JPH11111463A - Organic electroluminescence device - Google Patents

Abstract

[PROBLEMS] To provide a long-life organic electroluminescent element having excellent stability of electric characteristics at the time of driving without impairing characteristics of high luminance, high luminous efficiency, and low driving voltage. An organic electroluminescent device having an organic layer containing a light emitting material and an organic layer containing a hole transport material between an anode and a cathode, at least one of which is transparent or translucent, comprises: An organic electroluminescence device in which at least one of the organic layers containing the material contains an electron accepting compound having an electron affinity of 1.0 eV or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic electroluminescence device (hereinafter, sometimes referred to as an organic EL device).

[0002]

2. Description of the Related Art Inorganic electroluminescent elements (hereinafter sometimes referred to as inorganic EL elements) using an inorganic phosphor as a light emitting material are used, for example, in a planar light source as a backlight or a display device such as a flat panel display. However, a high voltage AC was required to emit light.

[0003] In recent years, Tang et al. Have proposed a two-layered organic E layer having an organic fluorescent dye as a light-emitting layer and an organic charge transport compound used for an electrophotographic photoreceptor.
An L element was produced (JP-A-59-194393). Compared to inorganic EL elements, organic EL elements are characterized by low voltage driving, high luminance, and easy emission of many colors. Attempts have been reported [Japanese Journal of Applied Physics (Jpn. J. Appl. Phys.) 27
Volume, page L269 (1988), Journal of Applied Physics (J. Appl. Phys.).
65, 3610 (1989)].

Further, as a high molecular weight light emitting material, WO
JP-A-9013148, JP-A-3-244630
Publication, Applied Physics Letters (App
l. Phys. Lett. Vol. 58, p. 1982 (1
991). WO9013148
In the examples disclosed in the specification of Japanese Patent Application Laid-Open Publication No. H10-186, a poly (p-phenylenevinylene) thin film converted into a conjugated polymer is obtained by forming a soluble precursor on an electrode and performing a heat treatment. The disclosed organic EL device is disclosed.

Further, JP-A-3-244630 exemplifies a conjugated polymer having a feature that it is soluble in a solvent itself and does not require heat treatment. Applied Physics Letters (Appl.
s. Lett. Vol. 58, p. 1982 (1991)
Also describes a polymer light-emitting material soluble in a solvent and an organic EL device manufactured using the same.

Further, an organic EL device in which a hole transporting material layer is laminated in addition to a light emitting layer is known (for example, described in JP-A-3-27387). However, there has been a demand for an organic EL device having an excellent stability of electric characteristics and a longer life.

Further, Japanese Patent Application Laid-Open No. Hei 6-220439 discloses that
An organic EL device using a metal complex having at least one quinolinato compound and at least one electron-accepting compound and / or electron-donating compound in the same layer is described. Japanese Patent Application Laid-Open No. 9-59614 discloses an organic EL device in which a light emitting layer contains a polymer fluorescent substance and one or more kinds of electron-accepting and / or electron-donating organic compounds. It is described that a layer in which a charge transporting material (which is a general term of an electron transporting material and a hole transporting material) is dispersed in a polymer compound can be used (page 11, lines 19 to 22). Line).

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a long-life organic electroluminescent device having excellent stability of electric characteristics at the time of driving without impairing characteristics of high luminance, high luminous efficiency and low driving voltage. Is to provide.

[0009]

Means for Solving the Problems The present inventors have made intensive studies in view of such circumstances, and as a result, by using a specific electron-accepting compound in combination with a hole transporting material, high brightness and high luminescence have been achieved. Without sacrificing efficiency and low drive voltage
The present inventors have found that a long-life organic EL device having excellent stability of electric characteristics can be obtained, and have reached the present invention.

That is, the present invention relates to an organic electroluminescent device having an organic layer containing a light emitting material and an organic layer containing a hole transport material between an anode and a cathode, at least one of which is transparent or translucent. The present invention relates to an organic electroluminescence device in which at least one of the organic layers containing the hole transport material contains an electron accepting compound having an electron affinity of 1.0 electron volt or more.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the organic EL device of the present invention will be described in detail. The organic EL device of the present invention is an organic EL device having an organic layer containing a light emitting material and an organic layer containing a hole transport material between an anode and a cathode, at least one of which is transparent or translucent. When the number of the organic layers containing the hole transport material is one, the layer has an electron affinity of 1 or more when the number of the organic layers containing the hole transport material is two or more. It is characterized by containing an electron-accepting compound of not less than 0.0 electron volts.

As an organic EL device of the present invention, an organic layer containing a luminescent material and an organic layer containing a hole transport material are provided between a cathode and an anode in the stated order from the cathode to the anode. Organic EL elements are preferred because of their high luminous efficiency.
The organic layer containing the light emitting material and the organic layer containing the hole transporting material may be used independently in two or more layers. When a plurality of layers are used, there is no particular limitation on the relative positions of the same type of layers, and the layers can be appropriately used in consideration of luminous efficiency and element life.

Further, as the organic EL device of the present invention, an organic EL device having an organic layer containing an electron transporting material between a cathode and an anode is preferable because of high luminous efficiency. In particular, as the organic EL device of the present invention, between the cathode and the anode, from the cathode toward the anode, an organic layer containing an electron transport material,
An organic EL element having an organic layer containing a light emitting material and an organic layer containing a hole transporting material in the stated order is preferable because of high luminous efficiency. The organic layer containing the light emitting material, the organic layer containing the hole transporting material, and the organic layer containing the electron transporting material may be independently used in two or more layers. Also,
When a plurality of layers are used, the relative positions of the same type of layers are not particularly limited, and the layers can be appropriately used in consideration of light emission efficiency and device life. In the organic EL device of the present invention, it is highly preferable that an organic layer containing an electron transporting material is provided between the organic layer containing the luminescent material and the cathode, adjacent to the organic layer containing the luminescent material. It is more preferable because of luminous efficiency.

In the organic EL device of the present invention, the electron-accepting compound used together with the hole transporting material must have an electron affinity of 1.0 eV or more, and 1.5 eV or more. Preferably, it is 2.0 eV or more. When the electron affinity is less than 1.0 electron volt, the effect of the present invention is insufficient, which is not preferable.

The electron affinity is absolute zero, the energy generated when negative ions are generated by the reaction between a neutral molecule and a thermoelectron in the gas phase. If this value is positive, the generated negative ions are neutral. It is more stable than the state.
The electron affinity is determined by the molecular crystal and liquid crystal (Mol. Cryst. Li).
q. Cryst. ) Vol. 171, p. 271 (1989)
Year), magnetron method, electron capture detector method, alkali metal
It can be measured using a beam method, a thermal charge transfer method, a half-wave reduction potential method, or the like. In the present invention, the electron affinity indicates a value measured by using a half-wave reduction potential method.

As the electron-accepting compound used in the present invention, known compounds can be used, and compounds having a nitro group, halogen, cyano group, trifluoromethyl group and the like as substituents, quinone compounds, acid anhydride compounds , Fullerene and the like.

Specifically, hexacyanobutadiene, hexacyanobenzene, tetracyanoethylene, tetracyanoquinodimethane, tetrafluorotetracyanoquinodimethane, p-fluoranyl, p-chloranyl, 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,
2,4,7-trinitro-9-fluorenone, 2,3
5,6-tetracyanopyridine, maleic anhydride, phthalic anhydride, C ₆₀ , C _{70 and the} like are exemplified.

Of these, hexacyanobutadiene, hexacyanobenzene, tetracyanoethylene, tetracyanoquinodimethane, tetrafluorotetracyanoquinodimethane, p-fluoranyl, p-chloranyl, p-bromanyl, p-benzoquinone, 2,6-dichloro Benzoquinone, 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-fluorenone , 2,
3,5,6-tetramethyl-cyanopyridine, C ₆₀ are preferred,
Hexacyanobutadiene, hexacyanobenzene, tetracyanoethylene, tetracyanoquinodimethane, tetrafluorotetracyanoquinodimethane, p-fluoranyl, p-chloranyl, p-bromanyl, 2,6-dichlorobenzoquinone, 2,5-dichlorobenzoquinone, 2,
3-Dichloronaphthoquinone, 1,2,4,5-tetracyanobenzene, 2,3-dichloro-5,6-dicyanobenzoquinone and 2,3,5,6-tetracyanopyridine are particularly preferred.

These electron accepting compounds may be used alone or in combination of two or more. The amount of the electron-accepting compound used depends on the type of the material, but at least one of the organic layers containing the hole-transporting material contains the electron-accepting compound in an amount of 0.01% by weight or more based on the hole-transporting material. 5
0 wt% or less, preferably 0.1 wt% or more
% By weight or less, more preferably 0.2% by weight or more and 10% by weight or less. When the amount of the organic compound used in the organic layer containing the hole transport material is 0.
When the amount is less than 01% by weight, the effect of the present invention is insufficient, so that it is not preferable. When the amount exceeds 50% by weight, the hole transporting ability is impaired.

The hole transporting material used in the present invention includes pyrazoline derivatives, arylamine derivatives, stilbene derivatives, triphenyldiamine derivatives, polyvinylcarbazole or its derivatives, polyaniline or its derivatives, polythiophene or its derivatives, and poly (p
-Phenylenevinylene) or a derivative thereof, or poly (2,5-thienylenevinylene) or a derivative thereof.

Specifically, examples of the hole transport material include JP-A-63-70257, JP-A-63-175860, JP-A-2-135359 and JP-A-2-13536.
No. 1, JP-A-2-209988, JP-A-3-3799
No. 2, JP-A-3-152184, etc. are exemplified.

As the hole transporting material, triphenyldiamine or a derivative thereof, polyvinyl carbazole or a derivative thereof, a conjugated polymer, polyaniline, or the like is preferable, and 4,4′-bis (N (3
-Methylphenyl) -N-phenylamino) biphenyl, or polyvinylcarbazole or a derivative thereof.

The method of mixing the hole transporting material and the electron accepting compound is not limited. For the low molecular weight hole transporting material, a method of co-evaporation by vacuum evaporation, mixed evaporation, or film formation from a mixed solution is used. Is exemplified. When forming a film from a solution, a polymer binder may be used in combination. In the case of a polymer hole transport material, a method of forming a film from a mixed solution is exemplified.

The solvent used for film formation from a solution needs to dissolve the hole transport material and the electron accepting compound.
Specifically, as the solvent, chlorinated solvents such as chloroform, methylene chloride and dichloroethane, ether solvents such as tetrahydrofuran, aromatic hydrocarbon solvents such as toluene and xylene, ketone solvents such as acetone and methyl ethyl ketone, and acetic acid Ester solvents such as ethyl, butyl acetate, and ethyl cellose acetate are exemplified.

As a method for forming a film from a solution, a microgravure coating method, a gravure coating method, a bar coating method, a roll coating method, a wire bar coating method, a dip coating method, a spray coating method, a spin coating method, a screen coating method, etc. Printing methods, flexographic printing methods, offset printing methods, and the like can be given.

As the polymer binder, those which do not extremely inhibit charge transport are preferable, and those which do not strongly absorb visible light are suitably used. Examples of the polymer binder include polycarbonate, polyacrylate, polymethyl acrylate, polymethyl methacrylate, polystyrene, polyvinyl chloride, and polysiloxane.

Next, the organic EL device of the present invention will be described in more detail. As the light emitting material contained in the organic layer containing the light emitting material of the organic EL device in the present invention, known materials can be used. Examples of low molecular weight compounds include naphthalene derivatives, anthracene or derivatives thereof, perylene or derivatives thereof, polymethine-based, xanthene-based, coumarin-based, cyanine-based dyes, metal complexes of 8-hydroxyquinoline or derivatives thereof, and aromatic amines. , Tetraphenylcyclopentadiene or a derivative thereof, or tetraphenylbutadiene or a derivative thereof can be used. Specifically, known materials such as those described in JP-A-57-51781 and JP-A-59-194393 can be used.

Further, as the light emitting material contained in the organic EL device of the present invention, a polymeric fluorescent substance is preferable, and the light emitting material contains a repeating unit represented by the following formula (1) in an amount of 50 mol% or more of all repeating units, and A polymeric fluorescent substance having a converted number average molecular weight of 10 ³ to 10 ⁷ is preferable.

[0029]

Embedded image -Ar-CR = CR′- (1) [where Ar has 6 carbon atoms involved in a conjugate bond.
An arylene group comprising at least 20 but no more than 20 or a heterocyclic compound group comprising at least 4 but no more than 20 carbon atoms involved in a conjugated bond. R and R 'each independently represent a group selected from the group consisting of hydrogen, an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, a heterocyclic compound group having 4 to 20 carbon atoms, and a cyano group. Show. ]

Although it depends on the structure of the repeating unit, the repeating unit represented by the formula (1) is 70% of all repeating units.
More preferably, it is at least mol%. The polymeric fluorescent substance can be obtained by using a divalent aromatic compound group or a derivative thereof, a divalent heterocyclic compound group or a derivative thereof, or a combination thereof as a repeating unit other than the repeating unit represented by the formula (1). May be included. Further, the repeating unit represented by the formula (1) or another repeating unit may be linked by a non-conjugated unit having an ether group, an ester group, an amide group, an imide group, or the like, A non-conjugated moiety may be included.

When the light emitting material is a polymeric fluorescent substance containing a repeating unit of the formula (1), Ar in the formula (1) is an arylene group having 6 to 20 carbon atoms involved in a conjugate bond. Or when the number of carbon atoms involved in the conjugate bond is 4
A heterocyclic compound group comprising at least 20 but no more than 20 divalent aromatic compound groups or derivatives thereof represented by the following chemical formulas 3 to 5, a divalent heterocyclic compound group or a derivative group thereof,
Or groups obtained by combining them are exemplified.

[0032]

Embedded image

[0033]

Embedded image

[0034]

Embedded image (R _{1 to} R ₉₂ each independently represent hydrogen, carbon number 1 to 2
0 alkyl, alkoxy and alkylthio groups;
An aryl group and an aryloxy group having 6 to 18 carbon atoms;
And a group selected from the group consisting of heterocyclic compound groups having 4 to 14 carbon atoms. )

Of these, phenylene, substituted phenylene, biphenylene, substituted biphenylene, naphthalenediyl, substituted naphthalenediyl, anthracene-9,10-diyl, substituted anthracene-9,10
-Diyl, pyridine-2,5-diyl, substituted pyridine-2,5-diyl, thienylene or substituted thienylene are preferred. More preferably, a phenylene group,
Biphenylene group, naphthalenediyl group, pyridine-2,
It is a 5-diyl group or a thienylene group.

In the case where R and R 'in the formula (1) are hydrogen or a substituent other than a cyano group, the number of carbon atoms is one.
Examples of the alkyl group of 20 include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a decyl group, a lauryl group, and the like, and a methyl group, an ethyl group, a pentyl group, Hexyl, heptyl and octyl groups are preferred.

The aryl group in R, R 'of the formula (1) include a phenyl group, 4-C ₁ -C _{1 2} alkoxyphenyl group (C ₁ -C ₁₂ indicates that it is 1 to 12 carbon atoms . the same applies is _{less.), 4-C 1 ~C} 12 alkyl phenyl group, 1-naphthyl group, 2-naphthyl groups. Examples of the aryloxy group in R and R ′ in the formula (1) include a phenoxy group.

Examples of the heterocyclic compound group represented by R and R 'in the formula (1) include a 2-thienyl group, a 2-pyrrolyl group, a 2-furyl group, a 2-, 3- or 4-pyridyl group and the like. .

From the viewpoint of solvent solubility, Ar of the formula (1)
Is selected from the group consisting of one or more alkyl groups having 4 to 20 carbon atoms, alkoxy groups and alkylthio groups, aryl groups and aryloxy groups having 6 to 18 carbon atoms, and heterocyclic compound groups having 4 to 14 carbon atoms. It is preferred to have a substituent.

The following are examples of the substituent of Ar in the formula (1). Examples of the alkyl group having 4 to 20 carbon atoms include a butyl group, a pentyl group, a hexyl group, a heptyl group,
Examples thereof include an octyl group, a decyl group, and a lauryl group, and a pentyl group, a hexyl group, a heptyl group, and an octyl group are preferable.

Examples of the alkoxy group having 4 to 20 carbon atoms include a butoxy group, a pentyloxy group, a hexyloxy group, a heptyloxy group, an octyloxy group, a decyloxy group and a lauryloxy group. Hexyloxy, heptyloxy and octyloxy groups are preferred.

As the alkylthio group, a butylthio group,
Examples include a pentylthio group, a hexylthio group, a heptylthio group, an octylthio group, a decyloxy group, and a laurylthio group. A pentylthio group, a hexylthio group, a heptylthio group, and an octylthio group are preferable. Examples of the aryl group include a phenyl group, 4-C ₁ ~C ₁₂ alkoxyphenyl group, 4-C ₁ ~C ₁₂ alkyl phenyl group, 1-naphthyl group, 2-naphthyl group. Examples of the aryloxy group include a phenoxy group. Examples of the heterocyclic compound group include a 2-thienyl group, a 2-pyrrolyl group, a 2-furyl group, a 2-, 3- or 4-pyridyl group, and the like.

The preferred number of these substituents varies depending on the molecular weight of the polymeric fluorescent substance and the constitution of the repeating unit. However, from the viewpoint of obtaining a polymeric fluorescent substance having high solubility, these substituents are used per 600 molecular weight. Preferably, the number is one or more. When the luminescent material is a polymeric fluorescent substance, the above-mentioned luminescent material other than the polymeric fluorescent substance may be mixed and used in the organic layer containing the luminescent material. The method for synthesizing the polymeric fluorescent substance is not particularly limited, and examples thereof include a method described in JP-A-5-202355.

The polymeric fluorescent substance may be a random, block or graft copolymer, or a polymer having an intermediate structure between them, for example, a random copolymer having a block property. You may. From the viewpoint of obtaining a polymeric fluorescent substance having a high quantum yield of fluorescence, a random copolymer having block properties or a block or graft copolymer is preferable to a complete random copolymer. In addition, since light emission from a thin film is used, a polymer fluorescent substance having fluorescence in a solid state is preferably used.

As a good solvent for the polymeric fluorescent substance,
Examples thereof include chloroform, methylene chloride, dichloroethane, tetrahydrofuran, toluene, xylene, mesitylene, decahydronaphthalene, butylbenzene, and methyl isobutyl ketone. Although depending on the structure and molecular weight of the polymeric fluorescent substance, the polymeric fluorescent substance can be generally dissolved in these solvents in an amount of 0.1% by weight or more.

The polymeric fluorescent substance preferably has a number average molecular weight of 10 ³ to 10 ⁷ in terms of polystyrene. The degree of polymerization also depends on the type of repeating structure and its ratio. In general, the total number of repeating structures is preferably from 4 to 10,000, more preferably from 5 to 5 from the viewpoint of film formability.
3000, particularly preferably 10-2000.

When these polymer fluorescent materials are used as a light emitting material for an organic EL device, their purity affects the light emitting characteristics. Therefore, after the synthesis, purification treatment such as reprecipitation purification, fractionation by chromatography, etc., may be required. preferable.

When a film is formed from a solution by using these organic solvent-soluble polymer fluorescent materials in the preparation of an organic EL device, it is only necessary to remove the solvent by drying after coating this solution. The same method can be applied to a case where a transport material and a light-emitting material are mixed, which is very advantageous in production. Examples of the method of forming a film from a solution include a microgravure coating method, a gravure coating method, a bar coating method, a roll coating method, a wire bar coating method, a dip coating method, a spray coating method, a spin coating method, a screen printing method, and a flexographic printing method. And an offset printing method.

Further, a layer in which the polymeric fluorescent substance and / or the charge transporting material is dispersed in a polymeric binder may be used.

In the present invention, when the organic EL device has an organic layer containing an electron transporting material, a known electron transporting material can be used, such as an oxadiazole derivative, anthraquinodimethane or an oxadiazole derivative. Derivative, benzoquinone or its derivative, naphthoquinone or its derivative, anthraquinone or its derivative, tetracyanoanthraquinodimethane or its derivative, fluorenone derivative, diphenyldicyanoethylene or its derivative, diphenoquinone derivative, or metal of 8-hydroxyquinoline or its derivative Complexes are exemplified.

Specifically, JP-A-63-70257 and JP-A-63-175860, and JP-A-2-1353
Nos. 59, 2-135361, 2-209
988, 3-37992, 3-152
No. 184 is exemplified.

Of these, oxadiazole derivatives,
Benzoquinone or a derivative thereof, anthraquinone or a derivative thereof, or a metal complex of 8-hydroxyquinoline or a derivative thereof is preferable, and 2- (4-biphenylyl) -5- (4-t-butylphenyl) -1,3,3 is preferable.
4-oxadiazole, benzoquinone, anthraquinone, and tris (8-quinolinol) aluminum are more preferred.

The method of forming the organic layer containing the electron transporting material is not particularly limited. For the low molecular weight electron transporting material, a method of vacuum deposition from a powder or a method of forming a film from a solution or a molten state is used. In the case of the polymer electron transport material, a method of forming a film from a solution or a molten state is exemplified. When forming a film from a solution or a molten state, a polymer binder may be used in combination.

The solvent used for film formation from a solution is not particularly limited as long as it can dissolve the electron transport material and / or the polymer binder. As the solvent, chloroform, methylene chloride, chlorine solvents such as dichloroethane, ether solvents such as tetrahydrofuran, aromatic hydrocarbon solvents such as toluene and xylene, acetone, ketone solvents such as methyl ethyl ketone, ethyl acetate, butyl acetate, Ester solvents such as ethylcellose acetate are exemplified.

As a film forming method from a solution or a molten state, a microgravure coating method, a gravure coating method, a bar coating method, a roll coating method, a wire bar coating method,
Examples include a dip coating method, a spray coating method, a spin coating method, a screen printing method, a flexographic printing method, and an offset printing method.

As the polymer binder to be mixed, those which do not extremely inhibit the charge transport are preferable, and those which do not strongly absorb visible light are preferably used. As the polymer binder, poly (N-vinylcarbazole), polyaniline or a derivative thereof, polythiophene or a derivative thereof, poly (p-phenylenevinylene) or a derivative thereof, poly (2,5-thienylenevinylene) or a derivative thereof, polycarbonate , Polyacrylate, polymethyl acrylate, polymethyl methacrylate, polystyrene, polyvinyl chloride, or polysiloxane.

In the present invention, a transparent or translucent anode
Materials include conductive metal oxide films, translucent metals
A thin film or the like is used. Specifically, indium tin
Oxide (ITO), ZnO, tin oxide (SnO)_Two)
Film made using conductive glass made of such as, gold,
Platinum, silver, copper, etc. are used, and ITO, ZnO, SnO _Two
Is preferred. Manufacturing methods include vacuum evaporation and sputtering
Method, ion plating method, plating method, etc.
You. In addition, an organic transparent material such as polyaniline is used as the anode.
A light conductive film may be used.

Next, as the material of the cathode used in the present invention, a material having a small ionization energy is preferable. For example, aluminum, indium, magnesium, calcium, lithium, magnesium-silver alloy, magnesium-indium alloy, lithium-aluminum alloy, lithium-silver alloy, lithium-indium alloy, calcium-aluminum alloy, graphite thin film and the like are used.

As a method for producing the cathode, a vacuum evaporation method, a sputtering method, a lamination method for thermocompression bonding a metal thin film, and the like are used. After the cathode is formed, a protective layer for protecting the organic EL device may be provided.

[0060]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples, but it should not be construed that the present invention is limited thereto. Here, regarding the number average molecular weight, the number average molecular weight in terms of polystyrene was determined by gel permeation chromatography (GPC) using chloroform as a solvent. The value of the electron affinity was measured by the half-wave reduction potential method, and the molecular crystal and liquid crystal (Mo)
l. Cryst. Liq. Cryst. ) Seventeenth
1 and p. 271 (1989).

Example 1 <Synthesis of polymeric fluorescent substance 1> 2,5-dioctyloxy-
p-Xylylene dichloride was reacted with triphenylphosphine in N, N-dimethylformamide solvent to synthesize a phosphonium salt. The resulting phosphonium salt 4
7.75 parts by weight and 5.5 parts by weight of terephthalaldehyde were dissolved in a mixed solvent of ethyl alcohol / chloroform. An ethyl alcohol solution containing 5.4 parts by weight of lithium ethoxide was added dropwise to a mixed solution of a phosphonium salt and dialdehyde in ethyl alcohol / chloroform to polymerize. Subsequently, a chloroform solution of 1-pyrenecarbaldehyde was added to the reaction solution, and then an ethyl alcohol solution containing lithium ethoxide was added dropwise to the reaction solution, followed by polymerization at room temperature for 3 hours. After standing at room temperature overnight, the precipitate was separated by filtration, washed with ethyl alcohol, dissolved in chloroform, and ethanol was added thereto to reprecipitate.
This was dried under reduced pressure to obtain 8.0 parts by weight of a polymer. This is called polymeric fluorescent substance 1. The repeating units of polymeric fluorescent substance 1 calculated from the charged ratio of the monomers and the molar ratios thereof are shown below. ¹ in that it has a pyrenyl group at the molecular terminal H
-Confirmed by NMR.

[0062]

Embedded image (In the above formula, the molar ratio of the two repeating units is 5
0:50, and the two repeating units are alternately linked. The polystyrene-equivalent number average molecular weight of the polymeric fluorescent substance 1 was 4.0 × 10 ³ . The structure of the polymeric fluorescent substance 1 was confirmed by an infrared absorption spectrum and ¹ H-NMR.

<Preparation and Evaluation of Device> 1.0% by weight of poly (N-vinylcarbazole) (hereinafter sometimes referred to as PVCz) and 0% of tetracyanoethylene (electron affinity: 2.9 electron volts) were used. A methylene chloride solution containing 0.011% by weight was prepared. This solution contains 1.0% by weight of tetracyanoethylene, which is an electron accepting compound, based on PVCz, which is a hole transport material. Using a methylene chloride solution of PVCz, a film was formed to a thickness of 60 nm by dip coating on a glass substrate provided with an ITO film having a thickness of 200 nm by electron beam evaporation. Next, using a 1.0% by weight toluene solution of the polymeric fluorescent substance 1, a film was formed to a thickness of 40 nm by spin coating. Then
After drying this under reduced pressure at 120 ° C. for 1 hour, tris (8-quinolinol) aluminum (hereinafter sometimes referred to as Alq ₃ ) is formed as an organic layer containing an electron transporting material.
Was deposited at a rate of 0.1 to 0.2 nm / s to a thickness of 40 nm.
Finally, as a cathode, an aluminum-lithium alloy (Al: Li = about 200: 1 weight ratio) was deposited to a thickness of 100 nm to produce an organic EL device. The degree of vacuum at the time of vapor deposition was 1 × 10 ⁻⁵ Torr or less.

The device was continuously driven at a constant current density of 25 mA / cm ² in a nitrogen atmosphere under a constant current. 20
The luminance after time aging is 464 cd / m ² , and the luminance after 50 hours of driving after aging is 32
It was 1 cd / m ² , and the extrapolated value of the half life from the luminance after aging for 20 hours was about 90 hours. Also, 20
The rate of increase in drive voltage during drive after time aging was 0.044 V / hr.

Example 2 <Production and evaluation of device> An organic EL device was produced in the same manner as in Example 1 except that the concentration of tetracyanoethylene added to the methylene chloride solution was changed to 0.025% by weight.
This solution contains 2.5% by weight of tetracyanoethylene, an electron accepting compound, based on PVCz, a hole transport material.
Including.

The device was driven in the same manner as in Example 1. The luminance after aging for 20 hours is 526.
a cd / m ^2, the luminance of 50 hours after the drive from the aging is 397cd / m ^2, extrapolated half life from the luminance after 20 hours aging was about 150 hours. The rate of increase in the driving voltage during driving after aging for 20 hours was 0.037 V / hr.

Example 3 <Preparation and evaluation of device> Instead of tetracyanoethylene added to a methylene chloride solution of PVCz, 2,3-
An organic EL device was produced in the same manner as in Example 1, except that dichloro-4,5-dicyanobenzoquinone (electron affinity: 3.2 eV) was used. This solution contains 1.0% by weight of 2,3-dichloro-4,5-dicyanobenzoquinone, which is an electron accepting compound, based on PVCz, which is a hole transporting material.

The device was driven in the same manner as in Example 1. The luminance after aging for 20 hours is 51
A 3 cd / m ^2, the luminance of 50 hours after the drive from the aging is 375cd / m ^2, extrapolated half life from the luminance after 20 hours aging, it was about 92 hours. The rate of increase in drive voltage during drive after aging for 20 hours was 0.063 V / hr.

Comparative Example 1 <Production and Evaluation of Element> An organic EL element was produced in the same manner as in Example 1 except that an electron-accepting compound was not added to a methylene chloride solution of PVCz.

The device was driven in the same manner as in Example 1. The luminance after aging for 20 hours is 46
A 7cd / m ^2, the luminance of 50 hours after the drive from the aging is 316cd / m ^2, extrapolated half life from the luminance after 20 hours aging was about 80 hours. The rate of increase in the driving voltage during driving after aging for 20 hours was 0.088 V / hr.

As is clear from the comparison between Examples 1 to 3 and Comparative Example 1, the organic EL device of the present invention can be used in combination with an electron-accepting compound in a constant current drive as compared with the case without the combined use. The driving voltage rise rate of the element was small, and the life was extended.

[0072]

The organic EL device of the present invention is a long-life organic electroluminescent device having excellent stability of electric characteristics at the time of driving without deteriorating characteristics of high luminance, high luminous efficiency and low driving voltage. . Therefore, the organic EL element can be preferably used as a device having a curved or planar light source as a backlight, a flat panel display, or the like.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Toshihiro Onishi 6 Kitahara, Tsukuba, Ibaraki Pref. Within Sumitomo Chemical Co., Ltd. (72) Inventor Yoichi Fukuda 5-9-5 Tokodai, Tsukuba, Ibaraki Pref. Stanley Electric Co., Ltd.

Claims (7)

[Claims] 1. An organic electroluminescent device comprising an organic layer containing a light emitting material and an organic layer containing a hole transport material between an anode and a cathode, at least one of which is transparent or translucent. An organic electroluminescent device, wherein at least one of the organic layers containing a transport material contains an electron-accepting compound having an electron affinity of 1.0 eV or more. 2. An organic layer containing a luminescent material and an organic layer containing a hole transporting material between a cathode and an anode in the stated order from the cathode to the anode. Item 2. The organic electroluminescent device according to Item 1. 3. The organic electroluminescent device according to claim 1, further comprising an organic layer containing an electron transporting material between the cathode and the anode. 4. An organic layer containing an electron transporting material, an organic layer containing a luminescent material, and an organic layer containing a hole transporting material are provided between the cathode and the anode, from the cathode to the anode. 4. The organic electroluminescent device according to claim 3, wherein the organic electroluminescent device is provided in order. 5. An organic layer containing an electron transporting material is provided between an organic layer containing a light emitting material and a cathode, adjacent to the organic layer containing the light emitting material.
Or the organic electroluminescent device according to 4. 6. An organic layer containing a hole transporting material, wherein at least one layer is a layer containing an electron accepting compound in an amount of 0.01 to 50% by weight based on the hole transporting material. The organic electroluminescence device according to claim 1. ^7. A polymeric fluorescent substance wherein the luminescent material contains a repeating unit represented by the following formula (1) in an amount of 50 mol% or more of all repeating units and has a polystyrene equivalent number average molecular weight of 10 ³ to 10 ^7. The organic electroluminescent device according to claim 1, wherein: Embedded image -Ar-CR = CR′- (1) [where Ar has 6 carbon atoms involved in a conjugate bond.
An arylene group comprising at least 20 but no more than 20 or a heterocyclic compound group comprising at least 4 but no more than 20 carbon atoms involved in a conjugated bond. R and R 'each independently represent a group selected from the group consisting of hydrogen, an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, a heterocyclic compound group having 4 to 20 carbon atoms, and a cyano group. Show. ]