined angle. Moreover, in the organic EL element of Patent Document 1, since, for example, a colored inorganic oxide is used for the high refractive index layer, attenuation scattering occurs in the colored high refractive index layer. Further, Patent Document 1 recommends the use of a dielectric multilayer film in addition to metal as a mirror layer. However, in this case, the light extraction efficiency cannot be sufficiently increased because the reflectance varies depending on the incident angle of light on the dielectric multilayer film. Furthermore, high reflectivity can be expected even with a dielectric multilayer film, but when the angle dependency is high and light emission in all directions is required like illumination, the dielectric multilayer film is not suitable as a mirror layer.

The present invention has been made in view of the above points, and an object thereof is to provide an organic electroluminescence element capable of improving light extraction efficiency.

The organic electroluminescence device of the present invention is an organic electroluminescence device comprising an organic layer sandwiched between a translucent electrode layer and a reflective metal electrode layer and comprising a light emitting layer,
The reflective metal electrode layer includes a translucent conductive film in contact with the organic layer, a translucent dielectric film in contact with the conductive film and having a refractive index equal to or greater than a refractive index of the organic layer, A reflective metal film in contact with the translucent dielectric film, wherein at least a part of the reflective metal film is electrically connected to the conductive film.

FIG. 1 is a schematic cross-sectional view schematically showing a configuration of an organic EL element which is an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view schematically showing a laminated structure of the organic EL element shown in FIG. FIG. 3 is a partial cross-sectional view of an organic EL device according to another embodiment of the present invention. FIG. 4 is a partially cutaway perspective view schematically showing a configuration of an organic EL element which is another embodiment of the present invention. FIG. 5 is a partial cross-sectional view of an organic EL device according to another embodiment of the present invention. FIG. 6 is a partial cross-sectional view of an organic EL device according to another embodiment of the present invention. FIG. 7 is a partially cutaway perspective view showing a reflective metal electrode layer of an organic EL device according to another embodiment of the present invention. FIG. 8 is a partially cutaway perspective view showing a reflective metal electrode layer of an organic EL device according to another embodiment of the present invention. FIG. 9 is a partially cutaway perspective view showing a reflective metal electrode layer of an organic EL device according to another embodiment of the present invention. FIG. 10 is a perspective view showing a part of a divided translucent dielectric film of an organic EL element according to another embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

As shown in FIG. 1, an organic EL element according to an embodiment of the present invention includes a translucent electrode layer 2, an organic layer 3, a conductive film CF, a reflective metal film 4, and a translucent substrate on a translucent substrate 1. The conductive dielectric films TF are sequentially stacked. The translucent conductive film CF, the translucent dielectric film TF, and the reflective metal film 4 in contact with the organic layer 3 constitute a reflective metal electrode layer as a composite electrode. The conductive film CF functions as a cathode, the reflective metal film 4 functions as a reflection part, and the translucent dielectric film TF functions as a relay part.

As shown in FIG. 1, the reflective metal film 4 sandwiches the translucent dielectric film TF together with the conductive film CF, and is further electrically connected to the conductive film CF at the connection portion around the light emitting region. . As a result, an electric field can be applied to the organic layer 3 from a distance close to the conductive film CF, and at the same time, the plasmon loss is reduced because the conductive film CF is a thin film. Since the conductive film CF is connected to the reflective metal film 4 which is away from the organic layer 3 and is thick and has a small electric resistance, a voltage drop in the conductive film can be suppressed.

Although the reflective metal film 4 is not limited, for example, a metal such as aluminum, silver, copper, nickel, chromium, gold, or platinum is used. In addition, these materials may be used only by 1 type and may use 2 or more types together by arbitrary combinations and a ratio.

The translucent material constituting the translucent dielectric film TF sandwiched between the conductive film CF and the reflective metal film 4 has a refractive index of the organic layer 3, particularly the organic layer in contact with the conductive film CF. Is selected from organic materials equivalent to or better than For example, the translucent dielectric film TF is made of a hole transporting compound. The translucent dielectric film TF made of a hole transporting compound functions as a layer that blocks electron transfer because the hole transporting compound is a material that does not flow electrons. The translucent dielectric film TF can prevent electrons from flowing into the reflective metal film 4 to become a cathode, and can increase luminous efficiency.

In the present specification, “equivalent refractive index” means that the difference between one refractive index and the other refractive index is less than 0.3, preferably 0.2 or less, particularly preferably 0.1 or less. That means. Further, the refractive index “low” or “high” may be “low” or “high” to such an extent that a difference in measurement occurs, but in practice, it exceeds 0.1, preferably exceeds 0.2. More preferably 0.3 or more, still more preferably 0.4 or more, particularly preferably 0.5 or more, indicating a low or high difference.

As shown in FIG. 2, the organic layer 3 sandwiched between the translucent electrode layer 2 and the reflective metal electrode layer is composed of a hole injection layer 3a, a hole transport layer 3b, a light emitting layer 3c, an electron stacked in order. A transport layer 3d and an electron injection layer 3e. The organic layer 3 is a light-emitting laminated body, and is not limited to these laminated structures, and may have a laminated structure including at least a light-emitting layer or a charge transport layer that can also be used. The organic layer 3 may be configured by omitting the hole transport layer 3b, the hole injection layer 3a, or the hole injection layer 3a and the electron transport layer 3d from the stacked structure. May be.

Known methods for forming the organic layer 3 include dry coating methods such as sputtering and vacuum deposition, and wet coating methods such as screen printing, spraying, ink jetting, spin coating, gravure printing, and roll coater. ing. For example, the hole injection layer, the hole transport layer, and the light emitting layer are uniformly formed as a solid film by a wet coating method, and the electron transport layer and the electron injection layer are uniformly formed sequentially as a solid film by a dry coating method. A film may be formed. Alternatively, all the functional layers may be uniformly and sequentially formed as a solid film by a wet coating method.

The anode translucent electrode layer 2 for supplying holes to the functional layers up to the light emitting layer 3c is made of ITO (Indium-tin-oxide), ZnO, ZnO—Al ₂ O ₃ (so-called AZO), In ₂ O _3. It can be composed of —ZnO (so-called IZO), SnO ₂ —Sb ₂ O ₃ (so-called ATO), RuO ₂ or the like. Furthermore, for the translucent electrode layer 2, it is preferable to select a material having a transmittance of at least 10% at the emission wavelength obtained from the organic EL material.

The translucent electrode layer 2 usually has a single-layer structure, but it can also have a laminated structure made of a plurality of materials if desired.

The material of the cathode conductive film CF that supplies electrons to the functional layers up to the light emitting layer 3c preferably contains a metal having a low work function in order to perform electron injection efficiently. For example, tin, magnesium, indium A suitable metal such as calcium, aluminum, silver, or an alloy thereof is used. Specific examples include low work function alloy electrodes such as magnesium-silver alloy, magnesium-indium alloy, and aluminum-lithium alloy. In addition, only 1 type may be used for the material of conductive film CF, and 2 or more types may be used together by arbitrary combinations and ratios.

The conductive film CF is a metal thin film made of an electric conductor having an electric conductivity of 10 ⁶ S / m or more and having a transmittance of 50% or more in the visible light wavelength band. The material of the conductive film CF includes, in addition to metals, carbon such as graphite and graphene having electrical conductivity. The silver thin film with a thickness of 20 nm of the conductive film CF has a transmittance of 50%. An Al film having a thickness of 10 nm as the metal thin film has a transmittance of 50%. The 20 nm-thick MgAg alloy film as the metal thin film has a transmittance of 50%. When the conductive film CF is formed of a metal thin film, the conductivity can be ensured if the lower limit of the film thickness is 5 nm.

The conductive film CF is formed on the organic layer 3 by sputtering or vacuum deposition.

Since the organic layer 3 is sandwiched between and in contact with the translucent electrode layer 2 and the conductive film CF, a driving voltage is applied to the organic layer 3 through the translucent electrode layer 2 and the conductive film CF. Thus, the light generated in the light emitting layer 3c in the organic layer 3 passes through the translucent electrode layer 2 and is further reflected by the reflective metal film 4 through the conductive film CF. It passes through and is taken out from the surface of the translucent substrate 1.

[Functional layer of organic layer 3]
[Hole injection layer]
The hole injection layer 3a is preferably a layer containing an electron accepting compound (so-called hole transporting compound).

When forming by a wet coating method, the composition for forming a hole injection layer usually contains a hole transporting compound and a solvent as a constituent material of the hole injection layer. Examples of the solvent include, but are not limited to, ether solvents, ester solvents, aromatic hydrocarbon solvents, amide solvents, and the like. Examples of ether solvents include aliphatic ethers such as ethylene glycol dimethyl ether, ethylene glycol diethyl ether, propylene glycol monomethyl ether acetate (so-called PGMEA), 1,2-dimethoxybenzene, 1,3-dimethoxybenzene, anisole, and phenetole. , Aromatic ethers such as 2-methoxytoluene, 3-methoxytoluene, 4-methoxytoluene, 2,3-dimethylanisole, and 2,4-dimethylanisole.

Examples of the ester solvent include aromatic esters such as phenyl acetate, phenyl propionate, methyl benzoate, ethyl benzoate, propyl benzoate, and n-butyl benzoate.

Examples of the aromatic hydrocarbon solvent include toluene, xylene, cyclohexylbenzene, 3- isopropylpropylphenyl, 1,2,3,4-tetramethylbenzene, 1,4-diisopropylbenzene, cyclohexylbenzene, methylnaphthalene and the like. Can be mentioned.

Examples of the amide solvent include N, N-dimethylformamide and N, N-dimethylacetamide. In addition, dimethyl sulfoxide and the like can also be used. These solvent may use only 1 type and may use 2 or more types by arbitrary combinations and a ratio.

The hole transporting compound may be a polymer compound such as a polymer or a low molecular compound such as a monomer, but is preferably a low molecular compound.

The hole transporting compound is preferably a compound having an ionization potential of 4.5 eV to 6.0 eV from the viewpoint of a charge injection barrier from the anode to the hole injection layer. Examples of hole transporting compounds include aromatic amine derivatives, phthalocyanine derivatives represented by phthalocyanine copper (so-called CuPc), porphyrin derivatives, oligothiophene derivatives, polythiophene derivatives, benzylphenyl derivatives, tertiary amines with fluorene groups. Examples include linked compounds, hydrazone derivatives, silazane derivatives, silanamine derivatives, phosphamine derivatives, quinacridone derivatives, polyaniline derivatives, polypyrrole derivatives, polyphenylene vinylene derivatives, polythienylene vinylene derivatives, polyquinoline derivatives, polyquinoxaline derivatives, and carbon. Here, the derivative includes, for example, an aromatic amine derivative, and includes an aromatic amine itself and a compound having an aromatic amine as a main skeleton. There may be.

As the hole transporting compound, a conductive polymer obtained by polymerizing 3,4-ethylenedioxythiophene, which is a polythiophene derivative, in high molecular weight polystyrene sulfonic acid (so-called PEDOT / PSS) is also preferable. Furthermore, the end of the polymer of PEDOT / PSS may be capped with methacrylate or the like.

The hole transporting compound used as the material for the hole injection layer may contain any one of these compounds alone, or may contain two or more. In the case of containing two or more kinds of hole transporting compounds, the combination is arbitrary, but one or more kinds of aromatic tertiary amine polymer compounds and one or two kinds of other hole transporting compounds. The above can also be used together. From the viewpoints of amorphousness and visible light transmittance, an aromatic amine compound is preferable for the hole injection layer, and an aromatic tertiary amine compound is particularly preferable. Here, the aromatic tertiary amine compound is a compound having an aromatic tertiary amine structure, and includes a compound having a group derived from an aromatic tertiary amine.

The concentration of the hole transporting compound in the composition for forming a hole injection layer is usually 0.01% by weight or more, preferably 0.1% by weight or more, and more preferably 0.00% by weight in terms of film thickness uniformity. 5% by weight or more, usually 70% by weight or less, preferably 60% by weight or less, more preferably 50% by weight or less. If this concentration is too high, film thickness unevenness may occur, and if it is too low, defects may occur in the formed hole injection layer.

In addition to the electron-accepting compound, the composition for forming a hole injection layer may further contain other components. Examples of other components include various organic EL materials, binder resins, coatability improvers, and the like. In addition, only 1 type may be used for another component and it may use 2 or more types together by arbitrary combinations and ratios.

When forming a hole injection layer by a wet coating method, usually, a material for forming the hole injection layer is mixed with an appropriate solvent to prepare a film-forming composition, and this hole injection layer forming composition The hole injection layer is formed by applying the material onto the anode by an appropriate technique, forming a film, and drying.

The film thickness of the hole injection layer is usually 5 nm or more, preferably 10 nm or more, and usually 1000 nm or less, preferably 500 nm or less.

[Hole transport layer]
The material of the hole transport layer 3b may be any material that has been conventionally used as a constituent material of the hole transport layer. For example, it is exemplified as the hole transport compound used in the above-described hole injection layer. Things. In addition, arylamine derivatives, fluorene derivatives, spiro derivatives, carbazole derivatives, pyridine derivatives, pyrazine derivatives, pyrimidine derivatives, triazine derivatives, quinoline derivatives, phenanthroline derivatives, phthalocyanine derivatives, porphyrin derivatives, silole derivatives, oligothiophene derivatives, condensed polycyclic aromatics Group derivatives, metal complexes and the like. Also, for example, polyvinylcarbazole derivatives, polyarylamine derivatives, polyvinyltriphenylamine derivatives, polyfluorene derivatives, polyarylene derivatives, polyarylene ether sulfone derivatives containing tetraphenylbenzidine, polyarylene vinylene derivatives, polysiloxane derivatives, polythiophenes Derivatives, poly (p-phenylene vinylene) derivatives, and the like. These may be any of an alternating copolymer, a random polymer, a block polymer, or a graft copolymer. Further, it may be a polymer having a branched main chain and three or more terminal portions, or a so-called dendrimer.

When the hole transport layer is formed by a wet coating method, a composition for forming a hole transport layer is prepared in the same manner as the formation of the hole injection layer, and then dried after wet film formation.

In addition to the hole transporting compound, the hole transporting layer forming composition contains a solvent. The solvent used is the same as that used for the composition for forming the hole injection layer. The film forming conditions, the drying conditions, and the like are the same as in the case of forming the hole injection layer.

The hole transport layer may contain various organic EL materials, a binder resin, a coating property improving agent and the like in addition to the hole transporting compound.

The film thickness of the hole transport layer is usually 5 nm or more, preferably 10 nm or more, and usually 300 nm or less, preferably 100 nm or less.

As described above, since at least the hole injection layer 3a or the hole transport layer 3b is preferably applied thick, the film thickness of the hole injection layer 3a and / or the hole transport layer 3b from the anode 2 to the light emitting layer 3c. Is preferably at least 100 nm.

[Light emitting layer]
The light emitting layer 3c may be a red, green and blue light emitting independent light emitting layer or a mixed light emitting layer thereof, a compound having a property of transporting holes (hole transporting compound), or A compound having an electron transporting property (electron transporting compound) can also be contained. An organic EL material may be used as a dopant material, and a hole transporting compound, an electron transporting compound, or the like may be appropriately used as a host material. There is no particular limitation on the organic EL material, and a substance that emits light at a desired emission wavelength and has good emission efficiency may be used.

Any known material can be applied as the organic EL material. For example, it may be a fluorescent material or a phosphorescent material, but it is preferable to use a phosphorescent material from the viewpoint of internal quantum efficiency. The light emitting layer may have a single layer structure or a multilayer structure made of a plurality of materials as desired. For example, a fluorescent material may be used for the blue light emitting layer, and a phosphorescent material may be used for the green and red light emitting layers. Further, a diffusion preventing layer can be provided between the light emitting layers.

Examples of fluorescent materials (blue fluorescent dyes) that emit blue light include naphthalene, perylene, pyrene, chrysene, anthracene, coumarin, p-bis (2-phenylethenyl) benzene, and derivatives thereof.

Examples of the fluorescent material (green fluorescent dye) that emits green light include aluminum complexes such as quinacridone derivatives, coumarin derivatives, and Alq3 (tris (8-hydroxy-quinoline) aluminum).

Examples of fluorescent materials that give yellow light emission (yellow fluorescent dyes) include rubrene and perimidone derivatives.

Examples of fluorescent materials that give red light emission (red fluorescent dyes) include DCM (4- (dicyanomethylene) -2-methyl-6- (p-dimethylaminostyryl) -4H-pyran) compounds, benzopyran derivatives, rhodamine derivatives, benzoates. Examples thereof include thioxanthene derivatives and azabenzothioxanthene.

The phosphorescent material is selected from, for example, the long-period periodic table (hereinafter referred to as the long-period periodic table when referring to “periodic table” unless otherwise specified). An organometallic complex containing a metal can be given. Preferred examples of the metal selected from Groups 7 to 11 of the periodic table include ruthenium, rhodium, palladium, silver, rhenium, osmium, iridium, platinum, and gold. As the ligand of the complex, a ligand in which a (hetero) aryl group such as a (hetero) arylpyridine ligand or a (hetero) arylpyrazole ligand and a pyridine, pyrazole, phenanthroline, or the like is connected is preferable. A pyridine ligand and a phenylpyrazole ligand are preferable. Here, (hetero) aryl represents an aryl group or a heteroaryl group.

Specific examples of phosphorescent materials include tris (2-phenylpyridine) iridium (so-called Ir (ppy) 3), tris (2-phenylpyridine) ruthenium, tris (2-phenylpyridine) palladium, and bis (2-phenyl). Pyridine) platinum, tris (2-phenylpyridine) osmium, tris (2-phenylpyridine) rhenium, octaethylplatinum porphyrin, octaphenylplatinum porphyrin, octaethyl palladium porphyrin, octaphenyl palladium porphyrin, and the like.

The molecular weight of the compound used as the organic EL material is usually 10,000 or less, preferably 5000 or less, more preferably 4000 or less, still more preferably 3000 or less, and usually 100 or more, preferably 200 or more, more preferably 300 or more, still more preferably. Is in the range of 400 or more. If the molecular weight of the organic EL material is too small, the heat resistance will be significantly reduced, gas generation will be caused, the film quality will be deteriorated when the film is formed, or the morphology of the functional layer will be changed due to migration, etc. There is a case. On the other hand, if the molecular weight of the organic EL material is too large, it tends to be difficult to purify the organic compound, or it may take time to dissolve the organic EL material in a solvent when formed by a wet coating method.

In addition, only 1 type may be used for an organic EL material, and 2 or more types may be used together by arbitrary combinations and a ratio. The proportion of the organic EL material in the light emitting layer is usually 0.05% by weight or more and usually 35% by weight or less. If the amount of the organic EL material is too small, uneven light emission may occur, and if the amount is too large, the light emission efficiency may be reduced. In addition, when using together 2 or more types of organic EL material, it is made for the total content of these to be contained in the said range. The component having the highest content in the light emitting layer is called a host material, and the component having a smaller content is called a guest material.

The light emitting layer may contain a hole transporting compound as a constituent material. Here, among the hole transporting compounds, examples of the low molecular weight hole transporting compound include various compounds exemplified as the hole transporting compound in the hole injection layer 3a described above, for example, Two or more condensed aromatic rings containing two or more tertiary amines represented by 4′-bis [N- (1-naphthyl) -N-phenylamino] biphenyl (so-called NPB) are attached to the nitrogen atom. Substituted aromatic diamines, aromatic amine compounds having a starburst structure such as 4,4 ′, 4 ″ -tris (1-naphthylphenylamino) triphenylamine, and aromatics composed of tetramers of triphenylamine And spiro compounds such as 2,2 ′, 7,7′-tetrakis- (diphenylamino) -9,9′-spirobifluorene.

In addition, in a light emitting layer, only 1 type may be used for a hole transportable compound, and it may use 2 or more types together by arbitrary combinations and a ratio.

The proportion of the hole transporting compound in the light emitting layer is usually 0.1% by weight or more and usually 65% by weight or less. If the amount of the hole transporting compound is too small, it may be easily affected by a short circuit, and if it is too large, the film thickness may be uneven. In addition, when using together 2 or more types of hole transportable compounds, it is made for the total content of these to be contained in the said range.

The light emitting layer may contain an electron transporting compound as a constituent material. Here, among the electron transporting compounds, examples of low molecular weight electron transporting compounds include 2,5-bis (1-naphthyl) -1,3,4-oxadiazole (so-called BND), 2 , 5-bis (6 ′-(2 ′, 2 ″ -bipyridyl))-1,1-dimethyl-3,4-diphenylsilole (so-called PyPySPyPy), bathophenanthroline (so-called BPhen), 2,9 -Dimethyl-4,7-diphenyl-1,10-phenanthroline (so-called BCP, bathocuproin), 2- (4-biphenylyl) -5- (p-tertiarybutylphenyl) -1,3,4-oxadiazole (So-called tBu-PBD), 4,4′-bis (9H-carbazol-9-yl) biphenyl (so-called CBP), etc. In the light-emitting layer, an electron-transporting compound is included. , It may be used alone, or as a combination of two or more kinds in any combination and in any ratio.

The proportion of the electron transporting compound in the light emitting layer is usually 0.1% by weight or more and usually 65% by weight or less. If the amount of the electron transporting compound is too small, it may be easily affected by a short circuit, and if it is too large, the film thickness may be uneven. In addition, when using together 2 or more types of electron transport compounds, it is made for the total content of these to be contained in the said range.

In the case of forming by a wet coating method, the light emitting layer is prepared by dissolving the above light emitting layer material in an appropriate solvent to prepare a composition for forming a light emitting layer. Is formed. Therefore, in the case of forming by a wet coating method, the light emitting layer coating solution is prepared by dispersing or dissolving at least two kinds of solid contents (host material and guest material) to be the light emitting layer as a solute in a solvent. The solvent to be used can be selected from the solvents that can be used for the composition for forming a hole injection layer.

The ratio of the light emitting layer solvent to the light emitting layer forming composition for forming the light emitting layer is usually 0.01% by weight or more and usually 70% by weight or less. In addition, when using 2 or more types of solvents mixed as a solvent for light emitting layers, it is made for the sum total of these solvents to satisfy | fill this range.

The film thickness of the light emitting layer is usually 3 nm or more, preferably 5 nm or more, and usually 200 nm or less, preferably 100 nm or less. If the light emitting layer is too thin, defects may occur in the film, and if it is too thick, the driving voltage may increase.

[Electron transport layer]
The electron transport layer 3d is provided for the purpose of further improving the light emission efficiency of the organic EL element, and efficiently transports electrons injected from the cathode between the electrodes to which an electric field is applied in the direction of the light emitting layer. It is formed from an electron transporting compound capable of forming

As the electron transporting compound used for the electron transporting layer, usually, the electron injection efficiency from the cathode conductive film CF or the electron injection layer 3e is high, and the injected electrons with high electron mobility are efficiently used. A compound that can be transported is used. Examples of compounds that satisfy such conditions include metal complexes of Alq3 and 10-hydroxybenzo [h] quinoline, oxadiazole derivatives, distyrylbiphenyl derivatives, silole derivatives, 3-hydroxyflavone metal complexes, and 5-hydroxyflavones. Metal complex, benzoxazole metal complex, benzothiazole metal complex, trisbenzimidazolylbenzene, quinoxaline compound, phenanthroline derivative, 2-t-butyl-9,10-N, N′-dicyanoanthraquinonediimine, n-type hydrogenated amorphous Quality silicon carbide, n-type zinc sulfide, n-type zinc selenide and the like.

In addition, only 1 type may be used for the material of an electron carrying layer, and 2 or more types may be used together by arbitrary combinations and a ratio.

The formation method of the electron transport layer is not limited, and can be formed by a wet coating method or a dry coating method. In the case of forming by a wet coating method, the electron transport layer is prepared by dissolving the electron transport layer material in an appropriate solvent to prepare a composition for forming an electron transport layer. It is formed by removing. The solvent to be used can be selected from the solvents that can be used for the composition for forming a hole injection layer.

The film thickness of the electron transport layer is usually 1 nm or more, preferably 5 nm or more, and usually 300 nm or less, preferably 100 nm or less.

[Electron injection layer]
The electron injection layer 3e plays a role of efficiently injecting electrons injected from the cathode into the electron transport layer and the light emitting layer. For example, the electron injection layer 3e includes organic electron transport compounds represented by metal complexes such as nitrogen-containing heterocyclic compounds such as bathophenanthroline and aluminum complexes of 8-hydroxyquinoline. Further, the electron injection efficiency can be increased by doping the electron injection layer 3e of the organic electron transport compound with an electron donating material. Examples of the electron donating material include alkali metals such as sodium and cesium, alkaline earth metals such as barium and calcium, compounds thereof (CsF, Cs ₂ CO ₃ , Li ₂ O, LiF), sodium, Alkali metals such as potassium, cesium, lithium and rubidium are used. The thickness of the electron injection layer 3e is usually 5 nm or more, preferably 10 nm or more, and is usually 200 nm or less, preferably 100 nm or less.

The formation method of the electron injection layer is not limited, and can be formed by a wet coating method or a dry coating method. In the case of forming by a wet coating method, the electron injection layer is prepared by dissolving the electron injection layer material in a suitable solvent to prepare a composition for forming an electron injection layer. It is formed by removing. The solvent to be used can be selected from the solvents that can be used for the composition for forming a hole injection layer.

The operation of the organic EL element will be described with reference to FIG. 3 in the case where a light emitting material having an emission spectrum having a central peak wavelength (hereinafter referred to as λ) of 560 nm is used for the light emitting layer 3c.

In this embodiment, the distance between the light emitting point and the reflective metal film 4 is optically set to 3 times (odd times) of λ / 4. That is, in the light emitting layer 3c, the optical distance from the conductive film CF is 1/4 of the emission peak wavelength of the light emitting layer 3c, and the optical distance from the reflective metal film 4 is the light emission of the light emitting layer 3c. It has a light emitting surface which is an odd multiple of 3 times or more of 1/4 of the peak wavelength. The conductive film CF functioning as a cathode for applying a strong electric field is disposed at a position closer to the light emitting layer 3 c than the reflective metal film 4.

The distance between the light emitting point of the light emitting layer 3c and the conductive film CF is optically set to λ / 4. This is a value that takes into account thin-film interference, and utilizes the property that when reflected by the reflective metal film 4, a phase difference of π occurs in the round trip in the optical path length, and the π phase changes in metal reflection. The phase can be the same as the phase of the light traveling from the point toward the extraction layer.

Since the minimum diameter of light is the wavelength size, the diameter of the energy distribution of light at the minimum emission point can be 560 nm. If the average refractive index of the organic layer including the light emitting layer is 1.8, the energy distribution is physically within the distance range of 560 / 1.8 = 311 nm (radius 155.5 nm).

In FIG. 3, when the circle shown by the broken line having a radius of 155.5 nm is overlapped from the light emitting point, the end of energy is located in the middle of the translucent dielectric film TF with the conductive film CF interposed therebetween, and the reflective metal film 4 Not reached. That is, it is preferable that the reflective metal film 4 is disposed at a position separated from the light emitting surface by a half wavelength or more of the light emission peak wavelength of the light emitting layer 3c.

Since the refractive index of the conductive film CF on the light emitting layer side and the outer translucent dielectric film T side is equal to or greater than that, the total reflection condition is not satisfied at all angles within the circle indicated by the broken line, and evanescent light is not generated. Neither plasmon resonance occurs.

The evanescent light oozes from the high refractive index side to the low refractive index side at the time of total reflection, and the evanescent light oozed from the low refractive index layer with a thin film (thickness below wavelength) has a high refractive index on the outside. It has the property of returning to the original light. Further, the surface plasmon generated by the evanescent light and the light incident from a predetermined angle resonates (plasmon resonance), resulting in a plasmon loss, and the level of the reflected light rapidly decreases. However, no evanescent light is generated in this embodiment.

In FIG. 3, since the upward light L1 has the same phase as the light reflected by the reflective metal film 4, it is strengthened and output from the glass substrate 1.

In FIG. 3, when the lateral light L2 is emitted, it exists in the energy distribution, but does not satisfy the total reflection condition.

In FIG. 3, light L3 within an obliquely upward critical angle passes through the hole transport layer 3b, the hole injection layer 3a, and the translucent electrode layer 2 as it is. Light L4 having a critical angle or more at the interface between the translucent electrode layer 2 and the glass substrate proceeds while repeatedly attenuated total reflection.

In FIG. 3, obliquely lower light L5 crosses the conductive film CF at the time of light emission. The light travels as it is and reaches the reflective metal film 4. Also in this case, evanescent light is not generated and plasmon resonance does not occur.

In FIG. 3, the downward light L6 does not generate evanescent light, and is reflected by the reflective metal film 4 so that the optical path length is λ / 4. Further, because of the metal reflection at the reflective metal film 4, the phase is further shifted by π, and eventually the light has the same phase as the emitted light. Therefore, because the phase is the same as that of the upward light, they are output in an intensified manner.

When reflecting, if the reflective metal film 4 is thin and the refractive index outside the reflective metal film 4 is lower than the inside, total reflection is performed at a critical angle or more. Evanescent light is also generated to excite surface plasmons, plasmon resonance occurs at a predetermined angle, and plasmon loss occurs.

However, since the thickness of the reflective metal film 4 is increased to about 200 nm in this embodiment, the evanescent light does not ooze out to the outside and is a metal reflection.

As described above, the conductive film CF is disposed at a position close to the light emitting layer 3c, that is, λ / 4, the relatively thick reflective metal film 4 is disposed at 3 × λ / 4, and the conductive film CF and the reflective metal film 4 are disposed. And a translucent dielectric film TF having a refractive index equal to or higher than that of the organic layer is provided between the conductive film CF and the reflective metal film 4, thereby reducing loss during light emission and plasmon loss. The effect which suppresses can be acquired. In the description, although the refractive index of the conductive film CF is ignored in the description as a model, it is necessary to consider the refractive index of the conductive film to be used when actually creating the film.

[Modification]
FIG. 4 shows a modification of the organic EL element as another embodiment. In addition, since the component shown with the same code | symbol as the said Example is the same as that of the organic EL element of the said Example, those description is abbreviate | omitted. In the above-described embodiment, the connection portion that contacts the conductive film CF is provided at the edge of the reflective metal film 4, but the reflective metal film 4 penetrates the translucent dielectric film TF in the light emitting region as the connection portion. Thus, it can be configured to have at least one protrusion in contact with the conductive film CF.

The organic EL element of the modification shown in FIG. 4 has a plurality of protrusions that penetrate the translucent dielectric film TF and contact the conductive film CF, each of which is electrically connected from the reflective metal film 4 to the conductive film CF. Conductor connection portion 4a. Each conductor connection portion 4 a is a plate made of the same material as the reflective metal film 4, and they are formed on the reflective metal film 4 in a frame shape. Each of the divided translucent dielectric films TF shown in FIG. 4 has a rectangular parallelepiped shape. The translucent dielectric film TF divided by the conductor connection portion 4a is provided in a matrix so that each is surrounded by the reflective metal film 4, the conductor connection portion 4a, and the conductive film CF. By connecting the reflective metal film 4 and the conductive film CF with the plurality of conductor connection portions 4a, electrons can be injected into the organic layer 3 more uniformly. Since the plurality of conductor connecting portions 4a extend in the thickness direction of the translucent dielectric film TF between the conductive film CF and the reflective metal film 4 and both surfaces act as reflecting surfaces, the light extraction efficiency is improved. It is preferable.

The plurality of translucent dielectric films TF divided by the conductor connection portion 4a have substantially the same rectangular parallelepiped shape, but are substantially uniform on a flat interface (XY plane) with the conductive film CF. It may be arranged with a high distribution density and may be arranged periodically, and the period is preferably sufficiently larger than the wavelength of light generated in the organic layer 3.

5 and 6 show further modifications of the organic EL element as another embodiment. In addition, since the component shown with the same code | symbol as the Example shown in FIG. 4 is the same as that of the organic EL element of the said Example, those description is abbreviate | omitted.

The organic EL element of the modification shown in FIG.5 and FIG.6 is provided with the reflective inclination part 4b which gave the inclination angle from now on the reflective metal film 4 of the cell enclosed by the conductor connection part 4a. Thereby, a concave mirror can be comprised for every cell enclosed by the conductor connection part 4a. By providing the organic EL element with the reflective inclined portion 4b on the reflective metal film 4 between adjacent conductor connection portions 4a, the light extraction efficiency to the substrate side is improved. 6 has a steeper inclination angle and a shorter cell pitch and a higher cell density than the inclination of the reflective inclined portion 4b shown in FIG.

As shown in FIG. 7, a quadrangular pyramid concave mirror can be provided under the translucent dielectric film TF for each cell surrounded by the conductor connecting portion 4a. However, as shown in FIG. The cells of the conductive dielectric film TF may be arranged in all lattices having the same pitch and the same size and intersecting each other at an angle of 60 degrees. Further, as shown in FIG. 9, the shape, size, and height of each of the divided translucent dielectric films TF may be configured randomly. In the case of random arrangement of the cells (translucent dielectric film TF) surrounded by the conductor connection portion 4a, random reflection is obtained, and the light scattering effect is increased.

FIG. 10 is a perspective view showing a modification of each shape of the translucent dielectric film TF surrounded by the conductor connecting portion 4a and the reflective inclined portion 4b. The translucent dielectric film TF may be composed of a polyhedron in addition to a rectangular parallelepiped shape, such as a quadrangular pyramid shape as shown in FIG. 10A, a hexagonal pyramid shape as shown in FIG. It may be oval or conical as shown in (c). In the above description, the case where each shape of the translucent dielectric film TF is a cone is illustrated, but the translucent dielectric film TF has a truncated cone shape or a truncated pyramid shape. Also good. Also. Each vertex of the translucent dielectric film TF may be round and warped.

According to the above modification, the inner surfaces of the plurality of cells surrounded by the conductor connecting portion 4a and the reflective inclined portion 4b exhibit the effect of a concave mirror. Furthermore, by adopting a configuration in which the translucent dielectric film TF is embedded at the interface of the conductive film CF (cathode), the applied voltage as the cathode can be applied in a balanced manner. Moreover, since it functions as a reflection part of the conductor connection part 4a, light can be extracted outside with a relatively short optical path length and a relatively small number of reflections, and the light extraction efficiency can be dramatically improved.

In any of the above-described embodiments, a quartz or glass plate, a metal plate or metal foil, a bent resin substrate, a plastic film, a sheet, or the like is used as the translucent substrate 1. In particular, a glass plate or a transparent plate made of a synthetic resin such as polyester, polymethacrylate, polycarbonate, or polysulfone is preferable. When using a synthetic resin substrate, it is necessary to pay attention to gas barrier properties. If the gas barrier property of the substrate is too small, the organic EL element may be deteriorated by the outside air that has passed through the substrate. Therefore, a method of securing a gas barrier property by providing a dense silicon oxide film or the like on at least one surface of the synthetic resin substrate is also a preferable method.

In any of the above-described embodiments, the organic layer is a light emitting laminate, but the light emitting laminate can also be configured by lamination of inorganic material films.

DESCRIPTION OF SYMBOLS 1 Translucent substrate 2 Translucent electrode layer 3 Organic layer 3a Hole injection layer 3b Hole transport layer 3c Light emitting layer 3d Electron transport layer 3e Electron injection layer 4 Reflective metal film 4a Conductor connection part TF Translucent dielectric film CF conductive film

Claims

An organic electroluminescence device including an organic layer sandwiched between a light-transmitting electrode layer and a reflective metal electrode layer and including a light-emitting layer,
The reflective metal electrode layer includes a translucent conductive film in contact with the organic layer, a translucent dielectric film in contact with the conductive film and having a refractive index equal to or greater than a refractive index of the organic layer, An organic electroluminescence element, comprising: a reflective metal film in contact with the translucent dielectric film, wherein at least a part of the reflective metal film is electrically connected to the conductive film.
The light emitting layer has an optical distance from the conductive film that is ¼ of the light emitting peak wavelength of the light emitting layer, and an optical distance from the reflective metal film that is the light emitting peak of the light emitting layer. 2. The organic electroluminescence device according to claim 1, wherein the organic electroluminescence device has a light emitting surface that is an odd multiple of 3 times or more of a quarter wavelength.
3. The organic electroluminescence device according to claim 2, wherein the reflective metal film is disposed at a position separated from the light emitting surface by a half wavelength or more of a light emission peak wavelength of the light emitting layer.
3. The organic electroluminescence device according to claim 2, wherein the conductive film is a metal thin film having a transmittance of 50% or more in a visible light wavelength band.
3. The organic electroluminescence element according to claim 2, wherein the reflective metal film has a connection portion in contact with the conductive film at an edge portion thereof.
3. The organic electroluminescence element according to claim 2, wherein the reflective metal film has at least one protrusion that penetrates the translucent dielectric film and contacts the conductive film.
The organic electroluminescence device according to claim 6, wherein the reflective metal film has a reflective inclined portion on a side surface of the protruding portion.