JP2008031496A - Transparent electrode for organic electroluminescence - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transparent electrode for an organic EL having a smooth surface and excellent acid resistance and unnecessary for any polishing process, and to provide an organic electroluminescence element which has an anode buffer layer formed by a wet method (a coating method) from an acidic organic polymer material by using the transparent electrode as an anode. <P>SOLUTION: In a transparent conductive film other than crystalline ITO, the oxidation-reduction potential is ≥(E-0.1)V and ≤(E+1.0)V where the oxidation-reduction potential of the crystalline ITO is E(V) in a polar solvent at 25°C in which a supporting electrolyte is dissolved. An organic EL element uses the transparent conductive film as an anode. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an organic electroluminescence (hereinafter abbreviated as organic EL) element and a method for producing the same.

As the development of the information and communication industry accelerates, display elements having high performance are required, and organic EL elements are attracting attention as next-generation display elements.
The organic EL element has an advantage of not only a wide viewing angle and excellent contrast as a spontaneous emission type display element but also a quick response time. In general, an organic EL element is composed of a light emitting layer and a pair of counter electrodes sandwiching the layer. In light emission, when an electric field is applied between both electrodes, electrons are injected from the cathode side and holes are injected from the anode side. Furthermore, this is a phenomenon in which electrons recombine with holes in the light emitting layer to generate an excited state, and energy is emitted as light when the excited state returns to the ground state.

  The organic EL element originates from the stacked type element reported by Tang et al. In 1987, and since then, the characteristics as the element have improved dramatically and has already been put into practical use in personal computer terminals, mobile phones and the like. .

Conventional examples already in practical use include ITO (indium and tin oxide transparent electrode) as the anode, CuPc (copper phthalocyanine) as the anode buffer layer, TPD (triphenyldiamine derivative) as the hole transport layer, and light emitting layer There is an organic EL element configured in this order using Alq3 (aluminum complex) serving as an electron transporting layer, LiF (lithium fluoride) as a cathode buffer layer, and Al (aluminum) as a cathode (for example, non-patent literature) 1).
However, in this practical application technique, since the organic thin film layer is formed by dry film formation such as a sputtering method, it is difficult to increase the size. Moreover, since ITO used as the anode is usually crystallized, there is a possibility that leakage of the organic EL element may be caused by unevenness of crystal grains.

On the other hand, by forming the organic thin film layer by wet film formation such as spin coating or ink jet, the manufacturing process of the organic EL element is simplified and the manufacturing process is becoming economical.
Poly (3,4-ethylenedioxythiophene) / polystyrene sulfonic acid having excellent hole injection properties when forming a hole injection / transport layer on a transparent electrode made of ITO by a wet method (coating method) A (PEDOT / PSS) colloidal dispersion aqueous solution is suitably used (for example, see Patent Document 1).

  When PEDOT / PSS with high acidity is used as the conductive polymer material and the hole injection / transport layer in contact with the anode is formed by a wet method (coating method), the material constituting the anode is dissolved by an acid. It is necessary to use materials that are not. For these reasons, conventionally, when the hole injection / transport layer is formed by a wet method (coating method), tin-doped indium oxide (ITO) that is not dissolved by an acid is used as the anode material.

However, as described above, ITO is an expensive material, and has high crystallinity and low surface smoothness. Therefore, in order to use it as an anode, a polishing step for smoothing the surface is required.
On the other hand, an oxide of indium and zinc (IZO) is known as an electrode material that does not require polishing (see Patent Document 2). Since IZO is amorphous, it has excellent surface smoothness when formed into a film, and at the same time has excellent adhesion to other materials, and is very useful as an electrode material for organic electroluminescence elements.
However, when IZO is used as the anode material and PEDOT / PSS, which is an acidic hole injection / transport material, is applied thereto, IZO is dissolved by the sulfonic acid in the PSS. It was not suitable for forming a hole injection / transport layer.

JP 2005-259532 A JP-A-10-308284 E. W. Forsythe, M .; A. Abkouitz, Y .; Gao, and C.I. W. Tang, “Influence of copper phthalocyanine on the charge injection and growth modes for organic light emitting diodes”, J. Am. Vac. Sci. Technol. A, vol. 18, no. 4, pp. 1869-1874, 2001

  In view of the above situation, the present invention has a smooth surface, does not require a polishing step, and at the same time has excellent acid resistance, and uses a transparent conductive film, a transparent electrode for organic EL, and this transparent electrode as an anode. An object of the present invention is to provide an organic electroluminescence device having an anode buffer layer formed from a molecular material by a wet method (coating method).

  In order to achieve the above object, the present inventor has conducted intensive research and has a transparent mixture of an oxide of a specific metal element added to an oxide of at least one metal element selected from indium, zinc or tin. It has been found that the electrode has excellent surface smoothness and acid resistance, and is useful as a transparent electrode for an organic EL device formed by applying an acidic organic polymer material to an organic layer in contact with the transparent electrode. The present invention has been completed.

That is, this invention provides the following transparent electrode, the transparent electrode for organic electroluminescent elements, a sputtering target, the organic electroluminescent element using the said transparent electrode, and its manufacturing method.
1. In a polar solvent at 25 ° C. in which the supporting electrolyte is dissolved, when the oxidation-reduction potential of crystalline ITO is E (V), the oxidation-reduction potential is (E−0.1) V or more, (E + 1.0) A transparent conductive film other than crystalline ITO in the range of V or less.
2. An oxide of at least one metal selected from indium, zinc and tin, and aluminum, titanium, vanadium, manganese, iron, cobalt, nickel, copper, gallium, germanium, strontium, niobium, molybdenum, palladium, silver, antimony 2. The transparent conductive film according to 1 above, comprising a mixture of an oxide of at least one element selected from tantalum, barium, hafnium, tantalum, tungsten, iridium, and a rare earth element.
3. (A) an oxide of at least one metal selected from indium, zinc, and tin; and (B) at least one selected from aluminum, titanium, molybdenum, tantalum, tungsten, cerium, samarium, gadolinium, and neodymium. 3. The transparent conductive film according to 2 above, comprising a mixture with an oxide of the element.
4). 4. The transparent conductive film according to 3 above, wherein the ratio (A) :( B) (weight ratio) of the metal oxide (A) to the metal oxide (B) is in the range of 50 to 90:10 to 50. .
5. The transparent electrode for organic electroluminescent elements which consists of a transparent conductive film in any one of said 1-4.
6). An oxide of at least one metal selected from indium, zinc and tin, and aluminum, titanium, vanadium, manganese, iron, cobalt, nickel, copper, gallium, germanium, strontium, niobium, molybdenum, palladium, silver, antimony A sputtering target comprising a mixture of oxides of at least one element selected from tantalum, barium, hafnium, tantalum, tungsten, iridium, and rare earth elements.
7). (A) an oxide of at least one metal selected from indium, zinc, and tin; and (B) at least one selected from aluminum, titanium, molybdenum, tantalum, tungsten, cerium, samarium, gadolinium, and neodymium. 7. The sputtering target according to 6 above, comprising a mixture with an oxide of the element.
8). 8. The sputtering target according to 7 above, wherein the ratio (A) :( B) (weight ratio) between the metal oxide (A) and the metal oxide (B) is in the range of 50 to 90:10 to 50.
9. 6. An organic electroluminescence device comprising a plurality of organic thin film layers including at least a light emitting layer sandwiched between a cathode and an anode, wherein the transparent electrode described in 5 above is used as an anode.
10. 10. The organic electroluminescence device according to 9, wherein the organic electroluminescence device has an anode buffer layer adjacent to the anode, and the anode buffer layer is made of an organic polymer material.
11. 11. The organic electroluminescence device according to 10 above, wherein the dopant anion of the organic polymer material is acidic in a polar solvent.
12 12. The organic electroluminescence device according to 10 or 11, wherein the organic polymer material is polyethylene dioxythiophene / polystyrene sulfonic acid (PEDOT / PSS) or polyaniline / camphor sulfonic acid (PANI / CSA).
13. 13. The organic electroluminescence device according to any one of 10 to 12, wherein the anode buffer layer has a thickness of 1 nm to 500 nm.
14 14. The method for producing an organic electroluminescent element according to any one of 10 to 13, wherein the anode buffer layer is formed by spin-coating an aqueous solution of an organic polymer material on the anode.

ADVANTAGE OF THE INVENTION According to this invention, the transparent conductive film excellent in surface smoothness and acid resistance, and the transparent electrode for organic EL elements consisting thereof can be provided.
ADVANTAGE OF THE INVENTION According to this invention, the sputtering target for forming the transparent conductive film excellent in surface smoothness and acid resistance, or the transparent electrode for organic EL elements consisting thereof can be provided.
The transparent conductive film and the transparent electrode for organic EL elements of the present invention are formed in contact with the transparent electrode because they have excellent surface smoothness and do not require a polishing step, and are excellent in acid resistance. The organic layer can be formed efficiently and economically by applying a highly acidic organic polymer material.

The present invention will be specifically described below.
1. Transparent conductive film, transparent electrode for organic EL element and sputtering target comprising the transparent conductive film of the present invention and transparent electrode for organic EL element comprising the same (hereinafter, both may be collectively referred to as “transparent electrode of the present invention”) In a 25 ° C. polar solvent in which the supporting electrolyte is dissolved, when the oxidation-reduction potential of crystalline ITO is E (V), the oxidation-reduction potential is (E−0.1) V or more, and (E + 1.0 ) V or less. However, other than crystalline ITO is excluded.

Here, the “supporting electrolyte” is a salt, and specifically includes lithium chloride, lithium perchlorate, quaternary alkylammonium borofluoride, etc., and those having high solubility are appropriately selected depending on the solvent used. . By adding the supporting electrolyte to the solvent, the solution resistance can be eliminated, and the supporting electrolyte is added in order to correctly measure the redox potential. And the solvent which can melt | dissolve a supporting electrolyte is a polar solvent, Specifically, nonaqueous polar solvents, such as alcohol, acetonitrile, propylene carbonate, nitromethane other than water, are mentioned.
Although the redox potential of crystalline ITO varies depending on the type of polar solvent to be used, since the redox potential of the transparent electrode of the present invention is measured under the same conditions, (E-0.1) V or more, ( The range of E + 1.0) V or less only shifts with the fluctuation of the redox potential of crystalline ITO.

Here, crystalline ITO refers to one in which a crystal structure (Bixbite structure) of indium oxide is recognized when X-ray diffraction is measured. In addition, since the oxidation-reduction potential of crystalline ITO changes with film forming conditions, the film forming method and film forming conditions of crystalline ITO in the present invention are as follows.
Film formation method: Magnetron sputtering method using oxide target Substrate: Alkali-free glass Ultimate vacuum: 5 × 10 ⁻⁴ Pa
Sputtering gas: Ar 98%, O ₂ 2%
Sputtering pressure: 0.1 Pa
Substrate temperature: 250 ° C
Sputter output: 1 W / cm ²
Sputtering time: 10 minutes

  If the redox potential of the transparent electrode of the present invention is less than (E-0.1) V, it may be dissolved when a hole injection material that shows acidity when applied to an aqueous solution such as PEDOT-PSS is applied. If it exceeds (E + 1.0) V, it means that the material has a very low carrier concentration, so that it may not function as an electrode. The redox potential of the transparent electrode of the present invention is preferably (E-0.05) V or more and (E + 0.8) V or less, (E-0.03) V or more, (E + 0.5) V. The following is more preferable.

Specifically, the redox potential of the crystalline ITO and the transparent electrode of the present invention can be measured by the following conditions and methods.
<Devices used and measurement conditions>
Potentiostat: Hokuto Denko HA-151
Electrolyte: 3 mol / L KCl aqueous solution (25 ° C.)
Working electrode: crystalline ITO electrode or transparent electrode of the present invention Reference electrode: SCE (saturated calomel electrode)
Counter electrode: Platinum <Measurement method>
The three electrodes are immersed in the electrolytic solution, electrically connected to the potentiostat, and the potential of the working electrode with respect to the reference electrode is read from the potentiostat display.

  More specifically, for example, the redox potential E of crystalline ITO in 25 ° C. water (polar solvent) in which 3 mol / L of calcium chloride is dissolved as a supporting electrolyte is 0.32V. Therefore, the range of the oxidation-reduction potential of the transparent electrode of the present invention is specified as 0.22 V or more ((E−0.1) V or more) and 1.32 V or less ((E + 0.1) V or less).

  The transparent electrode of the present invention comprises an oxide of at least one metal selected from indium, zinc, and tin, and aluminum, titanium, vanadium, manganese, iron, cobalt, nickel, copper, gallium, germanium, strontium, niobium, It is preferable that it is composed of a mixture of molybdenum, palladium, silver, antimony, barium, hafnium, tantalum, tungsten, iridium, and an oxide of at least one element selected from rare earth elements. , Having an oxidation-reduction potential in the above range.

Here, the former metal oxide group and the latter metal oxide group are considered to perform the following functions, respectively.
That is, the metal oxide contained in the former metal oxide group serves as a base material of the transparent electrode material, and by adding the metal oxide contained in the latter metal oxide group to the base material, The redox potential of can be adjusted in the noble direction.

Since the transparent electrode of the present invention has the above elemental composition, it has an oxidation-reduction potential in the above range. By containing two kinds of metals, the balance of the following two mechanisms can be adjusted. Because. That is,
1. If it is a noble metal oxide, the oxidation-reduction potential is larger, and if it is a base metal oxide, the oxidation-reduction potential is smaller.
2. The higher the carrier concentration of the electrode, the lower the redox potential, and the lower the carrier concentration, the higher the redox potential.

  The transparent electrode of the present invention comprises (A) an oxide of at least one metal selected from indium, zinc, and tin; and (B) aluminum, titanium, molybdenum, tantalum, tungsten, cerium, samarium, gadolinium, and neodymium. It is preferable to consist of a mixture with an oxide of at least one element selected from

  Furthermore, in the transparent electrode of the present invention, the ratio (A) :( B) (weight ratio) of the metal oxide (A) and the metal oxide (B) is within the range of 50 to 90:10 to 50. Preferably there is. If the ratio (weight ratio) of the metal oxide (B) is less than 10, the oxidation-reduction potential value may be lower than E-0.1V, and if it exceeds 50, the carrier concentration is greatly reduced, May stop functioning. As for the ratio (weight ratio) of a metal oxide (A) and a metal oxide (B), it is more preferable to exist in the range of 70-90: 10-30.

The transparent electrode of the present invention can be produced by sputtering using the sputtering target of the present invention described later.
The sputtering target of the present invention includes an oxide of at least one metal selected from indium, zinc and tin, and aluminum, titanium, vanadium, manganese, iron, cobalt, nickel, copper, gallium, germanium, strontium, niobium, It is characterized by comprising a mixture of molybdenum, palladium, silver, antimony, barium, hafnium, tantalum, tungsten, iridium, and an oxide of at least one element selected from rare earth elements. By comprising in this way, the transparent electrode of this invention which has the oxidation-reduction potential of a desired range can be obtained.

  The sputtering target of the present invention includes (A) an oxide of at least one metal selected from indium, zinc, and tin, and (B) aluminum, titanium, molybdenum, tantalum, tungsten, cerium, samarium, gadolinium, and neodymium. It is preferable that it consists of a mixture with an oxide of at least one element selected from the following: and the ratio (A) :( B) (weight ratio) of the metal oxide (A) and the metal oxide (B) ) Is preferably in the range of 50 to 90:10 to 50. The reason for this is as described for the transparent electrode of the present invention.

  The sputtering target of the present invention can be manufactured as follows. The predetermined metal oxide powder having a desired metal oxide composition is mixed so as to have a predetermined molar ratio, accommodated in a wet ball mill container, and mixed and ground for 1 to 100 hours. Next, the obtained pulverized product was granulated and then press-molded to a size of 2 to 10 inches in diameter and 2 to 5 mm in thickness. After storing this in a firing furnace, the sputtering target of the present invention is obtained by heating and firing at a temperature of 1200 to 1500 ° C. for 1 to 48 hours.

The production of the transparent electrode of the present invention is specifically performed by placing the transparent glass substrate and the sputtering target of the present invention in a vacuum chamber shared by the high-frequency sputtering apparatus and the vacuum evaporation apparatus, and operating the high-frequency sputtering apparatus. Then, a transparent electrode film (transparent conductive film of the present invention) having a thickness of 10 to 200 nm is formed. Incidentally, while pressure of the vacuum degree to ¹⁰ -5 ^{to 10} -3 Pa, a gas obtained by mixing oxygen gas into argon gas was filled, during the atmosphere, the ultimate vacuum 0.01～1Pa, the substrate temperature from room temperature to Sputtering is performed under the conditions of 150 ° C., input power of 0.5 to 3 W / cm ² , and film formation time of 1 to 10 minutes.

  Since the surface of the transparent electrode of the present invention obtained as described above is excellent in smoothness, it does not require a polishing step and has excellent adhesion to other layers.

Since the transparent conductive film of the present invention is excellent in surface smoothness and acid resistance, it is useful as a transparent electrode constituting the anode of an organic EL device.
In addition, the transparent electrode of the present invention is excellent in acid resistance as shown in the Examples, and in particular, the layer adjacent to the transparent electrode (anode) for the organic EL element of the present invention is made of a highly acidic conductive polymer. Even when the electrode is formed from a material by a wet method (coating method), the electrode is not dissolved by an acid, and therefore dark spots are hardly generated.

2. Organic EL element An organic EL element is characterized in that in the organic electroluminescence element in which a plurality of organic thin film layers including at least a light emitting layer are sandwiched between a cathode and an anode, the transparent electrode of the present invention is used as an anode. To do. The advantages of using the transparent electrode of the present invention as an anode are as described above.
The layer structure of the organic EL element of the present invention may be any structure except that the transparent electrode of the present invention is used as an anode. For example, the anode buffer layer to be described later may not be made of an organic polymer material, and a hole injection layer, a hole transport layer, an electron injection layer, an electron transport layer, the presence or absence of other organic thin film layers, There are no particular limitations on the constituent materials and the method for forming each layer (either a dry method or a wet method).

  The organic EL device of the present invention preferably has an anode buffer layer adjacent to the anode, and the anode buffer layer is preferably made of an organic polymer material. Here, the “anode buffer layer” is a layer for efficiently injecting holes from the electrode into the hole transport layer or the light emitting layer, and is usually a hole injection layer or a hole transport layer.

As an organic polymer material (hole injection / transport material) that constitutes the anode buffer layer, it has the ability to transport holes, has a positive hole injection effect from the anode, and is superior to the light emitting layer or light emitting material. A compound that has an injection effect, prevents exciton generated in the light emitting layer from moving to the electron injection layer, and has excellent thin film forming ability is preferable.
Specifically, phthalocyanine derivatives, naphthalocyanine derivatives, porphyrin derivatives, oxazole, oxadiazole, triazole, imidazole, imidazolone, imidazolethione, pyrazoline, pyrazolone, tetrahydroimidazole, oxazole, oxadiazole, hydrazone, acyl hydrazone, polyaryl Alkane, stilbene, butadiene, benzidine type triphenylamine, styrylamine type triphenylamine, diamine type triphenylamine, and their derivatives, polyvinylcarbazole, polymers such as polysilane, polyethylenedioxythiophene / polystyrene sulfonic acid (PEDOT / PSS), polymer materials such as polyaniline / camphorsulfonic acid (PANI / CSA) and other conductive polymers And the like.

Specific examples of the aromatic tertiary amine derivative include triphenylamine, tolylamine, tolyldiphenylamine, N, N′-diphenyl-N, N ′-(3-methylphenyl) -1,1′-biphenyl-4 , 4′-diamine, N, N, N ′, N ′-(4-methylphenyl) -1,1′-phenyl-4,4′-diamine, N, N, N ′, N ′-(4- Methylphenyl) -1,1′-biphenyl-4,4′-diamine, N, N′-diphenyl-N, N′-dinaphthyl-1,1′-biphenyl-4,4′-diamine, N, N ′ -(Methylphenyl) -N, N '-(4-n-butylphenyl) -phenanthrene-9,10-diamine, N, N-bis (4-di-4-tolylaminophenyl) -4-phenyl-cyclohexane Etc., or having these aromatic tertiary amine skeletons It is a oligomer or polymer, but is not limited thereto.

Specific examples of the phthalocyanine (Pc) derivative include H ₂ Pc, CuPc, CoPc, NiPc, ZnPc, PdPc, FePc, MnPc, ClAlPc, ClGaPc, ClInPc, ClSnPc, Cl ₂ SiPc, (HO) AlPc, (HO) Although it is a phthalocyanine derivative and a naphthalocyanine derivative such as GaPc, VOPc, TiOPc, MoOPc, and GaPc-O-GaPc, it is not limited thereto.

In this invention, since the transparent electrode which comprises an anode is excellent in acid resistance, even if the dopant anion of the organic polymer material which comprises an anode buffer layer is acidic in a polar solvent, it can use preferably. Here, examples of the polar solvent include non-aqueous polar solvents such as water, alcohols, acetonitrile, propylene carbonate, and nitromethane.
Examples of the organic polymer material in which such a dopant anion is acidic in a polar solvent include polyethylene dioxythiophene / polystyrene sulfonic acid (PEDOT / PSS), polyaniline / camphor sulfonic acid (PANI / CSA), and the like. .

The structural formulas of PEDOT / PSS and PANI / CAS are shown below.

In the present invention, the anode buffer layer is prepared by dissolving an organic polymer material in a solution as an ink, and methods such as spin coating, bar coating, and ink jet are used. In addition, a monomer such as aniline or thiophene can be dissolved in a solvent together with the supporting electrolyte, and electrolytically oxidized using a transparent electrode such as ITO or IZO as an anode, whereby a conductive polymer can be formed and used as a buffer layer. The supporting electrolyte may be any material that is sufficiently soluble in a polar solvent, such as LiBF ₄ , LiClO ₄ , TBABF ₄ (tetrabutylammonium tetrafluoroborate).

  The film thickness of the anode buffer layer is usually 1 to 500 nm, preferably 1 to 100 nm, more preferably 5 to 20 nm. If the thickness of the anode buffer layer is less than 1 nm, it is difficult to form a uniform film, and the function as a buffer layer may be lost. If the thickness exceeds 500 nm, the buffer layer itself may be deteriorated.

3. Manufacturing method of organic EL element The manufacturing method of the organic EL element of the present invention is characterized in that an anode buffer layer is formed by spin-coating an aqueous solution of the organic polymer material on the anode which is the transparent electrode of the present invention. And In the manufacturing method of the organic EL element of the present invention, any layer configuration may be used except that the transparent electrode of the present invention is used as an anode and the above-described method for forming an anode buffer layer is used. The formation method is not limited.

A schematic diagram showing one embodiment of the layer structure of the organic EL device of the present invention is shown in FIG. The organic EL device of the present invention has an organic thin film layer including a light emitting layer 14 between at least the anode 10 and the cathode 18. In the present invention, the anode buffer layer 12 is typically adjacent to the anode.
Since the anode 10 is as described above, it is omitted here, and the other organic thin film layer, other layers, and the like including the light emitting layer 14, the cathode 18, and the anode buffer layer 12 as necessary are described below. .

(1) Constituent material of light emitting layer Organic light emitting layer The organic light emitting material used as a constituent material of the organic light emitting layer 14 preferably has the following three functions.
(A) Charge injection function: A function capable of injecting holes from the anode or the hole injection layer and applying electrons from the cathode layer or the electron injection layer when an electric field is applied.
(B) Transport function: a function of moving injected holes and electrons by the force of an electric field.
(C) Light emitting function: A function that provides a field for recombination of electrons and holes and connects them to light emission.

  However, it is not always necessary to have all the functions (a) to (c). For example, the organic light-emitting material has a hole injection / transport property larger than an electron injection / transport property. There is a suitable one. Therefore, any material can be preferably used as long as the movement of electrons in the organic light emitting layer 14 is promoted and holes and electrons can be recombined near the center inside the organic light emitting layer 14.

Here, in order to improve the recombination property in the organic light emitting layer 14, the electron mobility of the organic light emitting material is preferably set to a value of 1 × 10 ⁻⁷ cm ² / V · s or more. This is because when the value is less than 1 × 10 ⁻⁷ cm ² / V · s, high-speed response in the organic EL element may be difficult, or the light emission luminance may decrease. Therefore, the electron mobility of the organic light emitting material is more preferably set to a value within the range of 1.1 × 10 ⁻⁷ to 2 × 10 ⁻³ cm ² / V · s, and 1.2 × 10 ⁻⁷ to More preferably, the value is in the range of 1.0 × 10 ⁻³ cm ² / V · s.

  Moreover, it is preferable to make the value of electron mobility smaller than the hole mobility of the organic light emitting material in the organic light emitting layer 14. When this relationship is reversed, the organic light emitting material that can be used for the organic light emitting layer 14 may be excessively limited, and the light emission luminance may be reduced. On the other hand, it is preferable that the electron mobility of the organic light emitting material is larger than 1/1000 of the value of hole mobility. This is because if the electron mobility becomes excessively small, it becomes difficult for holes and electrons to recombine in the vicinity of the center inside the organic light emitting layer 14, and the light emission luminance may decrease. Therefore, it is more preferable that the hole mobility (μh) and the electron mobility (μe) of the organic light emitting material in the organic light emitting layer 14 satisfy the relationship of μh / 2> μe> μh / 500, and μh / 3 It is more preferable that the relationship of> μe> μh / 100 is satisfied.

  Examples of the light emitting material used for the light emitting layer include olefin-based light emitting materials such as 4,4 ′-(2,2-diphenylvinyl) biphenyl, 9,10-di (2-naphthyl) anthracene, 9,10-bis (3, 5-diphenylphenyl) anthracene, 9,10-bis (9,9-dimethylfluorenyl) anthracene, 9,10- (4- (2,2-diphenylvinyl) phenyl) anthracene, 9,10′-bis ( 2-biphenylyl) -9,9′-bisanthracene, 9,10,9 ′, 10′-tetraphenyl-2,2′-bianthryl, 1,4-bis (9-phenyl-10-anthracenyl) benzene, etc. Anthracene-based luminescent materials, spiro-based luminescent materials such as 2,7,2 ′, 7′-tetrakis (2,2-diphenylvinyl) spirobifluorene, 4,4′-dicarba Carbazole-based luminescent materials such as rilbiphenyl and 1,3-dicarbazolylbenzene, low-molecular luminescent materials typified by pyrene-based luminescent materials such as 1,3,5-tripyrenylbenzene, polyphenylene vinylenes, polyfluorene And polymer light-emitting materials typified by polyvinyl carbazoles. Among these, a low molecular weight light emitting material is preferable as the light emitting material, and an anthracene light emitting material is more preferable.

  The light emitting layer may be doped with a fluorescent dye. The concentration of doping is not particularly limited, but is preferably 0.1 to 20% by weight. Specific examples of fluorescent dyes include known fluorescent dyes such as perylene derivatives, pyrene derivatives, chrysene derivatives, phenanthrene derivatives, rubrene derivatives, coumarin derivatives, dicyanomethylenepyran derivatives, stilbene derivatives, tristyrylarylene derivatives, and distyrylarylene derivatives. be able to. Of these, preferred fluorescent dyes are perylene derivatives, pyrene derivatives, and distyrylarylene derivatives, and more preferred are arylamino-substituted distyrylarylene derivatives and arylamino-substituted pyrene derivatives.

  The light emitting layer may be doped with a phosphorescent dye. The concentration of doping is not particularly limited, but is preferably 0.1 to 20% by weight. Specific examples of phosphorescent dyes include platinum complexes such as tetraphenylporphyrin platinum complex, tris (2-phenylpyridine) iridium, bis (2-phenylpyridine) (acetylacetonato) iridium, bis (2,4-difluorophenyl). Examples thereof include iridium complexes represented by pyridine) (picolinato) iridium, bis (2-phenylquinoline) (acetylacetonato) iridium, bis (2-phenylbenzothiazole) (acetylacetonato) iridium, and the like. Of these, the preferred phosphorescent dye is an iridium complex, and more preferably an orthometalated iridium complex.

Next, a method for forming the organic light emitting layer 14 will be described. Such a forming method is not limited to a specific method. For example, methods such as a vacuum deposition method, a spin coating method, a casting method, an LB method, and a sputtering method can be employed. For example, in the case of forming by a vacuum deposition method, the deposition temperature is 50 to 450 ° C., the degree of vacuum is 1 × 10 ⁻⁷ to 1 × 10 ⁻³ Pa, the film formation rate is 0.01 to 50 nm / second, and the substrate temperature is −50 to 300. It is preferable to adopt the condition of ° C.

  Alternatively, the organic light emitting layer 14 can also be formed by dissolving the binder and the organic light emitting material in a predetermined solvent to form a solution and then reducing the film thickness by spin coating or the like. The organic light emitting layer 14 is formed by selecting a forming method and forming conditions as appropriate and solidifying from a thin film formed by deposition from a material compound in a gas phase state or a material compound in a solution state or a liquid phase state. It is preferable to use a molecular deposition film which is a thick film. Usually, this molecular deposited film can be sufficiently distinguished from a thin film (molecular accumulated film) formed by the LB method by the difference in aggregated structure and higher order structure and the functional difference resulting therefrom.

The film thickness of the organic light-emitting layer is not particularly limited, and an appropriate film thickness can be selected according to the situation, but in reality, a value in the range of 5 nm to 5 μm is preferable. There are many cases. The reason for this is that when the thickness of the organic light emitting layer is less than 5 nm, the light emission luminance and durability may decrease. On the other hand, when the thickness of the organic light emitting layer 14 exceeds 5 μm, the value of the applied voltage increases. This is because there are many cases. Therefore, since the balance with the value of light emission luminance, applied voltage, etc. becomes better, the thickness of the organic light emitting layer 14 is more preferably set to a value within the range of 10 nm to 3 μm, and within the range of 20 nm to 1 μm. More preferably, the value of

(2) Constituent material of cathode cathode layer It is preferable to use a metal, an alloy, an electrically conductive compound, or a mixture thereof having a small work function (for example, less than 4.0 eV) for the cathode layer 18. Specifically, one of magnesium, aluminum, indium, lithium, sodium, cesium, silver and the like can be used alone or in combination of two or more, but the invention is not limited to these. Examples of alloys include magnesium / silver, magnesium / indium, lithium / aluminum, and the like, but are not limited thereto. The ratio of the alloy is controlled by the temperature of the vapor deposition source, the atmosphere, the degree of vacuum, etc., and is selected to an appropriate ratio. If necessary, the cathode may be formed of two or more layers.

The thickness of the cathode layer The thickness of the cathode layer 18 is not particularly limited, but is preferably a value in the range of 10 to 1000 nm, and more preferably in the range of 10 to 200 nm.

(3) Other organic thin film layers (i) Hole injection / transport layer The hole injection / transport layer and the anode buffer layer are the same as described above, and are omitted here.

(Ii) Electron injection / transport layer The electron injection / transport layer means an electron injection layer and / or an electron transport layer, and as an electron injection / transport material, it has the ability to transport electrons and has an electron injection effect from a cathode. A compound that has an excellent electron injection effect for the light emitting layer or the light emitting material, prevents migration of excitons generated in the light emitting layer to the hole injection layer, and has an excellent thin film forming ability is preferable. Specifically, fluorenone, anthraquinodimethane, diphenoquinone, thiopyran dioxide, oxazole, oxadiazole, triazole, imidazole, perylenetetracarboxylic acid, fluorenylidenemethane, anthraquinodimethane, anthrone, etc. and their derivatives However, it is not limited to these. Further, the charge injection property can be improved by adding an electron accepting material to the hole injecting material and an electron donating material to the electron injecting material.

Among the electron injecting / transporting materials, more effective materials are metal complex compounds or nitrogen-containing five-membered ring derivatives.
Specific examples of the metal complex compound include 8-hydroxyquinolinate lithium, bis (8-hydroxyquinolinato) zinc, bis (8-hydroxyquinolinato) copper, bis (8-hydroxyquinolinato) manganese, Tris (8-hydroxyquinolinato) aluminum, tris (2-methyl-8-hydroxyquinolinato) aluminum, tris (8-hydroxyquinolinato) gallium, bis (10-hydroxybenzo [h] quinolinato) beryllium, Bis (10-hydroxybenzo [h] quinolinato) zinc, bis (2-methyl-8-quinolinato) chlorogallium, bis (2-methyl-8-quinolinato) (o-cresolate) gallium, bis (2-methyl-8) -Quinolinato) (1-naphtholato) aluminum, bis (2-methyl) Le-8-quinolinate) (2-naphtholato) Gallium like, but it is not limited thereto.

  The nitrogen-containing five-membered derivative is preferably an oxazole, thiazole, oxadiazole, thiadiazole or triazole derivative. Specifically, 2,5-bis (1-phenyl) -1,3,4-oxazole, dimethyl POPOP, 2,5-bis (1-phenyl) -1,3,4-thiazole, 2,5- Bis (1-phenyl) -1,3,4-oxadiazole, 2- (4′-tert-butylphenyl) -5- (4 ″ -biphenyl) 1,3,4-oxadiazole, 2,5 -Bis (1-naphthyl) -1,3,4-oxadiazole, 1,4-bis [2- (5-phenyloxadiazolyl)] benzene, 1,4-bis [2- (5-phenyloxa) Diazolyl) -4-tert-butylbenzene], 2- (4′-tert-butylphenyl) -5- (4 ″ -biphenyl) -1,3,4-thiadiazole, 2,5-bis (1-naphthyl) ) -1,3,4-thiadiazole, 1,4-bis 2- (5-phenylthiadiazolyl)] benzene, 2- (4′-tert-butylphenyl) -5- (4 ″ -biphenyl) -1,3,4-triazole, 2,5-bis (1- Naphthyl) -1,3,4-triazole, 1,4-bis [2- (5-phenyltriazolyl)] benzene and the like are exemplified, but not limited thereto.

In the organic EL device of the present invention, if the electron injection / transport layer is made of an insulator or a semiconductor, current leakage can be effectively prevented and electron injection can be improved.
The insulator is preferably at least one metal compound selected from the group consisting of alkali metal chalcogenides, alkaline earth metal chalcogenides, alkali metal halides and alkaline earth metal halides. If the electron injection layer is composed of these alkali metal chalcogenides or the like, it is preferable in that the electron injection property can be further improved.

Examples of the alkali metal chalcogenide include Li ₂ O, LiO, Na ₂ S, Na ₂ Se, and NaO. Examples of the alkaline earth metal chalcogenide include CaO, BaO, SrO, BeO, BaS, and the like. Examples of the alkali metal halide include LiF, NaF, KF, LiCl, KCl, and NaCl. Preferred examples of the alkaline earth metal halide include CaF ₂ and BaF _2. , fluorides such as _SrF 2, MgF ₂ and BeF _2, and halides other than fluorides.
Examples of the semiconductor include oxide, nitride, or oxynitride containing at least one element of Ba, Ca, Sr, Yb, Al, Ga, In, Li, Na, Cd, Mg, Si, Ta, Sb, and Zn. Or a combination of two or more.

  The inorganic compound as the material of the electron injecting / transporting layer is preferably a microcrystalline or amorphous insulating thin film. If the electron transport layer is composed of these insulating thin films, a more uniform thin film is formed, and pixel defects such as dark spots can be reduced. Examples of such inorganic compounds include the alkali metal chalcogenides, alkaline earth metal chalcogenides, alkali metal halides, and alkaline earth metal halides described above.

  Furthermore, in the organic EL device of the present invention, the electron injection / transport layer may contain a reducing dopant having a work function of 2.9 eV or less. Here, the reducing dopant is defined as a substance capable of reducing the electron transporting compound. Accordingly, various materials can be used as long as they have a certain reducibility, such as alkali metals, alkaline earth metals, rare earth metals, alkali metal oxides, alkali metal halides, alkaline earth metals. At least selected from the group consisting of oxides, halides of alkaline earth metals, oxides of rare earth metals or halides of rare earth metals, organic complexes of alkali metals, organic complexes of alkaline earth metals, organic complexes of rare earth metals One substance can be preferably used.

Among these, preferable reducing dopants include Na (work function: 2.36 eV), K (work function: 2.28 eV), Rb (work function: 2.16 eV), and Cs (work function: 1.95 eV). And at least one alkali metal selected from the group consisting of Ca (work function: 2.9 eV), Sr (work function: 2.0 to 2.5 eV), and Ba (work function: 2.52 eV). Examples include at least one alkaline earth metal selected from the group, and a work function of 2.9 eV is particularly preferable.
A more preferred reducing dopant is at least one alkali metal selected from the group consisting of K, Rb and Cs, particularly preferably Rb or Cs, and most preferably Cs. These alkali metals have particularly high reducing ability, and by adding a relatively small amount to the electron injecting / transporting layer, the luminance of the organic EL element can be improved and the life can be extended.

  Further, as a reducing dopant having a work function of 2.9 eV or less, a combination of two or more of the above-mentioned alkali metals is also preferable. In particular, a combination containing Cs, for example, Cs and Na, Cs and K, Cs And a combination of Rb or Cs, Na and K. By including Cs in combination, the reducing ability can be efficiently exhibited, and by adding to the electron injecting / transporting layer, the luminance of the organic EL element can be improved and the lifetime can be extended.

(4) Other layers It is also preferable to provide a sealing layer for preventing moisture and oxygen from entering the organic EL element 1 so as to cover the entire organic EL element 1. As a preferable material for the sealing layer, a copolymer obtained by copolymerizing a monomer mixture containing tetrafluoroethylene and at least one comonomer; a fluorinated copolymer having a cyclic structure in the copolymer main chain; Examples include polyethylene, polypropylene, polymethyl methacrylate, polyimide, polyurea, polytetrafluoroethylene, polychlorotrifluoroethylene, polydichlorodifluoroethylene, or a copolymer of chlorotrifluoroethylene and dichlorodifluoroethylene.

Further, preferable sealing layer materials include a water-absorbing substance having an absorption rate of 1% or more; a moisture-proof substance having a water absorption rate of 0.1% or less; In, Sn, Pb, Au, Cu, Ag, Al, Ti, Ni Metal oxides such as MgO, SiO, SiO ₂ , GeO, NiO, CaO, BaO, Fe ₂ O, Y ₂ O ₃ , TiO ₂ ; Metal fluorides such as MgF ₂ , LiF, AlF ₃ , and CaF ₂ And liquid fluorinated carbon such as perfluoroalkane, perfluoroamine, and perfluoropolyether; and a composition in which an adsorbent that adsorbs moisture and oxygen is dispersed in the liquid fluorinated carbon.

  In forming the sealing layer, vacuum deposition, spin coating, sputtering, casting, MBE (molecular beam epitaxy), cluster ion beam deposition, ion plating, plasma polymerization (high frequency excitation) An ion plating method), a reactive sputtering method, a plasma CVD method, a laser CVD method, a thermal CVD method, a gas source CVD method, and the like can be appropriately employed.

Since the organic EL device of the present invention has an anode made of the transparent electrode of the present invention, the organic EL device has excellent adhesion to other layers and has a long life because of little deterioration.
In the organic EL device of the present invention formed by spin coating an aqueous solution of an organic polymer material on the anode buffer layer adjacent to the anode, the anode is not dissolved even if the dopant anion of the organic polymer material is acidic. The organic EL device can be produced efficiently and economically without producing dark spots.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

<Manufacture of transparent electrodes>
Example 1
(1) Production of Sputtering Target Powder of indium oxide (In ₂ O ₃ ) and cerium oxide (CeO ₂ ) (each average particle diameter of 1 μm or less) was changed to a weight ratio of In ₂ O ₃ : CeO ₂ of 95: 5. Thus, it was accommodated in a wet ball mill container and mixed and ground for 72 hours. Next, the obtained pulverized product was granulated and then press-molded into a size of 4 inches in diameter and 5 mm in thickness. This was accommodated in a firing furnace and then heated and fired at a temperature of 1400 ° C. for 36 hours to produce a target for producing a transparent electrode.

(2) Production of transparent electrode Next, a transparent glass substrate having a thickness of 1.1 mm, a length of 25 mm, and a width of 75 mm in a vacuum chamber shared by the high-frequency sputtering apparatus and the vacuum deposition apparatus, and the target obtained in the above (1) And a high-frequency sputtering apparatus was operated to form a transparent conductive film having a thickness of 75 nm to obtain a substrate with an anode. In addition, in a state where the degree of vacuum is reduced to 3 × 10 ⁻¹ Pa, a gas in which oxygen gas is mixed into argon gas is sealed, and in this atmosphere, the ultimate vacuum is 5 × 10 ⁻⁴ Pa, the substrate temperature is 25 ° C., Sputtering was performed under the conditions of an input power of 100 W and a film formation time of 14 minutes. Subsequently, the substrate was ultrasonically cleaned with isopropyl alcohol, further dried in an N ₂ (nitrogen gas) atmosphere, and then cleaned with UV (ultraviolet light) and ozone for 10 minutes. In this state, the oxidation-reduction potential of the transparent conductive film on the substrate was measured and found to be 0.24V.

Examples 2 to 8, Reference Example 1 and Comparative Example 1
A sputtering target was prepared in the same manner as in Example 1 except that the type and amount of the metal oxide used for producing the sputtering target were changed as shown in Table 1 below, a transparent conductive film was formed, and a substrate with an anode Got. In addition, Table 1 below shows the redox potential of the transparent conductive film in the obtained substrate.

<Manufacture of organic EL elements>
Example 9
The substrate with an anode obtained in Example 1 was mounted on a substrate holder of a vacuum chamber, and then the inside of the vacuum chamber was depressurized until the degree of vacuum was 1 × 10 ⁻⁶ Torr or less, and then on the anode layer 10 of the substrate. Then, an anode buffer layer 12, a light emitting layer 14, an electron injection layer, and a cathode layer 18 were sequentially laminated to obtain an organic EL device. At this time, the same vacuum conditions were applied between the formation of the organic light emitting layer 14 and the formation of the cathode layer 18 without breaking the vacuum state.

(1) Formation of anode buffer layer The transparent electrode film was subjected to photolithography and etching treatment to form a 2 mm wide strip-shaped hole injection electrode. The glass substrate on which the hole injection electrode was formed was ultrasonically washed with acetone and IPA (2-propanol) for 10 minutes each and then dried.
Next, a 65 nm hole transport layer was formed with a spin coater using the hole transport layer forming coating solution. Here, as the hole transport layer forming coating solution, a solution in which PEDOT / PSS (5 mg / 95 mg) was dispersed in pure water (10 ml) was used.
Next, this substrate was heat-dried at 200 ° C. for 5 minutes in a high-purity nitrogen atmosphere to remove the solvent in the hole transport layer.
The film thickness of the anode buffer layer thus formed was 10 nm.

(2) Formation of light emitting layer Next, a 70 nm light emitting layer was formed on the hole transport layer using a spin coater, using an electron transporting light emitting layer forming coating solution. Here, as a coating liquid for forming an electron transporting light emitting layer, poly (2-methoxy-5- (2′-ethylhexyloxy) -1,4-phenylenevinylene) (hereinafter referred to as MEH-PPV) (100 mg) is xylene. A solution dissolved in 10 ml was used.
Next, this substrate was heat-dried in a high-purity nitrogen atmosphere at 90 ° C. for 1 hour to remove the solvent in the layer.

(3) Formation of electron injection / transport layer After that, a glass substrate on which a hole injection electrode, a hole transport layer and a light emitting layer are formed is placed in a vacuum deposition apparatus for electrode formation, and a stainless steel metal is formed on the light emitting layer. Ca was formed to have a film thickness of 2.5 nm as an electron injection electrode by a vacuum deposition method using a mask, and subsequently, Al was formed to have a film thickness of 100 nm.
In this way, an electron injection electrode composed of a 2 mm wide strip-like Ca / Al layer orthogonal to the hole injection electrode was formed, and an organic EL device was obtained.
Finally, the sealing glass was bonded to a glass substrate so as to cover the organic EL element using a UV curable resin.

(5) Evaluation of organic EL element In the obtained organic EL element, the cathode layer 18 was used as a minus (-) electrode and the anode layer 10 was used as a plus (+) electrode, and a DC voltage of 5.5 V was applied between both electrodes. It was confirmed that the current density at this time was 4.5 mA / cm ² . Furthermore, as a durability evaluation, when it was driven at a constant current of 100 cd / m ² , it had a driving life of 820 hours.
Moreover, when the number of dark spots within a range of 2 mm × 2 mm was confirmed by visual check with a microscope, it was only two.

Examples 10 to 20, Reference Example 2 and Comparative Examples 2 to 5
An organic EL device was produced in the same manner as in Example 9 except that an anode buffer layer was formed using an anode and a hole injection material having the configuration shown in Table 2 below, and the performance was evaluated. The results are shown in Table 2 below.
The following hole injecting materials used in each example were prepared as follows and applied onto the transparent electrode by a spin coating method.
(1) PVK ⁺ ClO ₄ ⁻
After adjusting the chlorobenzene solution (0.3 wt%) of PVK-ClO ₄ so that the molar ratio of nitrogen in PVK to Cl in perchloric acid is 1: 0.3, it is filtered through a 0.45 micron filter. did.
(2) PANI-CSA
After preparing an ethanol solution (0.5 wt%) of PANI-CSA so that the molar ratio of nitrogen in polyaniline (PANI) and sulfur in camphorsulfonic acid (CSA) was 1: 0.5, 0. Filtration through a 45 μm filter.
(3) SSPY-TCNA
A 0.5 wt% solution of NMP (N-methylpyrrolidone) was prepared using SSPY-TCNA manufactured by TA Chemical Co., Ltd.
(4) PANI ⁺ BF ₄ ⁻
After preparing a chlorobenzene solution (0.3 wt%) of PVK-ClO ₄ so that the molar ratio of nitrogen in PANI to Cl in perchloric acid was 1: 0.3, it was filtered through a 0.45 micron filter. did.

  From the results in Table 2, since the transparent electrode (anode) of the present invention is excellent in acid resistance, the anode buffer layer was formed from a highly acidic organic polymer material such as PEDOT / PSS by a wet method. However, it can be seen that the generation of dark spots is suppressed and the driving life is improved.

The organic EL element using the transparent electrode of the present invention as an anode can simplify the manufacturing process because the anode is excellent in smoothness. In addition, since the anode is excellent in acid resistance, an anode buffer layer can be easily and economically formed by a wet method even when an organic polymer material such as PEDOT / PSS with high acidity is used. Can do. Therefore, since it is not necessary to use crystalline ITO that is an expensive anode material that is conventionally used in combination with PEDOT / PSS and requires a polishing step, it is very advantageous in terms of industrial economy.
ADVANTAGE OF THE INVENTION According to this invention, a dark spot does not generate | occur | produce, and since the adhesiveness of an anode and another layer is high, the organic EL element with a long drive life can be provided.
The organic EL device of the present invention is highly useful and is extremely useful as a flat light emitter such as a flat panel display, a light source such as a copying machine, a printer, a backlight of a liquid crystal display or a computer, a display board, a marker lamp, etc. It is.

It is a schematic diagram which shows one Embodiment of the organic EL element of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Organic EL element 10 Anode 12 Anode buffer layer 14 Light emitting layer 18 Cathode

Claims (14)

  In a polar solvent at 25 ° C. in which the supporting electrolyte is dissolved, when the oxidation-reduction potential of crystalline ITO is E (V), the oxidation-reduction potential is (E−0.1) V or more, (E + 1.0) A transparent conductive film other than crystalline ITO in the range of V or less.   An oxide of at least one metal selected from indium, zinc and tin, and aluminum, titanium, vanadium, manganese, iron, cobalt, nickel, copper, gallium, germanium, strontium, niobium, molybdenum, palladium, silver, antimony The transparent conductive film according to claim 1, comprising a mixture of oxides of at least one element selected from the group consisting of barium, hafnium, tantalum, tungsten, iridium, and rare earth elements.   (A) at least one metal oxide selected from indium, zinc, and tin; and (B) at least one metal selected from aluminum, titanium, molybdenum, tantalum, tungsten, cerium, samarium, gadolinium, and neodymium. The transparent conductive film of Claim 2 which consists of a mixture with the oxide of these elements.   The ratio (A) :( B) (weight ratio) of the said metal oxide (A) and the said metal oxide (B) exists in the range of 50-90: 10-50, The transparent electroconductivity of Claim 3 film.   The transparent electrode for organic electroluminescent elements which consists of a transparent conductive film of any one of Claims 1-4.   An oxide of at least one metal selected from indium, zinc and tin, and aluminum, titanium, vanadium, manganese, iron, cobalt, nickel, copper, gallium, germanium, strontium, niobium, molybdenum, palladium, silver, antimony A sputtering target comprising a mixture of oxides of at least one element selected from tantalum, barium, hafnium, tantalum, tungsten, iridium, and rare earth elements.   (A) at least one metal oxide selected from indium, zinc, and tin; and (B) at least one metal selected from aluminum, titanium, molybdenum, tantalum, tungsten, cerium, samarium, gadolinium, and neodymium. The sputtering target according to claim 6, comprising a mixture with an oxide of the element.   The ratio (A) :( B) (weight ratio) of the said metal oxide (A) and the said metal oxide (B) exists in the range of 50-90: 10-50, The sputtering target of Claim 7 .   6. An organic electroluminescence device comprising a plurality of organic thin film layers including at least a light emitting layer sandwiched between a cathode and an anode, wherein the transparent electrode according to claim 5 is used as an anode.   The organic electroluminescence device according to claim 9, further comprising an anode buffer layer adjacent to the anode, wherein the anode buffer layer is made of an organic polymer material.   The organic electroluminescence device according to claim 10, wherein a dopant anion of the organic polymer material is acidic in a polar solvent.   The organic electroluminescence device according to claim 10 or 11, wherein the organic polymer material is polyethylene dioxythiophene / polystyrene sulfonic acid (PEDOT / PSS) or polyaniline / camphor sulfonic acid (PANI / CSA).   The organic electroluminescent element according to claim 10, wherein the anode buffer layer has a thickness of 1 nm to 500 nm. The method for producing an organic electroluminescent element according to claim 10, wherein the anode buffer layer is formed by spin-coating an aqueous solution of an organic polymer material on the anode.

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