JP5063007B2 - Organic electroluminescence device - Google Patents

Description

  The present invention relates to an organic electroluminescent element (hereinafter abbreviated as an organic EL element). In particular, the present invention relates to an organic EL element that emits light with high luminance with low driving force.

  An organic electroluminescent element using a thin film material that emits light when excited by passing an electric current is known. Since organic electroluminescent devices can emit light with high brightness at low voltage, they are widely used in a wide range of fields including mobile phone displays, personal digital assistants (PDAs), computer displays, automobile information displays, TV monitors, or general lighting. It has potential applications and has advantages such as thinning, lightening, miniaturization, and power saving of devices in these fields. For this reason, the expectation as a leading role of the future electronic display market is great. However, in order to be practically used in these fields in place of conventional displays, many technical improvements such as light emission luminance and color tone, durability under a wide range of usage conditions, low cost and large productivity are problems. ing.

  One particular problem is improvement in luminance and driving power. Many of the above-described devices have a problem of achieving high brightness first in reducing the thickness, weight, and size. In reducing the thickness and weight, not only the device but also the drive power source must be made compact and lightweight. In particular, when power is supplied from a primary battery or a secondary battery, power saving is a major issue, and there is a strong demand for high brightness with a low driving voltage. Conventionally, in order to achieve high brightness, a high voltage is required, resulting in faster power consumption. Also, high brightness and high voltage have resulted in a loss of device durability.

Attempts have been made to arrange an organic compound layer doped with a metal dopant as an acceptor in the hole transport layer (see, for example, Patent Documents 1 and 2). However, introducing an acceptor into the hole transport layer is disadvantageous in terms of luminous efficiency. In addition, it has been proposed to continuously change the acceptor concentration of the hole transport layer so that the portion close to the light emitting layer becomes higher (see, for example, Patent Document 3). However, in this case, the effect of the acceptor is not sufficiently exhibited, and a sufficient improvement effect cannot be obtained regardless of the light emission efficiency and the driving durability.
Japanese Patent Laid-Open No. 4-297076 JP 2000-196140 A WO2005-064994A1

  An object of the present invention is to provide an organic EL device having particularly high luminous efficiency and high durability.

The above-described problems of the present invention have been solved by the following means.
<1> An organic electroluminescent element having at least one light emitting layer between an anode electrode and a cathode electrode facing each other, wherein a metal oxide and a metal are included as an acceptor between the light emitting layer and the anode electrode. A hole injection layer containing no organic compound, and having a hole transport layer substantially not containing an acceptor between the hole injection layer and the light emitting layer, the hole injection layer in the hole injection layer The concentration of the metal oxide is lower in the portion closer to the light emitting layer than the portion close to the anode electrode, and the organic compound has a uniform concentration, or the portion on the anode electrode side and the portion on the light emitting layer side. An organic electroluminescent device characterized in that the concentration is lower than the portion between them.
<2> The ratio (Cmax / Cmin) of the concentration (Cmax) of the region having the highest concentration of the metal oxide to the concentration (Cmin) of the lowest concentration in the hole injection layer is 2 or more. The organic electroluminescent element as described in <1> characterized by these.
<3> The organic electroluminescent element according to <1> or <2>, wherein the metal oxide as the acceptor is a metal oxide capable of forming a charge transfer complex.
< 4 > The organic electroluminescent element according to any one of <1> to < 3 >, wherein the metal oxide is molybdenum oxide or vanadium oxide.
< 5 > The organic electroluminescent element according to < 4 >, wherein the organic compound is 7,7,8,8-tetrafluorotetracyanoquinodimethane.

Conventionally, it has been known that an organic layer having an acceptor is provided to control the mobility of holes to improve driving durability, but there is a drawback that the luminous efficiency is lowered, and the high luminous efficiency. And high driving durability are difficult to achieve at the same time.
As a result of diligent efforts, the present inventors have an organic layer containing a metal oxide as an acceptor, and the concentration of the metal oxide in the organic layer is closer to the light emitting layer than the portion closer to the anode electrode. By lowering the concentration, it was possible to maintain high luminous efficiency and realize high driving durability, and reached the present invention. More preferably, the object of the present application is achieved by arranging a layer containing an acceptor as a hole injection layer and disposing a hole transport layer substantially not containing an acceptor between the hole injection layer and the light emitting layer.

  According to the present invention, there is provided an organic EL element capable of obtaining high luminance light emission with a low driving voltage. Furthermore, an organic EL element that is capable of obtaining high-luminance light emission at a low driving voltage and has excellent driving durability is provided.

  Hereinafter, the organic EL device of the present invention will be described in detail.

(Constitution)
The organic electroluminescent element of the present invention has an organic compound layer including at least a light emitting layer between a pair of electrodes (anode and cathode), and more preferably, a hole transport layer is provided between the anode and the light emitting layer. In addition, an electron transport layer is provided between the cathode and the light emitting layer.
From the nature of the light emitting element, it is preferable that at least one of the pair of electrodes is transparent.

  In the present invention, the organic compound layer is preferably laminated in the order of the hole transport layer, the light emitting layer, and the electron transport layer from the anode side. Further, a hole injection layer is provided between the hole transport layer and the anode, and / or an electron transporting intermediate layer is provided between the light emitting layer and the electron transport layer. Further, a hole transporting intermediate layer may be provided between the light emitting layer and the hole transport layer, and similarly, an electron injection layer may be provided between the cathode and the electron transport layer.

  A preferred embodiment of the organic compound layer in the organic electroluminescence device of the present invention is, in order from the anode side, at least (1) a hole injection layer, a hole transport layer (the hole injection layer and the hole transport layer may serve as both). Good), a hole transporting intermediate layer, a light emitting layer, an electron transport layer, and an electron injection layer (the electron transport layer and the electron injection layer may serve both), (2) hole injection layer, hole Transport layer (hole injection layer and hole transport layer may serve as well), light emitting layer, electron transport intermediate layer, electron transport layer, and electron injection layer (electron transport layer and electron injection layer may serve as well) (3) hole injection layer, hole transport layer (hole injection layer and hole transport layer may be combined), hole transport intermediate layer, light emitting layer, electron transport intermediate layer, This is an embodiment having an electron transport layer and an electron injection layer (the electron transport layer and the electron injection layer may serve as each other).

The hole transporting intermediate layer preferably has at least one of a function of accelerating hole injection into the light emitting layer and a function of blocking electrons.
The electron transporting intermediate layer preferably has at least one of a function of promoting electron injection into the light emitting layer and a function of blocking holes.
Furthermore, it is preferable that at least one of the hole transporting intermediate layer and the electron transporting intermediate layer has a function of blocking excitons generated in the light emitting layer.
In order to effectively express the functions of hole injection promotion, electron injection promotion, hole block, electron block, and exciton block, the hole transporting intermediate layer and the electron transporting intermediate layer are formed of a light emitting layer. It is preferable that it adjoins.
Each layer may be divided into a plurality of secondary layers.

  Next, elements constituting the light emitting device of the present invention will be described in detail.

The organic compound layer in the present invention will be described.
The organic electroluminescent element of the present invention has an organic compound layer including at least one light emitting layer. As the organic compound layer other than the light emitting layer, as described above, a hole injection layer, a hole transport layer, and the like. , Hole transporting intermediate layer, light emitting layer, electron transporting intermediate layer, electron transporting layer, electron injection layer and the like.

  Each layer constituting the organic compound layer can be suitably formed by any of dry film forming methods such as vapor deposition and sputtering, transfer methods, printing methods, coating methods, ink jet methods, and spray methods.

(Acceptor)
1) Metal Oxide Acceptor An acceptor is an electron acceptor, and develops conductivity by transferring a charge from an organic compound serving as a base material to the acceptor. By this charge transfer, the acceptor and the organic compound serving as the base material constitute a charge transfer complex.
Preferred materials include molybdenum oxide, vanadium oxide, rhenium oxide, and NiO.
More preferably, molybdenum oxide, vanadium oxide, and rhenium oxide that can be easily deposited are included. Particularly preferred is molybdenum oxide or vanadium oxide.
The metal oxide acceptor in the present invention is contained in an organic layer between the anode and the light emitting layer.
The layer containing the metal oxide acceptor is preferably a hole injection layer. This is because the hole injecting material of the hole injecting layer originally tends to enter holes. That is, there is a property that electrons are easily removed, and the acceptor accepts these electrons to form a charge transfer complex. In the case where a hole injection layer and a hole transport layer are present, as described in JP-A-2000-196140, the addition of an acceptor to the hole transport layer does not reduce the light emission efficiency. desirable.

  The metal oxide acceptor containing layer has a gradient in the layer so that the concentration of the metal oxide acceptor in the film is lower on the side facing the light emitting layer than on the side facing the anode. To do. The concentration gradient may change stepwise or continuously. Preferably, the concentration (Cmax) of the region having the highest concentration is 1% by mass to 100% by mass, more preferably 5% by mass to 50% by mass, and the concentration (Cmin) of the region having the lowest concentration is preferably It is 0.1 mass%-50 mass%, More preferably, it is 1 mass%-10 mass%. The ratio of Cmax to Cmin (Cmax / Cmin) is preferably 2 or more, more preferably 5 or more.

The deposition amount of the acceptor is controlled by the concentration with respect to the hole injecting material or hole transporting material that becomes the base material. As a specific method, the concentration can be controlled by changing the temperature at which the hole injection material or hole transport material is heated and the temperature at which the acceptor material is heated.
When increasing the concentration, the temperature at which the acceptor material is heated can be increased, and the temperature at which the hole injection material or hole transport material is heated can be decreased. When the concentration is lowered, the temperature at which the acceptor material is heated can be lowered, and the temperature at which the hole injection material or the hole transport material is heated can be raised.
Moreover, as shown in WO2005-064994A1, it is also possible to control by changing the distance between the substrate to be deposited and the hole injection material or hole transport material, and the distance between the substrate to be deposited and the acceptor material. is there. In increasing the concentration, the distance between the substrate to be deposited and the hole injection material or the acceptor material is increased, and the distance between the substrate to be deposited and the acceptor material is decreased.
The pattern for changing the density may be changed stepwise or continuously. In the case of stepwise change, after co-depositing the hole injection material or hole transport material and the acceptor material as the base material at a certain concentration, the hole injection material or hole transport is again performed at another concentration. The material and the acceptor material may be co-evaporated. When changing continuously, the temperature at which the hole injection material or hole transport material is heated and the temperature at which the acceptor material is heated are continuously changed, or the substrate to be deposited and the hole injection material or hole transport material are changed. This is possible by changing the distance between the substrate and the acceptor material to be deposited.

2) Second acceptor The second acceptor in the present invention is selected from organic compounds containing no metal. Such an acceptor which does not contain a metal becomes an electron acceptor for an organic compound serving as a base material, and can generate conductivity.
Preferable materials include F4-TCNQ (7,7,8,8-tetrafluorotetracyanoquinodimethane), TCNQ (tetracyanoethylene), TCNE (tetracyanoethylene) and the like containing a cyano group.
Similar to the metal compound acceptor, acceptors are used for the hole injection layer and the hole transport layer. When a hole injection layer and a hole transport layer are present, as described in JP-A No. 2000-196140, it is desirable not to add an acceptor to the hole transport layer in terms of not reducing luminous efficiency. . The density pattern of the second acceptor may be uniform or changed with respect to the first density pattern, but basically it is F4-TCNQ as described in WO2005-064994A1. In order to prevent leakage, the concentration on the electrode side is smaller than the other parts, and in order to prevent the efficiency from being reduced due to the fact that electrons do not contribute to light emission (electron escape), the concentration on the interface side with the hole transport layer is also different from that of other parts. It is better to make it smaller than the part. The pattern for changing the density is the same as that of the first acceptor.

  The concentration of the organic compound containing no metal in the organic layer containing the organic compound containing no metal is preferably 0.01% by mass to 10% by mass, more preferably 0.05% by mass to 1% by mass. is there.

(Hole injection layer, hole transport layer)
The hole injection layer and the hole transport layer are layers having a function of receiving holes from the anode or the anode side and transporting them to the cathode side.

  The hole injection layer preferably contains a dopant which becomes a carrier for hole movement. As a dopant to be introduced into the hole injection layer, an inorganic compound or an organic compound can be used as long as it has an electron accepting property and oxidizes an organic compound. Specifically, the inorganic compound is ferric chloride or aluminum chloride. Lewis acid compounds such as gallium chloride, indium chloride, and antimony pentachloride can be preferably used.

In the case of an organic compound, a compound having a nitro group, a halogen, a cyano group, a trifluoromethyl group, or the like as a substituent, a quinone compound, an acid anhydride compound, or fullerene can be preferably used.
Specifically, hexacyanobutadiene, hexacyanobenzene, tetracyanoethylene, tetracyanoquinodimethane, tetrafluorotetracyanoquinodimethane, p-fluoranyl, p-chloranil, p-bromanyl, p-benzoquinone, 2,6-dichlorobenzoquinone 2,5-dichlorobenzoquinone, tetramethylbenzoquinone, 1,2,4,5-tetracyanobenzene, o-dicyanobenzene, p-dicyanobenzene, 1,4-dicyanotetrafluorobenzene, 2,3-dichloro-5 , 6-dicyanobenzoquinone, p-dinitrobenzene, m-dinitrobenzene, o-dinitrobenzene, p-cyanonitrobenzene, m-cyanonitrobenzene, o-cyanonitrobenzene, 1,4-naphthoquinone, 2,3-dichloronaphthoquinone, 1 Nitronaphthalene, 2-nitronaphthalene, 1,3-dinitronaphthalene, 1,5-dinitronaphthalene, 9-cyanoanthracene, 9-nitroanthracene, 9,10-anthraquinone, 1,3,6,8-tetranitrocarbazole, Examples include 2,4,7-trinitro-9-fluorenone, 2,3,5,6-tetracyanopyridine, maleic anhydride, phthalic anhydride, C60, and C70.

  Among these, hexacyanobutadiene, hexacyanobenzene, tetracyanoethylene, tetracyanoquinodimethane, tetrafluorotetracyanoquinodimethane, p-fluoranyl, p-chloranil, p-bromanyl, p-benzoquinone, 2,6-dichlorobenzoquinone, 2 , 5-dichlorobenzoquinone, 1,2,4,5-tetracyanobenzene, 1,4-dicyanotetrafluorobenzene, 2,3-dichloro-5,6-dicyanobenzoquinone, p-dinitrobenzene, m-dinitrobenzene, o-dinitrobenzene, 1,4-naphthoquinone, 2,3-dichloronaphthoquinone, 1,3-dinitronaphthalene, 1,5-dinitronaphthalene, 9,10-anthraquinone, 1,3,6,8-tetranitrocarbazole, 2,4,7-trinitro-9- Preferred are luolenone, 2,3,5,6-tetracyanopyridine, or C60, hexacyanobutadiene, hexacyanobenzene, tetracyanoethylene, tetracyanoquinodimethane, tetrafluorotetracyanoquinodimethane, p-fluoranyl, p-chloranil. P-bromanyl, 2,6-dichlorobenzoquinone, 2,5-dichlorobenzoquinone, 2,3-dichloronaphthoquinone, 1,2,4,5-tetracyanobenzene, 2,3-dichloro-5,6-dicyanobenzoquinone Or 2,3,5,6-tetracyanopyridine is particularly preferred.

These electron-accepting dopants may be used alone or in combination of two or more.
Although the usage-amount of an electron-accepting dopant changes with kinds of material, it is preferable that it is 0.01 mass%-50 mass% with respect to hole injection layer material, and it is 0.05 mass%-20 mass%. It is further more preferable and it is especially preferable that it is 0.1 mass%-10 mass%. When the amount used is less than 0.01% by mass relative to the hole injecting material, the effect of the present invention is insufficient because it is insufficient, and when it exceeds 50% by mass, the hole injecting ability is impaired. .

  When the hole injection layer contains an acceptor, the hole transport layer preferably contains substantially no acceptor.

  Specific examples of materials for the hole injection layer and the hole transport layer include pyrrole derivatives, carbazole derivatives, pyrazole derivatives, triazole derivatives, oxazole derivatives, oxadiazole derivatives, imidazole derivatives, polyarylalkane derivatives, pyrazoline derivatives, Pyrazolone derivatives, phenylenediamine derivatives, arylamine derivatives, amino-substituted chalcone derivatives, styrylanthracene derivatives, fluorenone derivatives, hydrazone derivatives, stilbene derivatives, silazane derivatives, aromatic tertiary amine compounds, styrylamine compounds, aromatic dimethylidin compounds, A layer containing a porphyrin compound, an organic silane derivative, carbon, or the like is preferable.

The thicknesses of the hole injection layer and the hole transport layer are not particularly limited, but the thickness is preferably 1 nm to 5 μm from the viewpoint of driving voltage reduction, light emission efficiency improvement, durability improvement, The thickness is further preferably 5 nm to 1 μm, and particularly preferably 10 nm to 500 nm.
The hole injection layer and the hole transport layer may have a single-layer structure composed of one or more of the materials described above, or may have a multilayer structure composed of a plurality of layers having the same composition or different compositions. .

When the carrier transport layer adjacent to the light emitting layer is a hole transport layer, the driving durability is such that the Ip (HTL) of the hole transport layer is smaller than the Ip (D) of the dopant contained in the light emitting layer. This is preferable.
Ip (HTL) in the hole transport layer can be measured by a method of measuring Ip described later.

In addition, the carrier mobility in the hole transport layer is generally 10 ⁻⁷ cm ² · V ⁻¹ · s ⁻¹ or more and 10 ⁻¹ cm ² · V ⁻¹ · s ⁻¹ or less. From the viewpoint of efficiency, it is preferably 10 ⁻⁵ cm ² · V ⁻¹ · s ⁻¹ or more and 10 ⁻¹ cm ² · V ⁻¹ · s ⁻¹ or less, preferably 10 ⁻⁴ cm ² · V ⁻¹ · s ⁻¹ or more. ^-1 cm ² · V ^-1 · s ^-1 or less is more preferable, and 10 ^-3 cm ² · V ^-1 · s ^-1 or more and 10 ^-1 cm ² · V ^-1 · s ^-1 or less is particularly preferable.
As the carrier mobility, a value measured by a method similar to the method for measuring the carrier mobility of the light emitting layer is adopted.
The carrier mobility of the hole transport layer is preferably larger than the carrier mobility of the light emitting layer from the viewpoint of driving durability and light emission efficiency.

(Electron injection layer, electron transport layer)
The electron injection layer and the electron transport layer are layers having any one of a function of injecting electrons from the cathode, a function of transporting electrons, and a function of blocking holes that can be injected from the anode.

The electron donating dopant introduced into the electron injecting layer or the electron transporting layer only needs to have an electron donating property and a property of reducing an organic compound, such as an alkali metal such as Li or an alkaline earth metal such as Mg. Transition metals including rare earth metals are preferably used.
In particular, a metal having a work function of 4.2 eV or less can be preferably used. Specifically, Li, Na, K, Be, Mg, Ca, Sr, Ba, Y, Cs, La, Sm, Gd, Yb, and the like Is mentioned.

These electron donating dopants may be used alone or in combination of two or more.
The amount of the electron donating dopant varies depending on the type of material, but is preferably 0.1% by mass to 99% by mass, and 1.0% by mass to 80% by mass with respect to the electron transport layer material. Is more preferable, and 2.0 mass% to 70 mass% is particularly preferable. When the amount used is less than 0.1% by mass with respect to the electron transport layer material, the effect of the present invention is insufficient because it is insufficient, and when it exceeds 99% by mass, the electron transport ability is impaired.

  Specific examples of the material for the electron injection layer and the electron transport layer include pyridine, pyrimidine, triazine, imidazole, triazole, oxazole, oxadiazol, fluorenone, anthraquinodimethane, anthrone, diphenylquinone, thiol. Heterocyclic tetracarboxylic anhydrides such as pyran dioxide, carbodiimide, fluorenylidenemethane, distyrylpyrazine, fluorine-substituted aromatic compounds, naphthaleneperylene, phthalocyanines, and their derivatives (form condensed rings with other rings) Or metal complexes of 8-quinolinol derivatives, metal phthalocyanines, metal complexes having benzoxazole or benzothiazol as ligands, and the like.

The thicknesses of the electron injecting layer and the electron transporting layer are not particularly limited, but the thickness is preferably 1 nm to 5 μm from the viewpoint of lowering driving voltage, improving luminous efficiency, and improving durability. It is more preferably 1 μm, and particularly preferably 10 nm to 500 nm.
The electron injection layer and the electron transport layer may have a single layer structure composed of one or more of the above-described materials, or may have a multilayer structure composed of a plurality of layers having the same composition or different compositions.
When the carrier transport layer adjacent to the light emitting layer is an electron transport layer, the Ea (ETL) of the electron transport layer is greater than the dopant Ea (D) contained in the light emitting layer. Is preferable.

As the Ea (ETL), a value measured by the same method as the Ea measuring method described later is used.
The carrier mobility in the electron transport layer is generally 10 ⁻⁷ cm ² · V ⁻¹ · s ⁻¹ or more and 10 ⁻¹ cm ² · V ⁻¹ · s ⁻¹ or less. From the point of 10 ⁻⁵ cm ² · V ⁻¹ · s ^{−1 to} 10 ⁻¹ cm ² · V ⁻¹ · s ^{−1 and} preferably 10 ⁻⁴ cm ² · V ⁻¹ · s ^{−1 to} 10 ^{− 1 cm 2 · V -1 · s} -1 more preferably less, particularly preferably ^{10 -3 cm 2 · V -1 ·} s -1 or ^{10 -1 cm 2 · V -1 ·} s -1 or less.
The carrier mobility of the electron transport layer is preferably larger than the carrier mobility of the light emitting layer from the viewpoint of driving durability. The carrier mobility was measured in the same manner as the hole transport layer measurement method.
In the carrier mobility of the light-emitting element in the present invention, the carrier mobility in the hole transport layer, electron transport layer, and light-emitting layer is (electron transport layer ≧ hole transport layer)> light-emitting layer. From the viewpoint of sex.
As a host material contained in the buffer layer, a hole transporting host or an electron transporting host described later can be suitably used.

(Light emitting layer)
The light emitting layer receives holes from the anode, hole injection layer, hole transport layer or hole transport buffer layer when an electric field is applied, and receives electrons from the cathode, electron injection layer, electron transport layer or electron transport buffer layer. It is a layer having a function of receiving and providing a field for recombination of holes and electrons to emit light.
The light emitting layer in the present invention contains at least one light emitting dopant and a plurality of host compounds.
Further, the light emitting layer may be a single layer or two or more layers, and each layer may emit light in different emission colors. Even when there are a plurality of light-emitting layers, it is preferable that each layer of the light-emitting layer contains at least one light-emitting dopant and a plurality of host compounds.

As the luminescent dopant and the plurality of host compounds contained in the light emitting layer in the present invention, triplet excitons can be obtained by combining a fluorescent luminescent dopant capable of emitting light (fluorescence) from singlet excitons and a plurality of host compounds. A combination of a phosphorescent dopant capable of obtaining light emission (phosphorescence) from a plurality of host compounds may be used.
The light emitting layer in the present invention can contain two or more kinds of light emitting dopants in order to improve color purity and to broaden the light emission wavelength region.

《Luminescent dopant》
As the luminescent dopant in the present invention, any of phosphorescent luminescent materials and fluorescent luminescent materials can be used as the dopant.
The luminescent dopant in the present invention is a dopant satisfying at least one of the relations of 1.2 eV>ΔIp> 0.2 eV and 1.2 eV>ΔEa> 0.2 eV with the host compound. Is preferable from the viewpoint of driving durability.

《Phosphorescent dopant》
In general, examples of the phosphorescent light-emitting dopant include complexes containing a transition metal atom or a lanthanoid atom.
For example, the transition metal atom is not particularly limited, but preferably includes ruthenium, rhodium, palladium, tungsten, rhenium, osmium, iridium, and platinum, more preferably rhenium, iridium, and platinum. More preferred are iridium and platinum.
Examples of lanthanoid atoms include lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium. Among these lanthanoid atoms, neodymium, europium, and gadolinium are preferable.

Examples of the ligand of the complex include G.I. Wilkinson et al., Comprehensive Coordination Chemistry, Pergamon Press, 1987, H.C. Examples include ligands described in Yersin's "Photochemistry and Photophysics of Coordination Compounds" published by Springer-Verlag 1987, Akio Yamamoto "Organic Metal Chemistry-Fundamentals and Applications-" .
Specific ligands are preferably halogen ligands (preferably chlorine ligands), aromatic carbocyclic ligands (eg, cyclopentadienyl anion, benzene anion, or naphthyl anion), Nitrogen-containing heterocyclic ligand (eg, phenylpyridine, benzoquinoline, quinolinol, bipyridyl, or phenanthroline), diketone ligand (eg, acetylacetone), carboxylic acid ligand (eg, acetic acid ligand) , Alcoholate ligands (eg, phenolate ligands), carbon monoxide ligands, isonitrile ligands, and cyano ligands, more preferably nitrogen-containing heterocyclic ligands.
The complex may have one transition metal atom in the compound, or may be a so-called binuclear complex having two or more. Different metal atoms may be contained at the same time.

  Among these, specific examples of the luminescent dopant include, for example, US6303238B1, US6097147, WO00 / 57676, WO00 / 70655, WO01 / 08230, WO01 / 39234A2, WO01 / 41512A1, WO02 / 02714A2, WO02 / 15645A1, WO02 / 44189A1. JP-A No. 2001-247859, Japanese Patent Application No. 2000-33561, JP-A No. 2002-117978, JP-A No. 2002-225352, JP-A No. 2002-235076, JP-A No. 2001-239281, JP-A No. 2002-170684, EP No. 12111257, 226495, JP2002-234894, JP2001247478, JP2001298470, JP2002-173684, JP2002 Examples include phosphorescent compounds described in patent documents such as No. 203678, JP-A No. 2002-203679, JP-A No. 2004-357991, Japanese Patent Application No. 2005-75340, and Japanese Patent Application No. 2005-75341. Examples of the luminescent dopant to be satisfied include Ir complex, Pt complex, Cu complex, Re complex, W complex, Rh complex, Ru complex, Pd complex, Os complex, Eu complex, Tb complex, Gd complex, Dy complex, and Ce complex. Can be mentioned. Particularly preferred are Ir complexes, Pt complexes, or Re complexes, among which Ir complexes containing at least one coordination mode of metal-carbon bond, metal-nitrogen bond, metal-oxygen bond, or metal-sulfur bond, Pt Complexes or Re complexes are preferred.

《Fluorescent luminescent dopant》
As the fluorescent light-emitting dopant, generally, benzoxazole, benzimidazole, benzothiazole, styrylbenzene, polyphenyl, diphenylbutadiene, tetraphenylbutadiene, naphthalimide, coumarin, pyran, perinone, oxadiazole, aldazine, Pyraridin, cyclopentadiene, bisstyrylanthracene, quinacridone, pyrrolopyridine, thiadiazolopyridine, cyclopentadiene, styrylamine, aromatic dimethylidin compounds, condensed polycyclic aromatic compounds (anthracene, phenanthroline, pyrene, perylene, rubrene, or pentacene, etc. ), 8-quinolinol metal complexes, various metal complexes represented by pyromethene complexes and rare earth complexes, polythiophene, polyphenylene, polyphenylene Polymeric compounds such as vinylene, organic silane, and the like, and their derivatives.

  Among these, specific examples of the luminescent dopant include the following, but are not limited thereto.

  Among the above, the luminescent dopant used in the present invention is D-2, D-3, D-4, D-5, D-6, D-7, D-8, from the viewpoint of luminous efficiency and durability. D-9, D-10, D-11, D-12, D-13, D-14, D-15, D-16, D-21, D-22, D-23, D-24, or D -25 to D-28 are preferred, D-2, D-3, D-4, D-5, D-6, D-7, D-8, D-12, D-14, D-15, D -16, D-21, D-22, D-23, D-24, or D-25 to D-28 are more preferred, and D-21, D-22, D-23, D-24, or D- More preferred is 25 to D-28.

  The light emitting dopant in the light emitting layer is contained in an amount of 0.1 to 30% by mass with respect to the total mass of the compound generally forming the light emitting layer in the light emitting layer, but from the viewpoint of durability and luminous efficiency. The content is preferably 1% by mass to 15% by mass, and more preferably 2% by mass to 12% by mass.

  The thickness of the light emitting layer is not particularly limited, but is usually preferably 1 nm to 500 nm, and more preferably 5 nm to 200 nm from the viewpoint of light emission efficiency. Is more preferable.

(Host material)
As the host material used in the present invention, a hole transporting host material excellent in hole transportability (sometimes referred to as a hole transportable host) and an electron transporting host compound excellent in electron transportability (electron transportability) May be described as a host).

《Hole-transporting host》
The hole transporting host used in the organic layer of the present invention preferably has an ionization potential Ip of 5.1 eV or more and 6.3 eV or less from the viewpoint of improving durability and lowering driving voltage. It is more preferably 0.1 eV or less, and further preferably 5.6 eV or more and 5.8 eV or less. Further, from the viewpoint of improving durability and lowering driving voltage, the electron affinity Ea is preferably 1.2 eV or more and 3.1 eV or less, more preferably 1.4 eV or more and 3.0 eV or less, and 1.8 eV or more. More preferably, it is 2.8 eV or less.

Specific examples of such a hole transporting host include the following materials.
Pyrrole, carbazole, triazole, oxazole, oxadiazole, pyrazole, imidazole, polyarylalkane, pyrazoline, pyrazolone, phenylenediamine, arylamine, amino-substituted chalcone, styrylanthracene, fluorenone, hydrazone, stilbene, silazane, aromatic tertiary Amine compounds, styrylamine compounds, aromatic dimethylidin compounds, porphyrin compounds, polysilane compounds, poly (N-vinylcarbazole), aniline copolymers, thiophene oligomer thiophene oligomers, conductive polymer oligomers such as polythiophene, organic Examples thereof include silane, carbon film, and derivatives thereof.
Of these, carbazole derivatives, aromatic tertiary amine compounds, and thiophene derivatives are preferable, and those having at least one of a carbazole skeleton and an aromatic tertiary amine skeleton in the molecule are particularly preferable.
Specific examples of such a hole transporting host include, but are not limited to, the following compounds.

《Electron transporting host》
The electron transporting host in the light emitting layer used in the present invention preferably has an electron affinity Ea of 2.5 eV or more and 3.5 eV or less from the viewpoint of improving durability and lowering driving voltage. More preferably, it is 0.2 eV or less, and it is still more preferable that it is 2.8 eV or more and 3.1 eV or less. Further, from the viewpoint of improving durability and reducing driving voltage, the ionization potential Ip is preferably 5.7 eV or more and 7.5 eV or less, more preferably 5.8 eV or more and 7.0 eV or less, and 5.9 eV or more. More preferably, it is 6.5 eV or less.

Specific examples of such an electron transporting host include the following materials.
Pyridine, pyrimidine, triazine, imidazole, pyrazole, triazole, oxazole, oxadiazol, fluorenone, anthraquinodimethane, anthrone, diphenylquinone, thiopyran dioxide, carbodiimide, fluorenylidenemethane, distyrylpyrazine, Fluorine-substituted aromatic compounds, heterocyclic tetracarboxylic anhydrides such as naphthaleneperylene, phthalocyanines, and derivatives thereof (may form condensed rings with other rings), metal complexes and metals of 8-quinolinol derivatives Examples thereof include various metal complexes represented by metal complexes having phthalocyanine, benzoxazole or benzothiazol as a ligand.

Preferred examples of the electron transporting host include metal complexes, azole derivatives (benzimidazole derivatives, imidazopyridine derivatives, etc.), and azine derivatives (pyridine derivatives, pyrimidine derivatives, triazine derivatives, etc.). To metal complex compounds are preferred. The metal complex compound (A) is more preferably a metal complex having a ligand having at least one nitrogen atom, oxygen atom or sulfur atom coordinated to the metal.
The metal ion in the metal complex is not particularly limited, but is preferably beryllium ion, magnesium ion, aluminum ion, gallium ion, zinc ion, indium ion, tin ion, platinum ion, or palladium ion, more preferably beryllium ion, Aluminum ion, gallium ion, zinc ion, platinum ion, or palladium ion, and more preferably aluminum ion, zinc ion, or palladium ion.

  There are various known ligands contained in the metal complex. For example, “Photochemistry and Photophysics of Coordination Compounds”, Springer-Verlag, H.C. Examples include the ligands described in Yersin, published in 1987, “Organometallic Chemistry: Fundamentals and Applications”, Sakai Hanafusa, Yamamoto Akio, published in 1982, and the like.

The ligand is preferably a nitrogen-containing heterocyclic ligand (preferably having 1 to 30 carbon atoms, more preferably 2 to 20 carbon atoms, particularly preferably 3 to 15 carbon atoms, and a monodentate ligand. Alternatively, it may be a bidentate or higher ligand, preferably a bidentate or higher and a hexadentate or lower ligand, or a bidentate or higher and lower 6 or lower ligand and a monodentate mixed ligand. preferable.
Examples of the ligand include an azine ligand (for example, pyridine ligand, bipyridyl ligand, terpyridine ligand, etc.), a hydroxyphenylazole ligand (for example, hydroxyphenylbenzimidazole coordination). And a hydroxyphenyl benzoxazole ligand, a hydroxyphenyl imidazole ligand, a hydroxyphenylimidazopyridine ligand, etc.), an alkoxy ligand (preferably having 1 to 30 carbon atoms, more preferably 1 carbon atom). To 20, particularly preferably 1 to 10 carbon atoms, such as methoxy, ethoxy, butoxy, 2-ethylhexyloxy), aryloxy ligands (preferably 6 to 30 carbon atoms, more preferably 6-20 carbon atoms, particularly preferably 6-12 carbon atoms, for example phenyl Carboxymethyl, 1-naphthyloxy, 2-naphthyloxy, 2,4,6-trimethylphenyl oxy, and 4-biphenyloxy and the like.),

Heteroaryloxy ligand (preferably having 1 to 30 carbon atoms, more preferably 1 to 20 carbon atoms, particularly preferably 1 to 12 carbon atoms, and examples thereof include pyridyloxy, pyrazyloxy, pyrimidyloxy, and quinolyloxy. ), An alkylthio ligand (preferably having 1 to 30 carbon atoms, more preferably 1 to 20 carbon atoms, particularly preferably 1 to 12 carbon atoms, such as methylthio and ethylthio), arylthio ligands (Preferably 6 to 30 carbon atoms, more preferably 6 to 20 carbon atoms, particularly preferably 6 to 12 carbon atoms, such as phenylthio), heteroarylthio ligand (preferably 1 carbon atom) To 30, more preferably 1 to 20 carbon atoms, particularly preferably 1 to 12 carbon atoms, such as pyridylthio , 2-benzimidazolylthio, 2-benzoxazolylthio, 2-benzthiazolylthio, etc.), a siloxy ligand (preferably having 1 to 30 carbon atoms, more preferably 3 to 25 carbon atoms). Particularly preferably, it has 6 to 20 carbon atoms, and examples thereof include a triphenylsiloxy group, a triethoxysiloxy group, and a triisopropylsiloxy group.), An aromatic hydrocarbon anion ligand (preferably having 6 carbon atoms) To 30, more preferably 6 to 25 carbon atoms, particularly preferably 6 to 20 carbon atoms, such as a phenyl anion, a naphthyl anion, an anthranyl anion, etc.), an aromatic heterocyclic anion ligand (preferably Has 1 to 30 carbon atoms, more preferably 2 to 25 carbon atoms, and particularly preferably 2 to 20 carbon atoms. Pyrrole anion, pyrazole anion, pyrazole anion, triazole anion, oxazole anion, benzoxazole anion, thiazole anion, benzothiazole anion, thiophene anion, benzothiophene anion, etc.), indolenine anion ligand, etc. , Preferably a nitrogen-containing heterocyclic ligand, aryloxy ligand, heteroaryloxy group, or siloxy ligand, more preferably a nitrogen-containing heterocyclic ligand, aryloxy ligand, siloxy coordination Or an aromatic hydrocarbon anion ligand or an aromatic heterocyclic anion ligand.

  Examples of the metal complex electron transporting host are described in, for example, JP-A No. 2002-235076, JP-A No. 2004-214179, JP-A No. 2004-221106, JP-A No. 2004-221665, JP-A No. 2004-221068, JP-A No. 2004-327313, etc. The compound of this is mentioned.

  Specific examples of such an electron transporting host include, but are not limited to, the following materials.

  As the electron transport layer host, E-1 to E-6, E-8, E-9, E-21, or E-22 are preferable, and E-3, E-4, E-6, E-8, E-9, E-10, E-21, or E-22 is more preferable, and E-3, E-4, E-21, or E-22 is still more preferable.

  In the light-emitting layer of the present invention, when a phosphorescent dopant is used as the luminescent dopant, the lowest triplet excitation energy T1 (D) of the phosphorescent dopant and the lowest excited triplet energy of the plurality of host compounds It is preferable in terms of color purity, light emission efficiency, and driving durability that the above T1 (H) min satisfies the relationship of T1 (H) min> T1 (D).

  Further, the content of the host compound in the present invention is not particularly limited, but from the viewpoint of luminous efficiency and driving voltage, it is 15% by mass to 85% by mass with respect to the total compound mass forming the light emitting layer. Preferably there is.

The carrier mobility in the light emitting layer is generally 10 ⁻⁷ cm ² · V ⁻¹ · s ⁻¹ or more and 10 ⁻¹ cm ² · V ⁻¹ · s ⁻¹ or less. From the point, it is preferably 10 ⁻⁶ cm ² · V ⁻¹ · s ⁻¹ or more and 10 ⁻¹ cm ² · V ⁻¹ · s ⁻¹ or less, preferably 10 ⁻⁵ cm ² · V ⁻¹ · s ⁻¹ or more and 10 ^−1. cm ² · V ^-1 · s ^-1 more preferably less, particularly preferably ^{10 -4 cm 2 · V -1 ·} s -1 or ^{10 -1 cm 2 · V -1 ·} s -1 or less.

The carrier mobility of the light emitting layer is preferably smaller than the carrier mobility of the carrier transport layer described later, from the viewpoints of light emission efficiency and driving durability.
The carrier mobility was measured by the Time of Flight method, and the obtained value was defined as the carrier mobility.

(Hole blocking layer)
The hole blocking layer is a layer having a function of preventing holes transported from the anode side to the light emitting layer from passing through to the cathode side. In the present invention, a hole blocking layer can be provided as an organic compound layer adjacent to the light emitting layer on the cathode side.
Although a hole block layer is not specifically limited, Specifically, aluminum complexes, such as BAlq, a triazole derivative, a pyraza ball derivative, etc. can be contained.
In addition, the thickness of the hole blocking layer is generally preferably 50 nm or less, preferably 1 nm to 50 nm, and more preferably 5 nm to 40 nm in order to lower the driving voltage.

(anode)
The anode usually has a function as an electrode for supplying holes to the organic compound layer, and there is no particular limitation on the shape, structure, size, etc., depending on the use and purpose of the light-emitting element. , Can be appropriately selected from known electrode materials. As described above, the anode is usually provided as a transparent anode.

  As a material of the anode, for example, a metal, an alloy, a metal oxide, a conductive compound, or a mixture thereof can be suitably cited, and a material having a work function of 4.0 eV or more is preferable. Specific examples of the anode material include conductive metals such as tin oxide doped with antimony and fluorine (ATO, FTO), tin oxide, zinc oxide, indium oxide, indium tin oxide (ITO), and indium zinc oxide (IZO). Metals such as oxides, gold, silver, chromium, nickel, and mixtures or laminates of these metals and conductive metal oxides, inorganic conductive materials such as copper iodide and copper sulfide, polyaniline, polythiophene, polypyrrole, etc. Organic conductive materials, and a laminate of these and ITO. Among these, conductive metal oxides are preferable, and ITO is particularly preferable from the viewpoints of productivity, high conductivity, transparency, and the like.

  The anode is composed of, for example, a wet method such as a printing method and a coating method, a physical method such as a vacuum deposition method, a sputtering method, and an ion plating method, and a chemical method such as a CVD and a plasma CVD method. It can be formed on the substrate according to a method appropriately selected in consideration of suitability with the material to be processed. For example, when ITO is selected as the anode material, the anode can be formed according to a direct current or high frequency sputtering method, a vacuum deposition method, an ion plating method, or the like.

  In the organic electroluminescent element of the present invention, the formation position of the anode is not particularly limited and can be appropriately selected according to the use and purpose of the light emitting element. The anode may be formed on the entire one surface of the substrate, or may be formed on a part thereof.

  The patterning for forming the anode may be performed by chemical etching such as photolithography, or may be performed by physical etching such as laser, or vacuum deposition or sputtering with a mask overlapped. It may be performed by a lift-off method or a printing method.

  The thickness of the anode can be appropriately selected depending on the material constituting the anode and cannot be generally defined, but is usually about 10 nm to 50 μm, and preferably 50 nm to 20 μm.

The resistance value of the anode is preferably 10 ³ Ω / □ or less, and more preferably 10 ² Ω / □ or less. When the anode is transparent, it may be colorless and transparent or colored and transparent. In order to take out light emission from the transparent anode side, the transmittance is preferably 60% or more, and more preferably 70% or more.

  The transparent anode is described in detail in the book “New Development of Transparent Electrode Films” published by CMC (1999), supervised by Yutaka Sawada, and the matters described here can be applied to the present invention. In the case of using a plastic substrate having low heat resistance, a transparent anode formed using ITO or IZO at a low temperature of 150 ° C. or lower is preferable.

(cathode)
The cathode usually has a function as an electrode for injecting electrons into the organic compound layer, and there is no particular limitation on the shape, structure, size, etc., depending on the use and purpose of the light-emitting element, It can select suitably from well-known electrode materials.

  Examples of the material constituting the cathode include metals, alloys, metal oxides, electrically conductive compounds, and mixtures thereof, and those having a work function of 4.5 eV or less are preferable. Specific examples include alkali metals (for example, Li, Na, K, or Cs), alkaline earth metals (for example, Mg, Ca, etc.), gold, silver, lead, aluminum, sodium-potassium alloys, lithium-aluminum alloys, And a rare earth metal such as magnesium-silver alloy, indium, and ytterbium. These may be used alone, but two or more can be suitably used in combination from the viewpoint of achieving both stability and electron injection.

Among these, as a material constituting the cathode, an alkali metal or an alkaline earth metal is preferable from the viewpoint of electron injecting property, and a material mainly composed of aluminum is preferable from the viewpoint of excellent storage stability.
The material mainly composed of aluminum is aluminum alone, an alloy of aluminum and 0.01% by mass to 10% by mass of alkali metal or alkaline earth metal, or a mixture thereof (for example, lithium-aluminum alloy, magnesium-aluminum alloy). Etc.).

  The materials for the cathode are described in detail in JP-A-2-15595 and JP-A-5-121172, and the materials described in these public relations can also be applied in the present invention.

There is no restriction | limiting in particular about the formation method of a cathode, According to a well-known method, it can carry out.
For example, the cathode described above is configured from a wet method such as a printing method or a coating method, a physical method such as a vacuum deposition method, a sputtering method, or an ion plating method, or a chemical method such as CVD or plasma CVD method. It can be formed according to a method appropriately selected in consideration of suitability with the material. For example, when a metal or the like is selected as the cathode material, one or more of them can be simultaneously or sequentially performed according to a sputtering method or the like.

  Patterning when forming the cathode may be performed by chemical etching such as photolithography, physical etching by laser, or the like, or by vacuum deposition or sputtering with the mask overlaid. It may be performed by a lift-off method or a printing method.

In the present invention, the cathode formation position is not particularly limited, and may be formed on the entire organic compound layer or a part thereof.
Further, a dielectric layer made of an alkali metal or alkaline earth metal fluoride or oxide may be inserted between the cathode and the organic compound layer with a thickness of 0.1 nm to 5 nm. This dielectric layer can also be regarded as a kind of electron injection layer. The dielectric layer can be formed by, for example, a vacuum deposition method, a sputtering method, an ion plating method, or the like.

The thickness of the cathode can be appropriately selected depending on the material constituting the cathode and cannot be generally defined, but is usually about 10 nm to 5 μm, and preferably 50 nm to 1 μm.
Further, the cathode may be transparent or opaque. The transparent cathode can be formed by depositing a thin cathode material to a thickness of 1 nm to 10 nm and further laminating a transparent conductive material such as ITO or IZO.

(substrate)
In the present invention, a substrate can be used. The substrate used is preferably a substrate that does not scatter or attenuate light emitted from the organic compound layer. Specific examples include zirconia-stabilized yttrium (YSZ), inorganic materials such as glass, polyesters such as polyethylene terephthalate, polybutylene phthalate, and polyethylene naphthalate, polystyrene, polycarbonate, polyethersulfone, polyarylate, polyimide, and polycycloolefin. , Norbornene resins, and organic materials such as poly (chlorotrifluoroethylene).
For example, when glass is used as the substrate, alkali-free glass is preferably used as the material in order to reduce ions eluted from the glass. Moreover, when using soda-lime glass, it is preferable to use what gave barrier coatings, such as a silica. In the case of an organic material, it is preferable that it is excellent in heat resistance, dimensional stability, solvent resistance, electrical insulation, and workability.

  There is no restriction | limiting in particular about the shape of a board | substrate, a structure, a magnitude | size, It can select suitably according to the use, purpose, etc. of a light emitting element. In general, the shape of the substrate is preferably a plate shape. The structure of the substrate may be a single layer structure, a laminated structure, may be formed of a single member, or may be formed of two or more members.

  The substrate may be colorless and transparent or colored and transparent, but is preferably colorless and transparent in that it does not scatter or attenuate light emitted from the organic light emitting layer.

The substrate can be provided with a moisture permeation preventing layer (gas barrier layer) on the front surface or the back surface.
As a material for the moisture permeation preventive layer (gas barrier layer), inorganic materials such as silicon nitride and silicon oxide are preferably used. The moisture permeation preventing layer (gas barrier layer) can be formed by, for example, a high frequency sputtering method.
When a thermoplastic substrate is used, a hard coat layer, an undercoat layer, or the like may be further provided as necessary.

(Protective layer)
In the present invention, the entire organic EL element may be protected by a protective layer.
As a material contained in the protective layer, any material may be used as long as it has a function of preventing materials that promote device deterioration such as moisture and oxygen from entering the device.
Specific examples thereof include metals such as In, Sn, Pb, Au, Cu, Ag, Al, Ti, and Ni, MgO, SiO, SiO ₂ , Al ₂ O ₃ , GeO, NiO, CaO, BaO, and Fe _2. Metal oxides such as O ₃ , Y ₂ O ₃ , or TiO ₂ , metal nitrides such as SiN _x , SiN _x O _y , metal fluorides such as MgF ₂ , LiF, AlF ₃ , or CaF ₂ , polyethylene, polypropylene Polymethyl methacrylate, polyimide, polyurea, polytetrafluoroethylene, polychlorotrifluoroethylene, polydichlorodifluoroethylene, a copolymer of chlorotrifluoroethylene and dichlorodifluoroethylene, tetrafluoroethylene and at least one comonomer. Copolymer obtained by copolymerizing the monomer mixture containing, cyclic in the copolymer main chain Fluorine-containing copolymer having a structure; 1% by weight of the water absorbing water absorption material, water absorption of 0.1% or less of moisture-proof material, and the like.

  The method for forming the protective layer is not particularly limited, and for example, vacuum deposition, sputtering, reactive sputtering, MBE (molecular beam epitaxy), cluster ion beam, ion plating, plasma polymerization (high frequency) Excited ion plating method), plasma CVD method, laser CVD method, thermal CVD method, gas source CVD method, coating method, printing method, or transfer method can be applied.

(Sealing)
Furthermore, the organic electroluminescent element of this invention may seal the whole element using a sealing container.
Further, a moisture absorbent or an inert liquid may be sealed in a space between the sealing container and the light emitting element. Although it does not specifically limit as a moisture absorber, For example, barium oxide, sodium oxide, potassium oxide, calcium oxide, sodium sulfate, calcium sulfate, magnesium sulfate, phosphorus pentoxide, calcium chloride, magnesium chloride, copper chloride Cesium fluoride, niobium fluoride, calcium bromide, vanadium bromide, molecular sieve, zeolite, magnesium oxide, and the like. The inert liquid is not particularly limited, and examples thereof include fluorinated solvents such as paraffins, liquid paraffins, perfluoroalkanes, perfluoroamines, perfluoroethers, chlorinated solvents, and silicone oils. It is done.

The organic electroluminescence device of the present invention emits light by applying a direct current (which may include an alternating current component as necessary) voltage (usually 2 to 15 volts) or a direct current between the anode and the cathode. Obtainable.
The driving durability of the organic electroluminescent element in the present invention can be measured by the time required to decrease to a certain luminance at a specific luminance. For example, using a source measure unit 2400 made by KEITHLEY, a direct voltage is applied to the organic EL element to emit light, and a continuous driving test is performed under the condition of an initial luminance of 500 cd / m ² , and the luminance becomes 200 cd / m ² The brightness reduction time can be obtained by comparing the brightness reduction time with a conventional light emitting element. This numerical value was used in the present invention.
An important characteristic value of this organic electroluminescence device is external quantum efficiency. The external quantum efficiency is calculated by “external quantum efficiency φ = number of photons emitted from the device / number of electrons injected into the device”, and it can be said that the larger this value, the more advantageous the device in terms of power consumption.

  The external quantum efficiency of the organic electroluminescent element is determined by “external quantum efficiency φ = internal quantum efficiency × light extraction efficiency”. In an organic EL device using fluorescence emission from an organic compound, the limit value of the internal quantum efficiency is 25%, and the light extraction efficiency is approximately 20%. Therefore, the limit value of the external quantum efficiency is approximately 5%. Has been.

It figures external quantum efficiency, the maximum value of the external quantum efficiency when the device is driven at 20 ° C., or around 100cd / m ² ~300cd / m ² when the device is driven at 20 ° C. (preferably 200 cd / The value of the external quantum efficiency at m ² ) can be used.
In the present invention, using a source measure unit type 2400 manufactured by Toyo Technica, a DC constant voltage is applied to the EL element to emit light, and the luminance is measured using a luminance meter BM-8 manufactured by Topcon Corporation, and is 200 cd / m ^2. A value obtained by calculating the external quantum efficiency at is used.

  Further, the external quantum efficiency of the light emitting element can be calculated from the result and the relative luminous efficiency curve obtained by measuring the light emission luminance, the light emission spectrum, and the current density. That is, the number of input electrons can be calculated using the current density value. The emission luminance can be converted into the number of photons emitted by integral calculation using the emission spectrum and the relative visibility curve (spectrum). From these, the external quantum efficiency (%) can be calculated by “(number of emitted photons / number of electrons input to the device) × 100”.

  The driving method of the organic electroluminescence device of the present invention is described in JP-A-2-148687, JP-A-6-301355, JP-A-5-29080, JP-A-7-134558, JP-A-8-234658, and JP-A-8-2441047. The driving methods described in each publication, Japanese Patent No. 2784615, US Pat. Nos. 5,828,429, 6023308, and the like can be applied.

(Use of the organic electroluminescence device of the present invention)
The organic electroluminescent element of the present invention can be suitably used for a display element, a display, a backlight, electrophotography, an illumination light source, a recording light source, an exposure light source, a reading light source, a sign, a signboard, an interior, or optical communication.

  Examples of the organic electroluminescence device of the present invention will be described below, but the present invention is not limited to these examples.

Example 1
1. Production of organic EL element (production of comparative organic EL element A1)
A 0.5 mm thick, 2.5 cm square ITO glass substrate (manufactured by Geomat Co., Ltd., surface resistance 10 Ω / □) is placed in a cleaning container, subjected to ultrasonic cleaning in 2-propanol, and then subjected to UV-ozone treatment for 30 minutes. went. The following layers were deposited on this transparent anode by vacuum deposition. The vapor deposition rate in the examples of the present invention is 0.2 nm / second unless otherwise specified. The deposition rate was measured using a quartz resonator. The film thicknesses described below were also measured using a crystal resonator.

-Hole injection layer (no acceptor)-
Deposition was performed at a deposition rate of 2-TNATA of 0.5 nm / second. The film thickness was 140 nm.
-Hole transport layer-
Vapor deposition was performed on the hole injection layer at a deposition rate of α-NPD of 0.5 nm / second. The film thickness was 10 nm.
-Light emitting layer-
Co-deposition was performed so that CBP as a host was deposited at a deposition rate of 0.1 nm / second and the luminescent dopant tbppy was 12% by mass of the entire organic material in the luminescent layer. The thickness of the light emitting layer was 30 nm.
-Electron transport layer-
ALQ: film thickness 20 nm (deposition rate: 0.1 nm / second)

-Electron injection layer and cathode-
A patterned mask (a mask having a light emitting area of 2 mm × 2 mm) was placed thereon, and lithium fluoride was deposited to 0.5 nm at a deposition rate of 0.1 nm / second to form an electron injection layer. Further, metal aluminum was deposited to a thickness of 100 nm to form a cathode.

The produced laminate was put in a glove box substituted with argon gas, and sealed with a stainless steel sealing can and an ultraviolet curable adhesive (XNR5516HV, manufactured by Nagase Ciba Co., Ltd.).
Thus, a comparative organic EL element A1 was obtained.

(Production of comparative organic EL elements A2 to A4)
In production of the organic EL element A1, comparative organic EL elements A2 to A4 in which an acceptor was added to the hole injection layer as described below were produced.
A2: Metal oxide acceptor contained in uniform concentration distribution (10% by mass) The metal oxide acceptor MoO ₃ was co-deposited at 0.01 nm / s with respect to the hole injection material 2-TNATA 0.09 nm / s.
A3: Metal oxide acceptor contained in uniform concentration distribution (1% by mass) The metal oxide acceptor MoO ₃ was co-deposited at 0.001 nm / s with respect to the hole injection material 2-TNATA 0.099 nm / s.

A4: The hole injection layer is made into two layers, and the metal oxide acceptor is contained in a stepwise concentration (configuration of WO2005-64994A1)
The hole injection layer on the light emitting layer side is a comparative sample containing a metal oxide acceptor at a high concentration.
First, using a metal oxide acceptor MoO ₃ , the hole injection material 2-TNATA was 0.099 nm / s, and MoO ₃ was doped by 0.001 nm / s to 20 nm for vapor deposition.
Further, the hole injection material 2-TNATA was 0.099 nm / s, and MoO ₃ was doped by 260 nm at 0.001 nm / s for vapor deposition.
The MoO ₃ content of the positive hole injection layer on the anode side is 1% by mass, and the MoO ₃ content of the positive hole injection layer on the light emitting layer side is 10% by mass.

(Preparation of organic EL elements 1 to 5)
In the preparation of the organic EL elements A1, was produced organic EL device 1-5 plus acceptor as described in Table 1 in the hole injection layer.
Sample 1: The hole injection layer is made into two layers, and the metal oxide acceptor is contained in a stepwise concentration distribution and low on the light emitting layer side. The metal oxide acceptor MoO with respect to the hole injection material 2-TNATA 0.09 nm / s Vapor deposition was performed by doping ₃ with 20 nm at 0.01 nm / s. Further, the metal oxide acceptor MoO ₃ was doped by 260 nm at 0.001 nm / s with respect to the hole injection material 2-TNATA 0.099 nm / s, and vapor deposition was performed.
The MoO ₃ content of the positive hole injection layer on the anode side is 10% by mass, and the MoO ₃ content of the positive hole injection layer on the light emitting layer side is 1% by mass.

Sample 2: The hole injection layer is made into two layers, and the metal oxide acceptor is contained in a stepwise concentration distribution at a lower level on the light emitting layer side. For the hole injection material 2-TNATA 0.05 nm / s, the metal oxide acceptor MoO Vapor deposition was performed by doping ₃ with 20 nm at 0.05 nm / s. Further, the metal oxide acceptor MoO ₃ was doped by 260 nm at a rate of 0.007 nm / s with respect to the hole injection material 2-TNATA 0.093 nm / s, and vapor deposition was performed.
The MoO ₃ content of the positive hole injection layer on the anode side is 50% by mass, and the MoO ₃ content of the positive hole injection layer on the light emitting layer side is 7% by mass.

Sample 3: The hole injection layer is made into two layers, and a metal oxide acceptor and an organic acceptor are contained in a stepwise concentration distribution at a low level on the light-emitting layer side. Metal oxidation with respect to the hole injection material 2-TNATA 0.899 nm / s The material acceptor MoO ₃ was doped with 20 nm by 0.1 nm / s and the organic acceptor F4-TCNQ 0.001 nm / s, and ternary vapor deposition was performed. Further, ternary vapor deposition was performed by doping metal oxide acceptor MoO ₃ with 0.01 nm / s and organic acceptor F4-TCNQ 0.001 nm / s to 260 nm with respect to hole injection material 2-TNATA 0.989 nm / s. .
The MoO ₃ content of the positive hole injection layer on the anode side is 10% by mass, and the MoO ₃ content of the positive hole injection layer on the light emitting layer side is 1% by mass.

Sample 4: Three hole injection layers are formed, and metal oxide acceptors and organic acceptors are contained in a stepwise concentration distribution at a low level on the light emitting layer side. Metal oxidation with respect to hole injection material 2-TNATA 0.9 nm / s The material acceptor MoO ₃ was doped at a rate of 0.1 nm / s for 20 nm for vapor deposition. Further, ternary deposition was performed by doping metal oxide acceptor MoO ₃ with 0.01 nm / s and organic acceptor F4-TCNQ 0.001 nm / s to 130 nm with respect to hole injection material 2-TNATA 0.989 nm / s. . On top of that, a metal oxide acceptor MoO ₃ was doped at a thickness of 130 nm at 0.01 nm / s to the hole injection material 2-TNATA 0.989 nm / s, and co-evaporation was performed.
MoO ₃ content of the anode side of the hole injection layer is 10 mass%, with MoO ₃ content of the intermediate layer side of the hole injection layer is 1 mass%, MoO ₃ content of the light-emitting layer side of the hole injection layer Is 1% by mass.

Sample 5: The hole injection layer is made into three layers, and a metal oxide acceptor and an organic acceptor are contained in a stepwise concentration distribution at a low level on the light emitting layer side, and an organic acceptor is contained at a high level on the light emitting layer side. Co-deposition was performed by doping metal oxide acceptor MoO ₃ at 0.1 nm / s for 20 nm with respect to TNATA 0.9 nm / s. Further, ternary deposition was performed by doping metal oxide acceptor MoO ₃ with 0.01 nm / s and organic acceptor F4-TCNQ 0.001 nm / s to 130 nm with respect to hole injection material 2-TNATA 0.989 nm / s. . On top of that, the hole injection material 2-TNATA 0.999 nm / s was doped with 130 nm of organic acceptor F4-TCNQ 0.001 nm / s to perform co-evaporation.
MoO ₃ content of the anode side of the hole injection layer is 10 mass%, with MoO ₃ content of the intermediate layer side of the hole injection layer is 1 mass%, MoO ₃ content of the light-emitting layer side of the hole injection layer Is 0% by mass.

  The structure of the compound used for the light-emitting element is shown below.

3. Performance evaluation (evaluation items)
(1) Luminous efficiency The external quantum efficiency of the light-emitting element was calculated from the results and relative luminous efficiency curve obtained by measuring the light emission luminance, light emission spectrum, and current density. The external quantum efficiency (%) was calculated by “(number of photons emitted / number of electrons input to the device) × 100”.
(2) Driving voltage The driving voltage at a driving current density of 10 mA / cm ² was measured.
(3) Driving durability A continuous driving test was performed under the condition of initial luminance of 500 cd / m ² , and the time when the luminance became 200 cd / m ² was determined as the luminance reduction time.

(Evaluation results)
The obtained results are shown in Table 2.
The device of the present invention had a lower driving voltage than the comparative devices A1 and A3, and in particular, the driving durability could be extended. In addition, the light emitting efficiency of the device of the present invention was particularly improved as compared with the comparative devices A2 and A4.

Example 2
1. Preparation of Sample An organic EL element 21 of the present invention was prepared in the same manner as the organic EL element 2 except that an acceptor was added to the hole transport layer for the element 1 of the present invention of Example 1.

2. Performance Evaluation The results evaluated in the same manner as in Example 1 are shown in Table 3.
As a result, the efficiency was reduced by placing the acceptor in the hole transport layer. It was shown that the hole transport layer preferably contained no acceptor.

Claims (5)

An organic electroluminescent element having at least one light emitting layer between an anode and a cathode facing each other, wherein the organic compound does not contain a metal oxide and a metal as an acceptor between the light emitting layer and the anode And a hole transport layer substantially free of an acceptor between the hole injection layer and the light emitting layer, and the metal oxide in the hole injection layer The concentration is lower in the portion closer to the light emitting layer than the portion closer to the anode electrode, and the concentration of the organic compound is uniform or between the portion on the anode electrode side and the portion on the light emitting layer side. An organic electroluminescent element characterized in that the concentration is lower than that of the portion.   The ratio (Cmax / Cmin) of the concentration (Cmax) of the region having the highest concentration of the metal oxide in the hole injection layer to the concentration (Cmin) of the region having the lowest concentration is 2 or more. The organic electroluminescent element according to claim 1.   The organic electroluminescence device according to claim 1 or 2, wherein the metal oxide as the acceptor is a metal oxide capable of forming a charge transfer complex. The organic electroluminescent element according to any one of claims 1 to 3 , wherein the metal oxide is molybdenum oxide or vanadium oxide. The organic electroluminescent device according to claim 4 , wherein the organic compound is 7,7,8,8-tetrafluorotetracyanoquinodimethane.