JPH0935871A - Organic electroluminescence device - Google Patents

Abstract

(57) [Abstract] (Correction) [PROBLEMS] To provide an inexpensive organic electroluminescence device having high brightness, low driving voltage, high efficiency. In an organic electroluminescence device having at least a light emitting layer between electrodes composed of a pair of an anode and a cathode, at least one of which is transparent or semitransparent, the cathode in contact with the light emitting layer is composed of three or more metal layers,
The three metal layers are laminated in order of a light emitting layer, a first metal layer, a second metal layer, and a third metal layer, and the first metal layer in contact with the light emitting layer has a work function of 3 A metal of more than 0.7 eV and a thickness of 20 nm or less, the second metal layer of a metal having a work function of 3.7 eV or less, and the third metal layer of platinum, silver, gold or nickel. An organic electroluminescence device comprising a metal selected from titanium, tantalum, indium, and aluminum.

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 devices (hereinafter, sometimes referred to as inorganic EL devices) using an inorganic phosphor as a light emitting material are used for display devices such as a planar light source as a backlight and a flat panel display. However, a high-voltage alternating current was required to emit light. Recently, Tang et al. Used organic fluorescent dye as a light emitting layer,
An organic EL device having a two-layer structure was produced by laminating this and an organic charge transport compound used for electrophotographic photoreceptors and the like (JP-A-59-194393). Organic E
Compared to inorganic EL devices, L devices are characterized by low voltage drive, high brightness, and the ability to easily emit light of multiple colors. Therefore, many attempts have been made on device structures, organic fluorescent dyes, and organic charge transport compounds. Has been reported [Japanese Journal of Applied Physics (Jp
n. J. Appl. Phys. ) Volume 27, L269 (1988)], [Journal of Applied.
Physics (J. Appl. Phys.) Volume 65,
3610 (1989)].

Heretofore, low-molecular-weight organic fluorescent dyes have been generally used as a material for the light-emitting layer.
Examples of the high molecular weight light emitting material include WO901148, JP-A-3-244630, and Applied Physics Letters (Appl. Phys. Le).
tt. Vol. 58, p. 1982 (1991). In the examples disclosed in WO 9013148, 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 EL element is disclosed. JP-A-3-244630 exemplifies a conjugated polymer which is soluble in a solvent itself and does not require heat treatment. Applied Physics Letters (Appl.
Phys. Lett. 58, 1982 (199)
1 year) also describes a polymer light-emitting material soluble in a solvent and an organic EL device prepared using the same. But,
The organic EL device produced using these materials did not always have sufficiently high luminous efficiency.

Regarding the cathode of the organic EL element, an organic EL element using a metal having a small work function such as magnesium, lithium, or calcium as the metal material of the cathode is disclosed in Japanese Patent Application Laid-Open No. Hei 5 (1999) -58.
-101892, 1598881, 129080, 412
No. 81 publication.

However, the above-mentioned materials having a low work function and high electron injection efficiency such as magnesium, calcium, and lithium have a problem that they have high activity and easily react with moisture and oxygen in the air. In addition, in order to improve the adhesiveness with the organic layer, it was necessary to alloy and use it by co-evaporation with a stable metal such as silver or aluminum.
In such co-deposition, there is a problem that the efficiency is lowered depending on the deposition conditions, and it cannot be a low-cost industrial manufacturing process.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an inexpensive organic electroluminescence device having high brightness, low driving voltage, high efficiency.

[0007]

In view of the above circumstances, the inventors of the present invention have made diligent studies on the cathode material in order to improve the luminous efficiency of the organic EL element. As a result, the cathode of the organic EL element has two or more layers. It was found that the organic electroluminescence device improved in the maximum brightness and light emission efficiency of the organic EL device, the electrode manufacturing method was easy, and the device characteristic stability was improved by manufacturing by laminating the specific metal The present invention has been reached.

That is, the present invention is the invention described below. [1] In an organic electroluminescent device having at least a light emitting layer between an electrode composed of a pair of an anode and a cathode, at least one of which is transparent or semitransparent, the cathode in contact with the light emitting layer is composed of two or more metal layers, The two metal layers are laminated in order of the light emitting layer, the first metal layer, and the second metal layer, and the first metal layer in contact with the light emitting layer is made of a metal having a work function of more than 3.7 eV. , And 20 nm
And the work function of the second metal layer is 3.7.
An organic electroluminescence device comprising a metal having an eV or less. [2] In an organic electroluminescence device having at least a light emitting layer between an electrode composed of a pair of an anode and a cathode, at least one of which is transparent or semitransparent, the cathode in contact with the light emitting layer is composed of three or more metal layers, The three metal layers are laminated in the order of the light emitting layer, the first metal layer, the second metal layer, and the third metal layer, and the work function of the first metal layer in contact with the light emitting layer is 3. The second metal layer has a work function of 3.7 eV or less, and the third metal layer has a work function of 3.7 eV or less.
The organic electroluminescent device according to claim 1, wherein the metal layer is made of a metal selected from platinum, silver, gold, nickel, titanium, tantalum, indium or aluminum. [3] [1] or [2], wherein the first metal is a metal selected from platinum, silver, gold, nickel, titanium, tantalum, indium, aluminum, scandium, lead or zinc. Organic electroluminescent device. [4] The organic electroluminescence according to [1] to [3], wherein the second metal layer is made of a metal selected from lithium, strontium, calcium and magnesium or an alloy containing 0.01% or more thereof. element.

[5] The second metal layer is made of a lithium-aluminum alloy.
[3] The organic electroluminescence device as described above. [6] The light emitting layer contains a repeating unit having a conjugated structure as a main chain, and has a polystyrene reduced number average molecular weight of 10 ³ to 10 ⁷
The organic electroluminescence device according to [1] to [5], which contains a polymer having fluorescence in a solid state. [7] The polymer has a repeating unit represented by the formula (1):
7. The organic electroluminescence device according to claim 6, which contains 50 mol% or more of all repeating units.

[Image Omitted] -Ar-CR = CR'- (1) [wherein Ar has 4 carbon atoms involved in a conjugated bond.
Or more and 20 or less arylene group or heterocyclic compound group, R and R'each independently represent hydrogen, carbon number 1 to 2
A group selected from the group consisting of an alkyl group having 0, an aryl group having 6 to 20 carbon atoms, a heterocyclic compound having 4 to 20 carbon atoms, and a cyano group is shown. [8] The organic electroluminescent device according to [1] to [7], wherein a layer made of an electron transporting compound is provided between the cathode and the light emitting layer so as to be adjacent to the light emitting layer.

[9] The organic electroluminescence device according to [1] to [7], wherein a layer made of a hole transporting compound is provided between the anode and the light emitting layer, adjacent to the light emitting layer. [10] A layer composed of an electron transporting compound is provided between the cathode and the light emitting layer adjacent to the light emitting layer, and a hole transporting property is provided between the anode and the light emitting layer adjacent to the light emitting layer. An organic electroluminescence device according to any one of [1] to [7], which is provided with a layer made of a compound.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the organic EL device of the present invention will be described in detail. The organic EL element of the present invention is an organic electroluminescence element having at least a light emitting layer between an electrode composed of a pair of an anode and a cathode, at least one of which is transparent or semitransparent. (Including alloy) Layer.

The two metal layers are formed by laminating a light emitting layer, a first metal layer (which is in direct contact with the light emitting layer), and a second metal layer in this order. The first metal layer in contact with the light emitting layer is made of a metal having a work function of more than 3.7 eV and has a thickness of 20 nm or less. The second metal layer in contact with the first metal layer is made of a metal (including alloy) having a work function of 3.7 eV or less. Furthermore, in the organic EL device of the present invention, the cathode in contact with the light emitting layer is composed of three or more metal layers, and the three metal layers are the light emitting layer, the first metal layer, the second metal layer, and the third metal layer. The metal layers are laminated in this order. The first metal layer, the second
The metal layer of is the same as above, and the third metal layer is made of a metal selected from platinum, silver, gold, nickel, titanium, tantalum, indium or aluminum. Here, the metal used for the first metal layer has a work function of 3.7e.
There is no particular limitation as long as it exceeds V, but platinum, silver,
A metal selected from gold, nickel, titanium, tantalum, indium, aluminum, scandium, lead and zinc is preferable, and platinum, silver, gold, indium and aluminum are more preferable. The thickness of the first metal layer may be 20 nm or less, preferably 20 nm or less and 1 nm or more, and more preferably 10 nm or less and 2 nm or more.
Examples of the method for forming the first metal layer include a vapor deposition method and a sputtering method, but the vapor deposition method is preferable.

The metal used as the second metal layer of the cathode may be any metal (including alloy) having a work function of 3.7 eV or less, and specifically, lithium, strontium, calcium, magnesium, or these. And an alloy containing lithium, strontium, calcium, or an alloy containing these is preferable, and lithium or an alloy containing this is particularly preferable. When an alloy is used for the second metal layer, there is no particular limitation as long as it contains a metal having a work function of 3.7 eV or less, and the work function is 3.7.
Examples thereof include alloys of a metal of eV or less and silver, gold, platinum, aluminum, indium, or the like. Specifically, lithium aluminum alloy, lithium silver alloy, lithium indium alloy, potassium aluminum alloy, potassium silver alloy,
Examples thereof include potassium indium alloy. Composition ratio of the alloy (a metal having a work function of 3.7 eV or more and a work function of 3.
The composition ratio with a metal of 7 eV or less) has a work function of 3.7 in the entire cathode, that is, the first, second and third metal layers.
The composition ratio of the metal of eV or less is 0.005% or more and 99.9.
% Or less alloy is selected, and preferably 0.
005% or more and 10% or less, more preferably 1%
It is above 2%. The thickness is 10 nm or more and 100
It is preferably 0 nm or less, and more preferably 20 nm or more and 200 nm or less. Examples of the method for forming the second metal layer include a vapor deposition method and a sputtering method, but the vapor deposition method is preferable. For example, it can be manufactured by vapor deposition from a metal having a work function of 3.7 eV or less or an alloy containing the metal.

The third metal layer of the cathode is made of a noble metal that is resistant to oxidation or corrosion in air, a transition metal that forms an immovable body, or a metal or alloy having a small Young's modulus. Specifically, it is made of a metal thin film selected from platinum, silver, gold, indium and aluminum, and indium and aluminum are more preferable. As a method of forming the third metal layer of the cathode, a vapor deposition method after forming up to the second metal layer of the cathode,
Examples include a method of forming a metal thin film by a sputtering method, a method of sequentially forming a second metal layer of a cathode, a first metal layer of a cathode, an organic layer, a transparent electrode, etc. on a metal foil.
The vapor deposition method is preferred. The thickness of the third metal layer is not particularly limited, but when it is formed by a vapor deposition method, a sputtering method, or the like, if it is made too thin, the first metal layer or the second metal layer is sufficiently shielded from the outside air. Therefore, the thickness is preferably 50 nm or more, and more preferably 100 nm or more.

In the present invention, the light emitting material of the organic EL device is not particularly limited, and low molecular weight organic fluorescent dyes and high molecular weight fluorescent substances can be used, but high molecular weight fluorescent substances are preferred, and conjugated high molecular weight substances are also used. Is preferred. Among the conjugated polymers, those containing an arylene vinylene structure are particularly preferable. Examples of the low-molecular-weight light emitter include dyes such as naphthalene derivative, anthracene derivative, perylene derivative, polymethine type, xathene type, coumarin type, cyanine type, metal complex of 8-hydroquinoline and its derivative, aromatic amine, tetraphenylcyclo Pentadiene derivatives, etc. or JP-A-5
Known materials described in 7-51781 and 59-194393 can be used.

When a polymeric fluorescent substance is used as the light emitting layer of the organic EL device of the present invention, a polymer having a light emitting group in its side chain can be used, but preferably it contains a conjugated structure in its main chain. Especially, polythiophene, poly-p-phenylene, polyarylene vinylene and derivatives thereof are preferable. Of these, polyarylene vinylene and its derivatives are preferable. The polyarylene vinylene and its derivatives are polymers containing the repeating unit represented by the formula (1) in an amount of 50 mol% or more of all repeating units. Although it depends on the structure of the repeating unit, it is more preferable that the repeating unit represented by the formula (1) accounts for 70% or more of all repeating units. The polymeric fluorescent substance is obtained by combining a divalent aromatic compound group or a derivative thereof, a divalent heterocyclic compound group or a derivative thereof, and a combination thereof as a repeating unit other than the repeating unit represented by the formula (1). And the like. Further, the repeating unit represented by the formula (1) or another repeating unit may be linked with a non-conjugated unit having an ether group, an ester group, an amide group, an imide group or the like, A non-conjugated portion may be included.

In the polymeric fluorescent substance of the present invention, Ar of the formula (1) is an arylene group or a heterocyclic compound group having 4 to 20 carbon atoms involved in a conjugated bond, and A divalent aromatic compound group or a derivative group thereof, a divalent heterocyclic compound group or a derivative group thereof,
And groups and the like obtained by combining them.

[0017]

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. )

Among these, phenylene group, substituted phenylene group, biphenylene group, substituted biphenylene group, naphthalenediyl group, substituted naphthalenediyl group, anthracene-9,10-diyl group, substituted anthracene-9,10-
A diyl group, a pyridine-2,5-diyl group, a substituted pyridine-2,5-diyl group, a thienylene group and a substituted thienylene group are preferable. More preferably, phenylene group, biphenylene group, naphthalenediyl group, pyridine-2,5
A diyl group and a thienylene group.

In the formula (1), R and R'are hydrogen or a cyano group.
When the case of a substituent other than is described,
Examples of the alkyl group 20 include a methyl group, an ethyl group,
Pill, butyl, pentyl, hexyl, heptyl
Group, octyl group, decyl group, lauryl group, etc.
Methyl, ethyl, pentyl, hexyl,
A butyl group and an octyl group are preferred. As an aryl group
Is a phenyl group, 4-C₁~ C₁₂Alkoxyphenyl group
(C ₁~ C₁₂Indicates that the carbon number is 1 to 12. Less than
Is also the same. ), 4-C₁~ C₁₂Alkylphenyl
Group, 1-naphthyl group, 2-naphthyl group and the like.
You.

From the viewpoint of solvent solubility, Ar of the formula (1)
Is a group selected from 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 preferable to have.

Examples of these substituents are as follows. Examples of the alkyl group having 4 to 20 carbon atoms include a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a decyl group, and a lauryl group. 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. , A heptyloxy group and an octyloxy group. Examples of the alkylthio group having 4 to 20 carbon atoms include a butylthio group, a pentylthio group, a hexylthio group, a heptylthio group, an octylthio group, a decyloxy group and a laurylthio group, and a pentylthio group, a hexylthio group, a heptylthio group and an octylthio group are preferable. As the aryl group, a phenyl group, a 4-C ₁ -C ₁₂ alkoxyphenyl group, a 4-C ₁ -C ₁₂ alkylphenyl group, 1
Examples include -naphthyl group and 2-naphthyl group. Examples of the aryloxy group include a phenoxy group. Examples of the heterocyclic compound group include 2-thienyl group, 2-pyrrolyl group, 2-furyl group, 2-, 3- or 4-pyridyl group. The number of these substituents varies depending on the molecular weight of the polymeric fluorescent substance and the structure of the repeating unit, but from the viewpoint of obtaining a polymeric fluorescent substance having high solubility, these substituents are one or more per 600 molecular weight. Is more preferable.

The polymeric fluorescent substance used in the organic EL device of the present invention may be a random, block or graft copolymer, or a polymer having an intermediate structure between them, such as a block type polymer. It may be a random copolymer. 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. Further, since the organic EL device of the present invention utilizes light emission from a thin film, the polymeric fluorescent substance used is one having fluorescence in a solid state.

As a good solvent for the polymeric fluorescent substance,
Examples include chloroform, methylene chloride, dichloroethane, tetrahydrofuran, toluene, xylene and the like.
Although it depends on the structure and molecular weight of the polymeric fluorescent substance, it can be generally dissolved in these solvents in an amount of 0.1% by weight or more.

The polymeric fluorescent substance of the present invention preferably has a molecular weight of 10 ³ to 10 ⁷ in terms of polystyrene, and the degree of polymerization thereof varies depending on the repeating structure and the ratio thereof. From the viewpoint of film-forming property, generally, the total number of repeating structures is preferably 4 to 10,000, more preferably 5 to 300.
0, particularly preferably 10 to 2000.

When these organic solvent-soluble polymeric fluorescent substances are used to form an organic EL device, when a film is formed from a solution, it suffices to remove the solvent by coating the solution and then drying it. In addition, the same method can be applied when a charge transport material or a light emitting material is mixed, which is very advantageous in manufacturing.

The method for synthesizing the polymeric fluorescent substance used in the organic EL device of the present invention is not particularly limited. For example, a dialdehyde compound in which two aldehyde groups are bonded to an arylene group and a methyl halide group in an arylene group are used. An example is the Wittig reaction from a diphosphonium salt obtained from a compound having two bonds and triphenylphosphine.
Another example of a synthesis method is a dehydrohalogenation method from a compound in which two methyl halide groups are bonded to an arylene group. Further, a sulfonium salt decomposition method for obtaining a polymeric fluorescent substance by heat treatment from an intermediate obtained by polymerizing a sulfonium salt of a compound having two arylene groups and two halogenated methyl groups with an alkali is exemplified. In any of the synthesis methods, a compound having a skeleton other than the arylene group is added as a monomer, and the structure of the repeating unit contained in the resulting polymeric fluorescent substance can be changed by changing the proportion thereof. You may add and adjust so that the repeating unit shown by (1) may be 50 mol% or more, and may copolymerize. Of these, Wit
The method based on the tig reaction is preferable in terms of reaction control and yield.

More specifically, a method for synthesizing an arylene vinylene-based copolymer, which is one example of the polymeric fluorescent substance used in the organic EL device of the present invention, will be described. For example, Wit
When a polymeric fluorescent substance is obtained by the Tig reaction, for example, first, a bis (methyl halide) compound, more specifically, for example, 2,5-dioctyloxy-p-xylylene dibromide is added to N, N-dimethylformamide. In a solvent,
A phosphonium salt is synthesized by reacting with triphenylphosphine, and this and a dialdehyde compound, more specifically,
For example, the condensation of terephthalaldehyde with lithium ethoxide in, for example, ethyl alcohol, Wi
The phenylene vinylene group and 2,5-
A polymeric fluorescent substance containing a dioctyloxy-p-phenylenevinylene group is obtained. At this time, two or more kinds of diphosphonium salts and / or two or more kinds of dialdehyde compounds may be reacted to obtain a copolymer.

When these polymeric fluorescent substances are used as a light emitting material of an organic EL device, the purity thereof affects the light emitting characteristics, and therefore, after the synthesis, purification treatment such as reprecipitation purification and fractionation by chromatography can be performed. desirable.

Regarding the structure of the organic EL device of the present invention,
There is no particular limitation other than the above-mentioned features of the present invention, and a known structure is adopted. For example, a pair of electrodes is provided on both sides of a light emitting layer made of the polymeric fluorescent substance or a light emitting layer made of a mixture of the polymeric fluorescent substance and a charge transporting material (collective term of electron transporting material and hole transporting material). Examples of the structure having Moreover, the thing which provided the hole transport layer containing a hole transport material between the light emitting layer and an anode is mentioned. At this time, the hole transport layer is preferably adjacent to the light emitting layer. Further, an electron transport layer containing an electron transport material may be provided between the light emitting layer and the cathode. At this time, the electron transport layer is preferably adjacent to the light emitting layer. Furthermore, a hole transport layer containing a hole transport material is provided between the light emitting layer and the anode, and an electron transport layer containing an electron transport material is provided between the light emitting layer and the cathode. Further, the light emitting layer and the charge transporting layer may each independently be a single layer or a combination of a plurality of layers. Further, for example, a light emitting material other than the polymeric fluorescent substance described below may be mixed and used in the light emitting layer. Further, a layer in which the polymeric fluorescent substance and / or the charge transporting material is dispersed in a polymeric compound may be used.

As the charge transport material used with the polymeric fluorescent substance of the present invention, that is, as the electron transport material or the hole transport material, known materials can be used, and the hole transport material is not particularly limited, but a pyrazoline derivative is used. , Arylamine derivatives, stilbene derivatives, triphenyldiamine derivatives, etc., as electron transport materials, oxadiazole derivatives, anthraquinodimethane and its derivatives, benzoquinone and its derivatives, naphthoquinone and its derivatives, anthraquinone and its derivatives, tetracyano Examples thereof include anthraquinodimethane and its derivatives, fluorenone derivatives, diphenyldicyanoethylene and its derivatives, diphenoquinone derivatives, 8-hydroxyquinoline and its derivatives, and metal complexes.

Specifically, JP-A-63-70257,
JP-A-63-175860, JP-A-2-135359
And JP-A-2-135361, JP-A-2-209988, JP-A-3-37992, and JP-A-3-152184. Triphenyldiamine derivatives as hole transport materials, oxadiazole derivatives as electron transport materials, benzoquinone and its derivatives,
A metal complex of anthraquinone and its derivative, 8-hydroxyquinoline and its derivative is preferable, and in particular, 4,4′-bis (N (3-methylphenyl) -N-phenylamino) biphenyl, an electron transporting material as the hole transport material. The material is 2- (4-biphenylyl) -5- (4-t
-Butylphenyl) -1,3,4-oxadiazole,
Benzoquinone, anthraquinone and tris (8-quinolinol) aluminum are preferred. Among them, one or both of the electron transporting compound and the hole transporting compound may be used simultaneously. These may be used alone or as a mixture of two or more.

When a charge transport layer is further provided between the light emitting layer and the electrode, these charge transport materials may be used to form the charge transport layer. When the charge transporting material is used in a mixture with the light emitting layer, the amount of the charge transporting material varies depending on the kind of the compound to be used. It may be determined appropriately in consideration of the situation. Usually, it is 1 to 40% by weight, more preferably 2 to 30% by weight, based on the luminescent material.

Known light-emitting materials that can be used together with the polymeric fluorescent substance of the present invention are not particularly limited, and examples thereof include naphthalene derivatives, anthracene and its derivatives, perylene and its derivatives, polymethine series, xanthene series,
Coumarin-based, cyanine-based dyes, metal complexes of 8-hydroxyquinoline and its derivatives, aromatic amines,
Tetraphenylcyclopentadiene and its derivatives,
Tetraphenyl butadiene and its derivatives can be used. Specifically, for example, JP-A-57-51
Known materials such as those described in Japanese Patent Nos. 781 and 59-194393 can be used.

Next, an organic EL using the light emitting material of the present invention
A typical method for manufacturing a device will be described. A pair of electrodes consisting of an anode and a cathode, as a transparent or translucent electrode, on a transparent substrate such as glass or transparent plastic,
A transparent or semi-transparent electrode is used.
As the material of the anode, a conductive metal oxide film, a translucent metal thin film, or the like is used. Specifically, a film (NESA or the like) formed by using conductive glass made of indium tin oxide (ITO), tin oxide, or the like, gold, platinum, silver, copper, or the like is used. As a manufacturing method, a vacuum evaporation method, a sputtering method, a plating method, or the like is used.

On the anode, a light emitting layer containing the above polymeric fluorescent substance or the polymeric fluorescent substance and a charge transport material as a light emitting material is formed. Examples of the forming method include a coating method such as a spin coating method, a casting method, a dipping method, a bar coating method and a roll coating method using a melt, a solution or a mixed solution of these materials. It is particularly preferable to form the film by a coating method such as a spin coating method, a casting method, a dipping method, a bar coating method or a roll coating method.

The thickness of the light emitting layer is preferably 1 nm to
It is 1 μm, more preferably 2 nm to 500 nm.
5 to 200 to increase the current density and luminous efficiency
The range of nm is preferred. When the light emitting layer is formed into a thin film by a coating method, the solvent is removed. Therefore, after forming the light emitting layer, it is preferably under reduced pressure or in an inert atmosphere, preferably 30 to 3.
It is desirable to heat and dry at a temperature of 00 ° C, more preferably 60 to 200 ° C.

When a hole transport layer is laminated under the light emitting layer, it is preferable to form the hole transport layer before providing the light emitting layer by the above film forming method. The method for forming the hole transport layer is not particularly limited, but a vacuum deposition method from a powder state, or a spin coating method after dissolving in a solution,
Coating method such as casting method, dipping method, bar coating method, roll coating method, or spin coating method after mixing and dispersing a polymer compound and a charge transport material in a solution state or a molten state, casting method, dipping method A coating method such as a bar coating method and a roll coating method can be used. The polymer compound to be mixed is not particularly limited, but a compound that does not extremely disturb charge transport is preferable, and a compound that does not strongly absorb visible light is preferably used.

For example, poly (N-vinylcarbazole), polyaniline and its derivatives, polythiophene and its derivatives, poly (p-phenylene vinylene) and its derivatives, poly (2,5-thienylene vinylene).
And its derivatives, polycarbonate, polyacrylate, polymethyl acrylate, polymethyl methacrylate, polystyrene, polyvinyl chloride, polysiloxane and the like. In terms of easy film formation,
When a polymer compound is used, it is preferable to use a coating method.

The thickness of the hole transport layer is required to be at least such that pinholes are not generated, but if it is too thick, the resistance of the device increases and a high driving voltage is required, which is not preferable. Therefore, the thickness of the charge transport layer is preferably 1 nm to 1 μm, more preferably 2 nm to 500 n.
m, particularly preferably 5 to 200 nm.

When an electron transport layer is further laminated on the light emitting layer, it is preferable to form the electron transport layer on the light emitting layer after the light emitting layer is formed by the above-mentioned film forming method.

The method for forming the electron transport layer is not particularly limited, but it is a vacuum deposition method from a powder state, or a spin coating method after casting in a solution, a casting method, a dipping method, a bar coating method, a roll coating method. Or a coating method such as a spin coating method, a casting method, a dipping method, a bar coating method, or a roll coating method after a polymer compound and a charge transport material are mixed and dispersed in a solution state or a molten state. Can be used. The polymer compound to be mixed is not particularly limited, but a compound that does not extremely disturb charge transport is preferable, and a compound that does not strongly absorb visible light is preferably used.

For example, poly (N-vinylcarbazole), polyaniline and its derivatives, polythiophene and its derivatives, poly (p-phenylene vinylene) and its derivatives, poly (2,5-thienylene vinylene).
And its derivatives, polycarbonate, polyacrylate, polymethyl acrylate, polymethyl methacrylate, polystyrene, polyvinyl chloride, polysiloxane and the like. In terms of easy film formation,
When a polymer compound is used, it is preferable to use a coating method.

The film thickness of the electron transport layer needs to be at least such that pinholes are not generated, but if it is too thick, the resistance of the device increases and a high driving voltage is required, which is not preferable. Therefore, the thickness of the charge transport layer is preferably 1 nm to 1 μm, more preferably 2 nm to 500 n.
m, particularly preferably 5 to 200 nm.

Next, an electrode is provided on the light emitting layer or the electron transport layer. A cathode in which a first metal layer and a second metal layer made of a metal having a work function of 3.7 eV or less are stacked in contact with the first metal layer, or a cathode in which the first and second metal layers are stacked. And a third metal layer laminated on the cathode. This electrode serves as an electron injection cathode and is made of a metal having a work function of 3.7 eV or less or an alloy containing the metal. The first metal layer is, for example, gold, aluminum, silver, nickel, titanium,
Cobalt or the like is used. For the second metal layer, for example, a lithium aluminum alloy, a lithium silver alloy, a lithium indium alloy, a potassium aluminum alloy, a potassium silver alloy, a potassium indium alloy, or the like is used. For the third metal layer, for example, indium, aluminum or the like is used. As a method for manufacturing the cathode, a vacuum evaporation method, a sputtering method, or the like is used. In addition, after producing the cathode, the organic E
A protective layer for protecting the L element may be attached.

[0045]

EXAMPLES Examples of the present invention will be shown below, but the present invention is not limited to these examples. 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. Example 1 <Synthesis of polymeric fluorescent substance 1> 2,5-dioctyloxy-
p-Xylylene dibromide was reacted with triphenylphosphine in N, N-dimethylformamide solvent to synthesize a phosphonium salt. 47. The obtained phosphonium salt
75 parts by weight and 6.7 parts by weight of terephthalaldehyde were dissolved in ethyl alcohol. An ethyl alcohol solution containing 5.8 parts by weight of lithium ethoxide was added dropwise to an ethyl alcohol solution of a phosphonium salt and dialdehyde, and polymerized at room temperature for 3 hours. After leaving overnight at room temperature,
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 charging ratio of the monomers and the molar ratio thereof are shown below.

Embedded image 50: 50 (Two repeating units are alternately bonded.) The polystyrene-reduced number average molecular weight of the polymeric fluorescent substance 1 was 1.0 × 10 ⁴ . The structure of the polymeric fluorescent substance 1 was confirmed by infrared absorption spectrum and NMR.

<Production and Evaluation of Device> A glass substrate having an ITO film with a thickness of 40 nm was formed by sputtering using a 1.0 wt% chloroform solution of polyvinylcarbazole to form a film with a thickness of 50 nm. Furthermore, 1.0 wt% of the polymeric fluorescent substance 1
A film was formed to a thickness of 50 nm by spin coating using a toluene solution. Further, this was dried under reduced pressure at 150 ° C. for 1 hour, and then tris (8-quinolinol) aluminum (Alq ₃ ) was used as an electron transport layer in an amount of 0.1 to 0.2 n.
35 nm was deposited at a rate of m / s. The first of the cathode on it
After depositing aluminum to a thickness of 5 nm as the metal layer of the above, a lithium-aluminum alloy (lithium concentration: 1 wt%: manufactured by Honjo Metal Co., Ltd.) having a thickness of 40 nm was deposited as the second metal layer, and then having a thickness of 40 nm depositing aluminum as a third metal layer. An organic EL device was produced. The degree of vacuum at the time of vapor deposition was 8 × 10 ⁻⁶ Torr or less. Voltage 1 to this element
Applying 2.5V, current density 75.6mA / c
A current of m ² flowed, and yellowish green EL light emission with a luminance of 3136 cd / m ² was observed. The luminous efficiency at this time is 4.15.
cd / A (1.04 lm / W), and almost no non-light emitting portion (dark spot) was generated. The brightness was almost proportional to the current density. The EL peak wavelength is 54
At 0 nm, the fluorescence peak wavelength of the thin film of the polymeric fluorescent substance 1 was almost the same, and EL emission from the polymeric fluorescent substance 1 was confirmed.

Comparative Example 1 Same as Example 1 except that the first metal layer of the cathode was not used.
A device was prepared by the method. Apply a voltage of 12.5V to this device
When added, current density 0.163 mA / cm ^TwoCurrent
Flow, brightness of 4 cd / m^TwoYellowish green EL emission is observed
Was. The luminous efficiency at this time is 2.45 cd / A (0.
62 lm / W), and a dark spot was observed.
The brightness was almost proportional to the current density. Also, EL peak
The wavelength is 540 nm, and the fluorescence peak of the thin film of polymeric fluorescent substance 1 is
Emission from polymeric fluorescent substance 1 is almost the same as the wavelength
The light was confirmed.

As described above, in Example 1, aluminum was used as the first metal layer and lithium was used as the second metal layer.
An organic EL element using an aluminum alloy and further using aluminum as a third metal layer has a lower workability than the organic EL element of Comparative Example 1 in which a metal having a small work function is directly deposited on the organic layer without the first metal layer. High luminous efficiency, long life,
It showed excellent EL characteristics, such as few dark spots.

[0050]

The organic electroluminescence device of the present invention has a cathode formed by laminating metals, so that it is easy to prepare, and has high brightness, high luminous efficiency, long life and low driving voltage. Further, the third metal layer acts as a protective layer, and the durability of the cathode is high, so that the life can be extended and the generation of dark spots can be suppressed. Therefore, the organic electroluminescent device of the present invention can be preferably used as a device such as a planar light source as a backlight and a flat panel display.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the layer structure of an organic electroluminescence device having a two-layer structure cathode of the present invention.

FIG. 2 is a cross-sectional view showing the layer structure of an organic electroluminescence device having a three-layer structure cathode of the present invention.

[Explanation of symbols]

 1 ... Glass plate. 2 Anode (transparent electrode). 3 ... Hole transport layer. 4 ... Light emitting layer. 5 ... Electron transport layer. 6 ... the first metal layer of the cathode. 7 ... Second metal layer of cathode. 8 ... Third metal layer of cathode.

Front page continuation (72) Inventor Yoshihiko Tsuchida 6 Kitahara, Tsukuba, Ibaraki Sumitomo Chemical Co., Ltd.

Claims (6)

[Claims] 1. In an organic electroluminescent device having at least a light emitting layer between a pair of electrodes, at least one of which is transparent or semitransparent, comprising an anode and a cathode, the cathode in contact with the light emitting layer is composed of two or more metal layers. ,
The two metal layers are laminated in order of a light emitting layer, a first metal layer, and a second metal layer, and the first metal layer in contact with the light emitting layer is made of a metal having a work function of more than 3.7 eV. And a thickness of 20 nm or less, and the second metal layer is made of a metal having a work function of 3.7 eV or less. 2. In an organic electroluminescence device having at least a light emitting layer between an electrode composed of a pair of an anode and a cathode, at least one of which is transparent or semitransparent, the cathode in contact with the light emitting layer is composed of three or more metal layers. ,
The three metal layers are laminated in order of a light emitting layer, a first metal layer, a second metal layer, and a third metal layer, and the first metal layer in contact with the light emitting layer has a work function of 3 A metal of more than 0.7 eV and a thickness of 20 nm or less, the second metal layer of a metal having a work function of 3.7 eV or less, and the third metal layer of platinum, silver, gold or nickel. An organic electroluminescence device comprising a metal selected from titanium, tantalum, indium, and aluminum. 3. The light emitting layer comprises a repeating unit having a conjugated structure as a main chain, and has a polystyrene reduced number average molecular weight of 10 ³ to.
The organic electroluminescence device according to claim 1 or 2, wherein the organic electroluminescence device comprises 10 ⁷ and contains a polymer having fluorescence in a solid state. 4. The organic electroluminescence device according to claim 1, wherein a layer made of an electron transporting compound is provided between the cathode and the light emitting layer adjacent to the light emitting layer. 5. The organic electroluminescence device according to claim 1, wherein a layer made of a hole transporting compound is provided between the anode and the light emitting layer adjacent to the light emitting layer. 6. A layer made of an electron transporting compound is provided between the cathode and the light emitting layer adjacent to the light emitting layer, and a hole is provided adjacent to the light emitting layer between the anode and the light emitting layer. The organic electroluminescence device according to claim 1, further comprising a layer made of a transporting compound.