JP2015146438A - Electron-accepting dopant for organic electroluminescent element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electron-accepting dopant for an organic electroluminescent element, having high solubility to an organic solvent, high oxidizability to a charge transport host material in a hole injection layer, and oxidizability to a hole transport material.SOLUTION: An electron-accepting dopant for an organic electroluminescent element comprises a heteropoly acid compound.

Description

  The present invention relates to an electron-accepting dopant for an organic electroluminescence device, and more particularly to an electron-accepting dopant for an organic electroluminescence device comprising a heteropolyacid compound.

Conventionally, in a low molecular organic electroluminescence (hereinafter abbreviated as OLED) element, by providing a copper phthalocyanine (CuPC) layer as a hole injection layer, an initial characteristic improvement such as a decrease in driving voltage and an improvement in luminous efficiency, and a lifetime are achieved. It has been reported that characteristic improvement can be realized (Non-Patent Document 1).
Moreover, it has been reported that a drive voltage can be lowered by forming a thin film by vacuum-depositing a metal oxide and using it as a hole injection layer (Non-patent Document 2).

  On the other hand, in an organic electroluminescence (hereinafter abbreviated as PLED) element using a polymer light emitting material, a thin film made of a polyaniline-based material (Patent Document 1, Non-Patent Document 3) or a polythiophene-based material (Non-Patent Document 4) is used. It has been reported that the same effect as an OLED element can be obtained by using it as a hole transport layer.

In recent years, a charge transporting varnish comprising a homogeneous solution completely dissolved in an organic solvent using a highly soluble low molecular weight oligoaniline material or oligothiophene material has been found. And, it has been reported that by inserting a hole injection layer obtained from this varnish into an organic electroluminescence (hereinafter referred to as organic EL) element, a planarization effect of the base substrate and excellent EL element characteristics can be obtained. (Patent Document 2, Patent Document 3).
The low molecular weight oligomer compound itself has a low viscosity, and when a normal organic solvent is used, the process margin in the film forming operation is narrow. Therefore, various coating methods such as spin coating, inkjet coating, spray coating, etc. When using the above baking conditions, it was difficult to form a film having high uniformity.
In this regard, by using various additive solvents, it is possible to adjust the viscosity, boiling point and vapor pressure, and it has become possible to obtain a film-forming surface having high uniformity corresponding to various coating methods. (Patent Literature 4, Patent Literature 5).

However, now that the full-scale mass production of the organic EL device is about to start, further reduction in the driving voltage of the element is required.
On the other hand, in recent years, hole injection layers using metal oxides have been reviewed, and the metal oxide forming the hole injection layer oxidizes the interface upon contact with the hole transport layer, thereby generating holes. It has been reported that a doping layer can be formed in the transport layer and the driving voltage can be lowered (Non-Patent Document 5, Non-Patent Document 6). There is no need to develop new materials.

JP-A-3-230787 JP 2002-151272 A International Publication No. 2005/043962 International Publication No. 2004/043117 International Publication No. 2005/107335

Applied Physics Letters, USA, 1996, 69, p. 2160-2162 Journal of Physics D: Applied Physics D, UK, 1996, 29, p. 2750-2753 Nature, UK, 1992, 357, p. 477-479 Applied Physics Letters, USA, 1998, 72, p. 2660-2662 Applied Physics Letters, USA, 2007, Vol. 91, p. 253504 Applied Physics Letters, USA, 2008, 93, p. 043308

  The present invention has been made in view of such circumstances, and has high solubility in an organic solvent, high oxidation property for a charge transporting host material in a hole injection layer, and further oxidation property for a hole transport material. Another object of the present invention is to provide an electron-accepting dopant for an organic electroluminescence device.

As a result of intensive studies to achieve the above object, the present inventors have found that heteropolyacid compounds such as phosphomolybdic acid have high solubility in organic solvents and high oxidation of charge transporting host materials in the hole injection layer. When the charge transporting thin film containing the heteropoly acid compound and the charge transporting substance is used as the hole injection layer of the OLED element, The present inventors have found that the drive voltage can be lowered and the device life can be improved, and the present invention has been completed.
A heteropolyacid compound such as phosphomolybdic acid typically has a Keggin-type chemical structure represented by Chemical Formula 1 or a Dawson-type chemical structure represented by Chemical Formula 2, that is, a structure in which a heteroatom is located at the center of the molecule. .

Due to these special chemical structures, there are significant differences in solubility and oxidation-reduction characteristics from isopolyacids and simple metal oxides composed only of metal oxygen acids. Conventionally, this compound has been well known as a polymerization catalyst or a color reagent for organic compounds, but there are few examples in which the compound itself is used as a charge transporting substance.
The present inventors have found that this heteropolyacid compound functions as an effective hole injection layer by forming a layer with an ultrathin film in an organic EL device.

That is, the present invention
1. An electron-accepting dopant for an organic electroluminescence device, comprising a heteropolyacid compound,
2. 1 electron-accepting dopant, wherein the heteropolyacid compound is phosphomolybdic acid, silicomolybdic acid, phosphotungstic acid, phosphotungstomolybdic acid or silicotungstic acid;
3. 1 or 2 electron-accepting dopants for a hole injection layer or a hole transport layer of an organic electroluminescence device,
4). Three electron-accepting dopants for a hole injection layer of an organic electroluminescence device are provided.

The heteropolyacid compound contained in the charge transporting material of the present invention has good solubility in an organic solvent used for the preparation of a general charge transporting varnish, and in particular, once dissolved in a good solvent. By doing so, it exhibits excellent solubility in various organic solvents including high viscosity solvents and low surface tension solvents. For this reason, it is possible to prepare a low-polarity organic solvent-based charge transporting varnish by using a part or almost all of a high viscosity solvent or a low surface tension solvent.
Such a low-polarity organic solvent-based charge transporting varnish can be applied not only by an inkjet coating apparatus in which solvent resistance is a problem, but also has a problem of solvent resistance such as an insulating film and partition walls on the substrate. Even when a structure exists, it can be used. As a result, an amorphous solid thin film having high flatness can be produced without any problem.
Furthermore, since the obtained thin film exhibits high charge transportability, it can be used as a hole injection layer or a hole transport layer, thereby reducing the driving voltage of the organic EL device and extending the life of the device. be able to.
Since heteropoly acid compounds generally have a high refractive index, an improvement in light extraction efficiency can be expected by an effective optical design.
In addition, since this thin film has high flatness and high charge transport properties, this thin film can be used to protect a buffer layer or a hole transport layer of a solar cell, an electrode for a fuel cell, a capacitor electrode, using this property. It can also be applied to films and antistatic films.

Hereinafter, the present invention will be described in more detail.
The charge transport material according to the present invention contains a charge transport material and a heteropolyacid compound as an electron accepting dopant. The charge transporting substance is also referred to as a charge transporting host substance when used in combination with an electron accepting dopant.
Here, the charge transportability is synonymous with conductivity, and means any one of hole transportability, electron transportability, and both charge transportability of holes and electrons. The charge transporting material of the present invention may itself have a charge transporting property, or the solid film obtained therefrom may have a charge transporting property.

The heteropolyacid compound is a polyacid formed by condensing an isopolyacid that is an oxygen acid such as vanadium (V), molybdenum (Mo), or tungsten (W) and an oxyacid of a different element.
In this case, the oxygen acid of the different element mainly includes silicon (Si), phosphorus (P), and arsenic (As) oxygen acids.

Specific examples of the heteropolyacid compound include phosphomolybdic acid, silicomolybdic acid, phosphotungstic acid, phosphotungstomolybdic acid, silicotungstic acid, etc. In the present invention, high solubility in organic solvents, charge transportability From the viewpoints of high oxidizability with respect to substances and reduction in driving voltage and improvement in life when used in an organic EL device, phosphomolybdic acid, phosphotungstic acid, and phosphotungstomolybdic acid are preferred, and phosphomolybdic acid is particularly preferred.
These heteropolyacid compounds are available as commercial products. For example, phosphomolybdic acid (Phosphobomobic acid hydrate, or 12 Polybodo (VI) phosphoric acid n-hydrate, chemical formula: H ₃ (PMo ₁₂ O ₄₀ ). nH ₂ O) is available from Kanto Chemical Co., Inc., Wako Pure Chemical Industries, Ltd., Sigma-Aldrich Japan Co., Ltd. and the like.

The charge transporting material that can be used in the charge transporting material of the present invention is not particularly limited as long as it is soluble in the organic solvent to be used, but when used for organic EL applications, it is 100 nm or less, usually 20 Since it is necessary to produce a very thin film of about 50 nm in a highly uniform manner, the charge transporting material preferably has high solubility, and preferably has no molecular weight distribution in order to suppress mixing of impurity components, and particularly has a molecular weight of 200 to 2000. The low molecular weight compound is preferred. Since low-molecular compounds have low viscosity and are often difficult to form uniformly and uniformly, it is desirable to use a high-viscosity solvent together. It is desirable to have the solubility.
Specifically, an aniline derivative compound such as a low-molecular oligoaniline compound, a low-molecular oligothiophene compound, or the like conventionally used as a highly soluble material can be used.
Since the heteropolyacid compound contains a protonic acid and exerts a function as an electron accepting substance strongly against a charge transporting substance containing an NH group, an aniline derivative compound is suitable as the charge transporting substance, In view of higher charge transportability, an oligoaniline derivative compound having 3 or more aniline units is more preferable.
That is, a heteropolyacid compound usually has two or more protic hydrogens, and forms an ionic pseudopolymer with an oligoaniline derivative compound containing a plurality of NH groups. Migration is suppressed and the lifetime is easily improved. Further, as will be described later, since the heteropolyacid compound also has an oxidizability with respect to the triphenylamine-containing compound, when this is used for the hole injection layer, the charge transporting host material in the hole injection layer and In addition, it is possible to oxidize the material contained in the adjacent hole transport layer.

  In particular, since it has high solubility and high charge transportability and has an appropriate ionization potential, it is an oligoaniline derivative represented by the following formula (1), or a quinonediimine that is an oxidant of formula (1) Derivatives can be preferably used, and are further represented by the formula (4) or (5) from the viewpoints of solubility, charge transportability, ionization potential (Ip) and oxidizability to the heteropolyacid compound of the present invention. Oligoaniline derivatives, or quinonediimine derivatives that are oxidants thereof are most suitable.

[Wherein R ¹ , R ² and R ³ are each independently a hydrogen atom, halogen atom, hydroxyl group, amino group, silanol group, thiol group, carboxyl group, phosphate group, phosphate ester group, ester group A thioester group, an amide group, a nitro group, a monovalent hydrocarbon group, an organooxy group, an organoamino group, an organosilyl group, an organothio group, an acyl group, or a sulfone group. The divalent group represented by Formula (2) or (3) is shown.

(Wherein R ^{4 to} R ¹¹ are each independently a hydrogen atom, halogen atom, hydroxyl group, amino group, silanol group, thiol group, carboxyl group, phosphate group, phosphate ester group, ester group, thioester group) Amide group, nitro group, monovalent hydrocarbon group, organooxy group, organoamino group, organosilyl group, organothio group, acyl group, or sulfone group.)
m and n are each independently an integer of 1 or more and satisfy m + n ≦ 20. ]

(In the formula, R ^{1 to} R ⁷ , m and n have the same meaning as described above.)

(In the formula, R ² , R ^{4 to} R ⁷ , R ^{12 to} R ³⁵ , n and m represent the same meaning as described above.)

  In addition, a quinone diimine body means the compound which has the partial structure shown by a following formula in the frame | skeleton.

(Wherein R ^{4 to} R ⁷ are the same as above)

In the above formulas, examples of the halogen atom include fluorine, chlorine, bromine and iodine atoms.
Specific examples of monovalent hydrocarbon groups include methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, t-butyl, n-hexyl, and n-octyl. Group, alkyl group such as 2-ethylhexyl group and decyl group; cycloalkyl group such as cyclopentyl group and cyclohexyl group; bicycloalkyl group such as bicyclohexyl group; vinyl group, 1-propenyl group, 2-propenyl group and isopropenyl group , 1-methyl-2-propenyl group, alkenyl group such as 1 or 2 or 3-butenyl group, hexenyl group; aryl group such as phenyl group, xylyl group, tolyl group, biphenyl group, naphthyl group; benzyl group, phenylethyl Group, aralkyl groups such as phenylcyclohexyl group, etc., or some or all of the hydrogen atoms of these monovalent hydrocarbon groups are halogenated Child, a hydroxyl group, an alkoxy group include those substituted with a sulfonic group.

Specific examples of the organooxy group include an alkoxy group, an alkenyloxy group, and an aryloxy group, and examples of the alkyl group, alkenyl group, and aryl group include the same groups as those exemplified above.
Specific examples of the organoamino group include phenylamino group, methylamino group, ethylamino group, propylamino group, butylamino group, pentylamino group, hexylamino group, heptylamino group, octylamino group, nonylamino group, decylamino group. Alkylamino groups such as laurylamino group; dimethylamino group, diethylamino group, dipropylamino group, dibutylamino group, dipentylamino group, dihexylamino group, diheptylamino group, dioctylamino group, dinonylamino group, didecylamino group, etc. A dialkylamino group; a cyclohexylamino group, a morpholino group, and the like.

Specific examples of the organosilyl group include trimethylsilyl group, triethylsilyl group, tripropylsilyl group, tributylsilyl group, tripentylsilyl group, trihexylsilyl group, pentyldimethylsilyl group, hexyldimethylsilyl group, octyldimethylsilyl group, Examples include decyldimethylsilyl group.
Specific examples of the organothio group include alkylthio groups such as methylthio group, ethylthio group, propylthio group, butylthio group, pentylthio group, hexylthio group, heptylthio group, octylthio group, nonylthio group, decylthio group and laurylthio group.

Specific examples of the acyl group include formyl group, acetyl group, propionyl group, butyryl group, isobutyryl group, valeryl group, isovaleryl group, benzoyl group and the like.
Examples of the phosphate ester group include -P (O) (OQ ¹ ) (OQ ² ).
Examples of the ester group include —C (O) OQ ¹ and —OC (O) Q ¹ .
Examples of the thioester group include —C (S) OQ ¹ and —OC (S) Q ¹ .
Examples of the amide group include —C (O) NHQ ¹ , —NHC (O) Q ¹ , —C (O) NQ ¹ Q ² , and —NQ ¹ C (O) Q ² .
Here, Q ¹ and Q ² represent an alkyl group, an alkenyl group, or an aryl group, and examples thereof include the same groups as those exemplified for the monovalent hydrocarbon group.

The number of carbon atoms in the monovalent hydrocarbon group, organooxy group, organoamino group, organosilyl group, organothio group, acyl group, phosphate ester group, ester group, thioester group, and amide group is not particularly limited. Generally, it has 1 to 20 carbon atoms, preferably 1 to 8 carbon atoms.
Preferred substituents include fluorine, sulfone group, organooxy group, alkyl group, organosilyl group and the like.
In addition, in a substituent, substituents may be connected and the cyclic | annular part may be included.

In the general formulas (1), (4) and (5), m + n is preferably 3 or more from the viewpoint of exhibiting good charge transportability, and is 16 or less from the viewpoint of ensuring solubility in a solvent. Preferably there is.
In addition, the oligoaniline derivatives of the formulas (1) and (4) have no molecular weight distribution, in other words, an oligodispersity of 1 in view of increasing solubility and making charge transport properties uniform. An aniline derivative is preferred.
The molecular weight is usually 200 or more, preferably 300 or more as a lower limit for suppressing volatilization of the material and manifesting charge transport properties, and is usually 5000 or less, preferably 2000 or less as an upper limit for improving solubility. is there.
These charge transport materials may be used alone or in combination of two or more materials.
Specific examples of such a compound include N, N, N ′, N′-tetraphenyl-p-C-aminopentaaniline represented by the following formula (6), and N— represented by formula (7). Oligoaniline derivatives soluble in organic solvents such as phenyltrianiline, N-phenyltetraaniline represented by the formula (8), tetraaniline (aniline tetramer), octaaniline (aniline octamer) and the like can be mentioned.

The method for synthesizing these charge transporting substances is not particularly limited, but the method described in International Publication No. 2008/129947, oligoaniline synthesis method (Bulletin of Chemical Society of Japan (Bulletin of Chemical) Society of Japan), 1994, Vol. 67, p. 1749-1752, Synthetic Metals, USA, 1997, Vol. 84, p. 119-120), oligothiophene synthesis methods (for example, Heterocycles, 1987, Vol. 26, p. 939-942, Heterocycles, 1987, Vol. 26, p. 1793-1796) and the like.
Moreover, as a method of oxidizing an oligoaniline derivative compound into a quinonediimine compound, a method described in International Publication No. 2008/01047 may be mentioned.

A charge transporting varnish according to the present invention includes the charge transporting material described above, a charge transporting material configured to include a heteropolyacid compound as an electron-accepting dopant, and an organic solvent. The heteropolyacid compound is uniformly dissolved in an organic solvent.
As the organic solvent used when preparing the charge transporting varnish, a good solvent having the ability to dissolve the charge transporting substance and the heteropolyacid compound can be used.
Here, the good solvent means a solvent in which the polarity of the solvent molecule is high and the high polarity compound can be dissolved well.
Examples of such a good solvent include N, N-dimethylformamide, N, N-dimethylacetamide, N-methylpyrrolidone, 1,3-dimethyl-2-imidazolidinone, dimethyl sulfoxide, N-cyclohexyl-2- Examples include pyrrolidinone. These solvents can be used alone or in combination of two or more, and the amount used can be 5 to 100% by mass with respect to the total solvent used in the varnish.

Since the heteropolyacid compound used in the present invention is excellent in solubility in an organic solvent, a high viscosity solvent and / or a low surface tension solvent can be used together with the good solvent. The good solvent, the high-viscosity solvent, and the low surface tension solvent may each have properties of each other.
A high-viscosity solvent gives a viscosity suitable for spraying and coating in various coating devices to form a uniform wet film. During firing, it causes solvent volatilization while suppressing the aggregation of the wet film and the occurrence of irregularities. It means a solvent capable of forming a thin film having uniform film thickness uniformity.
Examples of the high-viscosity solvent include those having a viscosity of 10 to 200 mPa · s, particularly 50 to 150 mPa · s at 25 ° C., and specifically, those having a boiling point of 50 to 300 ° C., particularly 150 to 250 ° C. at normal pressure. Cyclohexanol, ethylene glycol, 1,3-octylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol, 1,3-butanediol, 2,3-butanediol, 1,4 which are high viscosity solvents -Butanediol, propylene glycol, hexylene glycol, o-cresol, m-cresol, p-cresol and the like are suitable.
When using these high-viscosity solvents, 10-90 mass% is preferable with respect to the whole solvent in a varnish, and 20-80 mass% is more preferable.

A low surface tension solvent means improved wettability to the substrate by reducing surface tension, imparting volatility, imparting physical properties suitable for spraying and coating in various coating devices, and reducing corrosivity to coating devices. It means the solvent that makes it possible.
Examples of such a low surface tension solvent include aromatic hydrocarbons such as benzene, toluene, ethylbenzene, p-xylene, o-xylene, and styrene; n-pentane, n-hexane, n-heptane, and n-octane. , N-nonane, n-decane and the like hydrocarbons; acetone, methyl ethyl ketone, methyl isopropyl ketone, diethyl ketone, methyl isobutyl ketone, methyl n-butyl ketone, cyclohexanone, ethyl n-amyl ketone, and the like; ethyl acetate, isopropyl acetate , Esters such as n-propyl acetate, i-butyl acetate, n-butyl acetate, n-amyl acetate, n-hexyl acetate, methyl caproate, 2-methylpentyl acetate, n-ethyl lactate, n-butyl lactate Ethylene glycol dimethyl ether, propylene glycol Methyl ether, ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, propylene glycol monoethyl ether, ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether, ethylene glycol methyl ether acetate, propylene glycol monomethyl ether acetate, ethylene glycol ethyl ether acetate, diethylene glycol Dimethyl ether, propylene glycol monobutyl ether, diethylene glycol diethyl ether, dipropylene glycol monomethyl ether, diethylene glycol monomethyl ether, dipropylene glycol monoethyl ether, diethylene glycol monoethyl ether, triethylene glycol dimethyl ether Glycol esters or glycol ethers such as ter, diethylene glycol monoethyl ether acetate, diethylene glycol; methanol, ethanol, isopropanol, t-butanol, allyl alcohol, n-propanol, 2-methyl-2-butanol, isobutanol, n-butanol, 2-methyl-1-butanol, 1-pentanol, 2-methyl-1-pentanol, 2-ethylhexanol, 1-octanol, 1-methoxy-2-butanol, diacetone alcohol, furfuryl alcohol, tetrahydrofurfuryl Alcohols such as alcohol and benzyl alcohol; diethyl ether, di-n-propyl ether, di-i-propyl ether, i-propyl ether, 1,4-dioxane, acetic acid, γ-butyl And ether or carboxylic acids such Rurakuton like.

When a good solvent and a high-viscosity solvent and / or a low surface tension solvent are used in combination, their use ratio is not particularly limited. Thus, it becomes possible to provide new preferable physical properties such as improvement in viscosity, reduction in surface tension, provision of volatility, improvement in paintability on the substrate surface, application, and improvement in sprayability. Moreover, as a result of the polarity of the obtained varnish being lowered, it becomes possible to use a coating apparatus, a substrate or the like in which solvent resistance is a problem, and the application range is expanded.
When a low surface tension solvent is used, the ratio of the good solvent to the high viscosity solvent and / or the low surface tension solvent is preferably about 9: 1 to 1: 9 by mass ratio, and 1: 1 to About 1: 4 is more preferable.
In addition, when two or more solvents are used as a mixture, the boiling point of the good solvent is desirably equal to or higher than that of other solvents.

The method for preparing the charge transporting varnish is not particularly limited and can be prepared by mixing each component and solvent in an arbitrary order. However, the above-mentioned heteropolyacid compound is once dissolved in a good solvent. In this case, the charge transporting substance and the heteropolyacid compound were dissolved in a good solvent because it has the property that precipitation does not easily occur even when a less viscous high viscosity solvent and / or a low surface tension solvent is added. It is preferable to prepare the solution by adding a high viscosity solvent and / or a low surface tension solvent.
When such a method is used, the ratio of the high viscosity solvent or the low surface tension solvent in the charge transporting varnish can be increased.

The solid content concentration of the charge transporting varnish is not particularly limited, but is usually about 0.01 to 50% by mass, and considering that a thin film of 0.1 to 200 nm is formed, 0.1% 10 mass% is preferable, and 0.5-5 mass% is more preferable.
In addition, the mixing ratio of the charge transporting substance and the heteropolyacid compound is not particularly limited. However, in consideration of further improving the charge transporting property of the obtained thin film, the charge transporting substance in mass ratio: Heteropoly acid compound = 1: 0.01-10.0 are preferable and 1: 0.05-4.0 are more preferable.
The viscosity of the charge transporting varnish is not particularly limited, but it is 25 considering that a thin film having a thickness of 0.1 to 200 nm is produced with high film thickness uniformity by a spin coating method, an ink jet method or a spray coating method. It is preferably 1 to 100 mPa · s, more preferably 3 to 30 mPa · s, and even more preferably 5 to 20 mPa · s at ° C.

In the charge transporting varnish of the present invention, in order to improve the charge transporting ability and the like, 0.1 to 90% by mass of a dopant substance other than the heteropolyacid compound described above is added to the charge transporting substance as necessary. You may use by the addition amount of a grade.
As the dopant material, an electron-accepting dopant material having a high electron-accepting property is preferable. The solubility of the dopant substance is not particularly limited as long as it is soluble in at least one solvent used for the varnish.

Specific examples of the electron-accepting dopant material include inorganic strong acids such as hydrogen chloride, sulfuric acid, nitric acid and phosphoric acid; aluminum chloride (III) (AlCl ₃ ), titanium tetrachloride (IV) (TiCl ₄ ), boron tribromide (BBr ₃ ), boron trifluoride ether complex (BF ₃ · OEt ₂ ), iron chloride (III) (FeCl ₃ ), copper (II) chloride (CuCl ₂ ), antimony pentachloride (V) (SbCl ₅ ), Lewis acids such as arsenic pentafluoride (V) (AsF ₅ ), phosphorus pentafluoride (PF ₅ ), tris (4-bromophenyl) aluminum hexachloroantimonate (TBPAH); benzenesulfonic acid, tosylic acid, camphorsulfonic acid Hydroxybenzenesulfonic acid, 5-sulfosalicylic acid, dodecylbenzenesulfonic acid, polystyrenesulfonic acid, International Publication No. 2005/000 Organic strong acids such as 1,4-benzodioxane disulfonic acid derivative described in No. 32, aryl sulfonic acid derivatives described in International Publication No. 2006/025342, dinonylnaphthalene sulfonic acid derivative described in JP-A-2005-108828; Examples include organic or inorganic oxidizing agents such as 7,8,8-tetracyanoquinodimethane (TCNQ), 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), and iodine. It is not limited to.

  Particularly preferred electron-accepting dopant materials include 5-sulfosalicylic acid, dodecylbenzenesulfonic acid, polystyrenesulfonic acid, 1,4-benzodioxane disulfonic acid derivatives described in WO2005 / 000832, and JP-A-2005-108828. Examples thereof include electron-accepting dopant materials which are strong organic acids such as dinonylnaphthalenesulfonic acid derivatives described above and naphthalenedisulfonic acid derivatives described in WO2006 / 025342.

A charge transporting thin film can be formed on a substrate by applying the charge transporting varnish described above on the substrate and evaporating the solvent.
The method for applying the varnish is not particularly limited, and examples thereof include a dipping method, a spin coating method, a transfer printing method, a roll coating method, a brush coating method, an ink jet method, a spray method, and a slit coating method.
The method for evaporating the solvent is not particularly limited. For example, the solvent may be evaporated in a suitable atmosphere, that is, in an inert gas such as air or nitrogen, in a vacuum, or the like using a hot plate or an oven. Thereby, a thin film having a uniform film formation surface can be obtained.
Although a calcination temperature will not be specifically limited if a solvent can be evaporated, It is preferable to carry out at 40-250 degreeC. In this case, two or more stages of temperature changes may be applied for the purpose of developing higher uniform film forming properties or allowing the reaction to proceed on the substrate.

  The thickness of the charge transporting thin film is not particularly limited, but is preferably 0.1 to 200 nm, more preferably 1 to 100 nm, and even more preferably 10 to 50 nm when used as a charge injection layer in an organic EL device. As a method of changing the film thickness, there are methods such as changing the solid content concentration in the varnish and changing the amount of the solution on the substrate during coating.

Examples of materials used and methods for producing an OLED element using the charge transporting varnish of the present invention include the following, but are not limited thereto.
The electrode substrate to be used is preferably cleaned in advance by cleaning with a detergent, alcohol, pure water, or the like. For example, the anode substrate is subjected to surface treatment such as ozone treatment or oxygen-plasma treatment immediately before use. Is preferred. However, when the anode material is mainly composed of an organic material, the surface treatment may not be performed.

When using a hole transporting varnish for an OLED element, the following method can be mentioned.
The hole transporting varnish is applied onto the anode substrate, evaporated and baked by the above method, and a hole transporting thin film is formed on the electrode to form a hole injection layer or a hole transport layer. This is introduced into a vacuum deposition apparatus, and a hole transport layer, a light emitting layer, an electron transport layer, an electron injection layer, and a cathode metal are sequentially deposited to form an OLED element. However, the element may be manufactured by removing any one layer or plural layers as necessary. In order to control the light emitting region, a carrier block layer may be provided between arbitrary layers.
Examples of the anode material include transparent electrodes typified by indium tin oxide (ITO) and indium zinc oxide (IZO), and those subjected to planarization treatment are preferable. Polythiophene derivatives and polyaniline derivatives having high charge transporting properties can also be used.

As a material for forming the hole transport layer, (triphenylamine) dimer derivative (TPD), (α-naphthyldiphenylamine) dimer (α-NPD), [(triphenylamine) dimer] spiro-dimer (Spiro-TAD) Triarylamines such as 4,4 ′, 4 ″ -tris [3-methylphenyl (phenyl) amino] triphenylamine (m-MTDATA), 4,4 ′, 4 ″ -tris [1-naphthyl (phenyl) ) Starburstamines such as amino] triphenylamine (1-TNATA), 5,5 ″ -bis- {4- [bis (4-methylphenyl) amino] phenyl} -2,2 ′: 5 ′, 2 And oligothiophenes such as “-terthiophene (BMA-3T)”.
The hole transport material having reducibility with respect to the heteropolyacid compound used in the present invention is preferable from the viewpoint of lowering the driving voltage in the organic EL device characteristics. In particular, triphenylamines, triarylamines or starburst amines are easily oxidized by the heteropolyacid compound used in the present invention. Therefore, the layer containing these compounds is used as the hole injection layer containing the heteropolyacid compound. It is preferable to use it as an adjacent hole transport layer.

Examples of the material for forming the light emitting layer include tris (8-quinolinolato) aluminum (III) (Alq ₃ ), bis (8-quinolinolato) zinc (II) (Znq ₂ ), bis (2-methyl-8-quinolinolato) ( p-phenylphenolate) aluminum (III) (BAlq) and 4,4′-bis (2,2-diphenylvinyl) biphenyl (DPVBi), and the like. The light emitting layer may be formed by co-evaporation.
As an electron transport material, Alq ₃ , BAlq, DPVBi, (2- (4-biphenyl) -5- (4-t-butylphenyl) -1,3,4-oxadiazole) (PBD), triazole derivatives ( TAZ), bathocuproine (BCP), silole derivatives and the like.

Examples of the luminescent dopant include quinacridone, rubrene, coumarin 540, 4- (dicyanomethylene) -2-methyl-6- (p-dimethylaminostyryl) -4H-pyran (DCM), tris (2-phenylpyridine) iridium ( III) (Ir (ppy) ₃ ), (1,10-phenanthroline) -tris (4,4,4-trifluoro-1- (2-thienyl) -butane-1,3-dionate) europium (III) ( Eu (TTA) ₃ phen) and the like.

Examples of the material for forming the carrier block layer include PBD, TAZ, and BCP.
Materials for forming the electron injection layer include lithium oxide (Li ₂ O), magnesium oxide (MgO), alumina (Al ₂ O ₃ ), lithium fluoride (LiF), magnesium fluoride (MgF ₂ ), and strontium fluoride. (SrF ₂ ), Liq, Li (acac), lithium acetate, lithium benzoate and the like.
Examples of the cathode material include aluminum, magnesium-silver alloy, aluminum-lithium alloy, lithium, sodium, potassium, cesium and the like.

Moreover, when using an electron transport varnish for an OLED element, the following method can be mentioned.
An electron transporting varnish is applied onto a cathode substrate to produce an electron transporting thin film, which is introduced into a vacuum deposition apparatus, and using the same materials as described above, an electron transporting layer, a light emitting layer, and a hole transporting layer After forming the hole injection layer, the anode material is deposited by a method such as sputtering to obtain an OLED element.

Although the manufacturing method of the PLED element using the charge transportable varnish of this invention is not specifically limited, The following methods are mentioned.
In the preparation of the OLED element, the charge transporting varnish of the present invention is formed by forming a light emitting charge transporting polymer layer instead of performing vacuum deposition operation of the hole transport layer, the light emitting layer, the electron transport layer, and the electron injection layer. A PLED element including a charge transporting thin film formed by the above can be produced.
Specifically, on the anode substrate, the charge transporting varnish (hole transporting varnish) of the present invention is applied to prepare a hole transporting thin film by the above-described method, and a luminescent charge transporting property is high on the upper part. A molecular layer is formed, and a cathode electrode is further deposited to form a PLED element. An interlayer may be provided between the hole transporting thin film and the light emitting polymer layer in order to improve light emission efficiency and device lifetime.

As the cathode and anode material to be used, the same substances as those used in the production of the OLED element can be used, and the same cleaning treatment and surface treatment can be performed.
As a method for forming the light emitting charge transporting polymer layer, a solvent is added to the light emitting charge transporting polymer material or a material obtained by adding a light emitting dopant to the material, and the solution is dissolved or evenly dispersed to inject holes. An example is a method in which a film is formed by evaporation of a solvent after application to an electrode substrate on which a layer is formed.
Examples of the light-emitting charge transporting polymer material include polyfluorene derivatives such as poly (9,9-dialkylfluorene) (PDAF), and poly (2-methoxy-5- (2′-ethylhexoxy) -1,4-phenylenevinylene. And polyphenylene vinylene derivatives such as (MEH-PPV), polythiophene derivatives such as poly (3-alkylthiophene) (PAT), and polyvinylcarbazole (PVCz).

Examples of the solvent include toluene, xylene, chloroform, and the like. Examples of the dissolution or uniform dispersion method include methods such as stirring, heating and stirring, and ultrasonic dispersion.
The application method is not particularly limited, and examples thereof include an inkjet method, a spray method, a dip method, a spin coating method, a slit coating method, a transfer printing method, a roll coating method, and a brush coating method. Application is preferably performed under an inert gas such as nitrogen or argon.
Examples of the solvent evaporation method include a method of heating in an oven or a hot plate under an inert gas or in a vacuum.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated more concretely, this invention is not limited to the following Example. In addition, since the exact moisture content in the used heteropolyacid compound is unknown, the solid content concentration described below was calculated without subtracting the moisture content as it was as the weighed value. In the weighing, pretreatment such as water removal was not performed, and the purchased compound was used as it was.

[1] Preparation of charge transporting varnish and charge transporting thin film [Example 1]
270 mg of N, N, N ′, N′-tetraphenyl-pC-aminopentaaniline (hereinafter abbreviated as TPAPA) represented by the above formula (6) and phosphomolybdic acid (manufactured by Kanto Chemical Co., Inc., hereinafter) In a nitrogen atmosphere, 11.47 g of DMI, which is a good solvent, was added to and dissolved in a 540 mg mixture. To this solution, 5.73 g of propylene glycol and 17.20 g of cyclohexanol melted by heating to 40 ° C. were added and allowed to cool to room temperature to obtain a greenish black transparent solution.
The obtained solution was filtered using a PTFE filter having a pore size of 0.2 μm to obtain a greenish black transparent charge transporting varnish (solid content concentration 2.3 mass%, viscosity 11 mPa · s, 25 ° C.).
The obtained varnish was applied by spin coating on an ITO substrate that had been subjected to ozone cleaning for 30 minutes, and baked at 220 ° C. for 30 minutes in the air on a hot plate to form a charge transporting thin film. The thin film obtained was a uniform amorphous solid.
The TPAPA represented by the formula (6) was synthesized according to the method described in International Publication No. 2008/129947.

[Example 2]
To a mixture of 270 mg of N-phenyltetraaniline (hereinafter referred to as PTA) represented by the above formula (8) and 540 mg of PMA, 11.47 g of DMI which is a good solvent was added and dissolved in a nitrogen atmosphere. To this solution, 5.73 g of propylene glycol and 17.20 g of cyclohexanol melted by heating to 40 ° C. were added and allowed to cool to room temperature to obtain a greenish black transparent solution.
The obtained solution was filtered using a PTFE filter having a pore size of 0.2 μm to obtain a green-black transparent charge transporting varnish (viscosity 11 mPa · s, 25 ° C.).
The obtained varnish was applied by spin coating on an ITO substrate that had been subjected to ozone cleaning for 30 minutes, and baked at 220 ° C. for 30 minutes in the air on a hot plate to form a charge transporting thin film. The thin film obtained was a uniform amorphous solid.
In addition, PTA represented by the said Formula (8) is Bulletin of Chemical Society of Japan (1994), 67th volume, p. Synthesized according to the method described in 1749-1752.

[Example 3]
Nitrogen atmosphere for a mixture of 270 mg of oxidized N, N, N ′, N′-tetraphenyl-pC-aminotetraaniline (hereinafter abbreviated as ox-TPATA) represented by the following formula (9) and 540 mg of PMA Among them, 11.47 g of DMI which is a good solvent was added and dissolved. To this solution, 5.73 g of propylene glycol and 17.20 g of cyclohexanol melted by heating to 40 ° C. were added and allowed to cool to room temperature to obtain a greenish black transparent solution.
The obtained solution was filtered using a PTFE filter having a pore size of 0.2 μm to obtain a greenish black transparent charge transporting varnish (solid content concentration 2.3 mass%, viscosity 11 mPa · s, 25 ° C.).
The obtained varnish was applied by spin coating on an ITO substrate that had been subjected to ozone cleaning for 30 minutes, and baked at 220 ° C. for 30 minutes in the air on a hot plate to form a charge transporting thin film. The thin film obtained was a uniform amorphous solid.
In addition, ox-TPATA represented by the formula (9) was synthesized according to the methods described in International Publication No. 2008/129947 and International Publication No. 2008/01047.

[Example 4]
To a mixture of 200 mg of PTA, 204 mg of NSO-2 and 204 mg of PMA, 13.30 g of DMI as a good solvent was added and dissolved in a nitrogen atmosphere. To this solution, 6.65 g of propylene glycol and 19.95 g of cyclohexanol melted by heating to 40 ° C. were added and allowed to cool to room temperature to obtain a greenish black transparent solution.
The obtained solution was filtered using a PTFE filter having a pore size of 0.2 μm to obtain a green-black transparent charge transporting varnish (viscosity 11 mPa · s, 25 ° C.).
The obtained varnish was applied by spin coating on an ITO substrate that had been subjected to ozone cleaning for 30 minutes, and baked at 220 ° C. for 30 minutes in the air on a hot plate to form a charge transporting thin film. The thin film obtained was a uniform amorphous solid.
NSO-2 represented by the following formula was synthesized according to International Publication No. 2006/025342.

[Example 5]
To a mixture of 200 mg of TPAPA and 400 mg of PMA, 13.79 g of DMI was added and dissolved in a nitrogen atmosphere. To this solution, 19.70 g of 2,3-butanediol and 5.91 g of acetic acid-n-hexyl were added and stirred at room temperature to obtain a greenish black transparent solution.
The obtained solution was filtered using a PTFE filter having a pore size of 0.2 μm to obtain a green-black transparent charge transporting varnish (viscosity 8 mPa · s, 25 ° C.).
The obtained varnish was applied to the ITO substrate that had been subjected to ozone cleaning for 30 minutes using a spray coating apparatus (NVD200, manufactured by Fujimori Research Laboratory Co., Ltd.) by a spray coating method. A charge transporting thin film was formed by baking at 30 ° C. for 30 minutes. The thin film obtained was a uniform amorphous solid.

[Comparative Example 1]
To a mixture of 50 mg of PTA and 102 mg of NSO-2, 1.68 mL of DMI was added and dissolved in a nitrogen atmosphere. To this solution, 0.85 mL of propylene glycol and 2.78 mL of cyclohexanol melted by heating to 40 ° C. were added and allowed to cool to room temperature to obtain a green transparent solution.
The obtained solution was filtered using a PTFE filter having a pore size of 0.2 μm to obtain a green transparent charge transporting varnish (viscosity 11 mPa · s, 25 ° C.).
The obtained varnish was applied by spin coating on an ITO substrate that had been subjected to ozone cleaning for 30 minutes, and baked at 220 ° C. for 30 minutes in the air on a hot plate to form a charge transporting thin film. The thin film obtained was a uniform amorphous solid.

[Comparative Example 2]
PEDOT / PSS (manufactured by HC Starck, grade name CH8000) was applied on the ITO substrate by spin coating, and baked on the hot plate at 100 ° C. for 60 minutes in the air to form a charge transporting thin film. The thin film obtained was a uniform amorphous solid.

[Comparative Example 3]
PTA is used as a charge transporting host material, and molybdenum oxide (manufactured by Kanto Chemical Co., Ltd., MoO ₃ ), molybdic acid (manufactured by Kanto Chemical Co., Ltd., H ₂ MoO ₄ ), ammonium molybdate (as a charge transporting host material) Manufactured by Kanto Chemical Co., Inc., (NH ₄ ) ₆ Mo ₇ O ₂₄ ), tungsten oxide (manufactured by Kanto Chemical Co., Ltd., WO ₃ ), vanadium oxide (manufactured by Kanto Chemical Co., Inc., V ₂ O ₅ ), manganese oxide Although an attempt was made to prepare a charge transporting varnish using MnO ₂ (manufactured by Kanto Chemical Co., Ltd.), a homogeneous solution could not be obtained because the solubility in each of the good solvents was extremely low.

[Comparative Example 4]
To a mixture of 100 mg of PTA and 200 mg of manganese acetate (manufactured by Kanto Chemical Co., Inc., Mn (OCOCH ₃ ) ₃ ), 5.70 g of DMI was added and dissolved in a nitrogen atmosphere. Oxidation (dehydrogenation) reaction of PTA occurred, and the liquid turned black and a black solid was deposited. When PMA is used, PTA dehydrogenation reaction does not occur, so there is no solid precipitation, and it is understood that manganese acetate is inferior in the stability of the charge transporting varnish. In addition, as shown in International Publication No. 2008/01047, an oxidized form of PTA (quinone diimine form) has low solubility and is likely to cause solid precipitation, so that it contains an oxidized form in the state of charge transporting varnish and during coating. Desirably not. However, after that, it is desirable to generate an oxidant on the substrate by firing in the air from the viewpoint of improving the charge transportability. In N-phenyltrianiline and its analogs, solid precipitation hardly occurs even by oxidation (dehydrogenation), but the number is narrowed, so that it can be seen that manganese acetate has a narrow range of applicable host materials.

Table 1 shows the solid content concentration, thin film thickness, and ionization potential (Ip) of the varnishes of Examples 1 to 5 and Comparative Examples 1 and 2. In addition, Table 1 shows the refractive indexes at 450 nm and 650 nm of the thin films obtained in Examples 1 and 2.
The ionization potential was measured using a photoelectron spectrometer AC-2 manufactured by Riken Keiki Co., Ltd. The film thickness was measured using Surfcorder ET-4000A manufactured by Kosaka Laboratory. The refractive index was measured using M-2000 manufactured by JA Woollam Japan.

[2] Fabrication of OLED element [Example 6]
After forming a hole transporting thin film on the ITO substrate by the same method as in Example 4, this substrate was introduced into a vacuum deposition apparatus, and α-NPD and Alq ₃ doped with rubrene at a capacity ratio of 7%, Alq ₃ , LiF and Al were sequentially deposited to produce an OLED element (light emitting area: 4 mm ² ). The film thicknesses were 30 nm, 30 nm, 30 nm, 0.8 nm, and 150 nm, respectively, and the vapor deposition operation was performed after the pressure became 2 × 10 ⁻⁴ Pa or less. The deposition rate was 0.1 to 0.2 nm / s for α-NPD and Alq ₃ , 0.01 to 0.02 nm / s for rubrene and LiF, and 0.2 to 0.4 nm / s for Al. The transfer operation between the vapor deposition operations was performed in a vacuum.

[Comparative Example 5]
After a charge transporting thin film was formed on the ITO substrate by the same method as in Comparative Example 1, each film was deposited by the same method as in Example 6 to produce an OLED element (light emitting area: 4 mm ² ).
The characteristics of the OLED elements obtained in Example 6 and Comparative Example 5 were measured using an organic EL light emission efficiency measuring device (EL1003, manufactured by Precise Gauge Co., Ltd.). The measurement results are shown in Table 2.

  As shown in Table 2, it can be seen that the OLED characteristics obtained in Example 6 have a remarkably long half-luminance time as compared with that of Comparative Example 5 and good lifetime characteristics. It can also be seen that the current density and voltage are almost the same.

[Examples 7 to 9]
After forming a hole transporting thin film on the ITO substrate by the same method as in Examples 1 to 3, this substrate was introduced into a vacuum deposition apparatus, and α-NPD, Alq ₃ , LiF, and Al were sequentially deposited. Then, an OLED element was produced (light emitting area: 100 mm ² ). The film thicknesses were 40 nm, 60 nm, 0.8 nm, and 150 nm, respectively, and the vapor deposition operation was performed after the pressure became 2 × 10 ⁻⁴ Pa or less. The deposition rate was 0.1 to 0.2 nm / s for α-NPD and Alq ₃ , 0.01 to 0.02 nm / s for LiF, and 0.2 to 0.4 nm / s for Al. The transfer operation between the vapor deposition operations was performed in a vacuum.

[Comparative Example 6]
An OLED element was fabricated in the same manner as in Example 7 except that the hole injection layer was not provided and the film thickness of α-NPD as the hole transport layer was set to 70 nm.

[Comparative Example 7]
PEDOT / PSS (manufactured by HC Starck, grade name AI4083) was applied on the ITO substrate by a spin coating method, and baked on a hot plate at 100 ° C. for 60 minutes to form a charge transporting thin film.
An OLED element in which the hole injection layer is a PEDOT / PSS thin film was produced in the same manner as in Example 7 except that this substrate was used.
Table 3 shows the results of measuring the characteristics of the OLED elements obtained in Examples 7 to 9 and Comparative Examples 6 and 7.

As shown in Table 3, thin film constituting the hole injection layer in the device of Example 7-9 has an extremely high flatness as compared with the PEDOT / PSS film, the stability of characteristics even light-emitting area 100 mm ² There was no problem. It can be seen that the lifetime is equivalent or better in spite of a large light emitting area, and is greatly improved by combination with an appropriate host material.

[3] Conductivity measurement [Example 10]
The following experiment was conducted to conduct the conductivity measurement. A 30 mass% DMAc solution of PTA / PMA (mass ratio 1/2) was prepared as a charge transporting varnish using the same method as in Example 2 except that the solvent was changed to DMAc. In the conductivity measurement, the resistance value of the sample thin film itself needs to sufficiently exceed the resistance of the measuring element, and it is necessary to form a thick film. Therefore, a high concentration varnish was prepared.
The obtained varnish was applied by spin coating on an ITO substrate that had been subjected to ozone cleaning for 30 minutes, and baked at 220 ° C. for 30 minutes in the air on a hot plate to form a charge transporting thin film having a thickness of 360 nm. The thin film obtained was a uniform amorphous solid.

[Comparative Example 8]
PEDOT / PSS (manufactured by HC Starck, grade name CH8000) was applied on the ITO substrate by spin coating, and baked on the hot plate at 100 ° C. for 60 minutes in the air to form a charge transporting thin film. The thin film obtained was a uniform amorphous solid.
Table 4 shows the electrical conductivity of the thin films obtained in Example 10 and Comparative Example 8.
The conductivity was measured using a sandwich-type element (ITO / sample / Al (150 nm)) in which each of the obtained substrates was introduced into a vacuum deposition apparatus and Al was deposited with a thickness of 150 nm using a deposition mask ( Electrode area 0.2 mm ² , current density 100 mA / cm ² ).

As shown in Table 4, the PTA / PMA used in Example 10 has a small electric field dependency of conductivity, shows a good charge transport property at a slight voltage, and has a high conductivity sufficient as a hole injection layer material. (In general, 10 ⁻⁷ S / cm or more is necessary). Note that, in a material having a small electric field injection barrier from the electrode, the Ip value is desirably a value close to or deeper than that of the hole transport material, that is, about 5.4 eV or deeper, but the Ip value is within an appropriate range. Met.

[4] Oxidation evaluation for triarylamine-containing material [Example 11]
Currently, triarylamine-containing materials such as triphenylamine-containing materials are mostly used for the hole transport layer laminated adjacent to the hole injection layer. In order to evaluate the oxidizability of the heteropolyacid compound of the present invention to a triphenylamine-containing compound, the following experiment was conducted.
Since triphenylamine-containing compounds are similar in physical properties to other triarylamine-containing compounds used as hole transport layer materials, it is possible to evaluate the oxidation properties of triarylamine-based hole transport layer materials in general. . Having an oxidizing property with respect to the hole transport layer material means that carriers can be generated electrostatically in a part of the hole transport layer, thereby reducing the driving voltage in the organic EL element. It can be reduced.

7.05 g of DMI is added to 0.15 g of the triphenylamine dimer represented by the following formula and 0.30 g of the phosphomolybdic acid (twice that of the triphenylamine dimer in weight ratio), and the mixture is heated and stirred at 60 ° C. And dissolved, and allowed to cool to room temperature to obtain a homogeneous solution.
The obtained solution was filtered using a PTFE filter having a pore size of 0.2 μm to obtain a light brown transparent charge transporting varnish (solid content concentration 6.0 mass%).
The obtained varnish was applied by spin coating on a quartz substrate that had been subjected to ozone cleaning for 30 minutes, and baked on a hot plate at 150 ° C. for 30 minutes in the atmosphere to form a charge transporting thin film. The thin film obtained was a uniform amorphous solid. The UV-VIS spectrum of the obtained thin film was measured (measurement apparatus: UV-3100, manufactured by Shimadzu Corporation), and broad absorption peaks were generated at 550 nm and 730 nm.

These absorption peaks do not exist in the triphenylamine dimer-only thin film and the phosphomolybdic acid-only thin film, and it is considered that this absorption peak is derived from the cation or dication of the triphenylamine dimer. In addition, about the cation production | generation of a triarylamine-type material, the research using (alpha) -NPD is performed well, and in a cation, an absorption peak generate | occur | produces in 490 nm and 1330 nm, and it originates in a dication by increasing the oxidizing agent to act. It has been found that absorption peaks shift to 610 nm and 810 nm.
From the above results, it can be seen that phosphomolybdic acid has an oxidizability to triphenylamine dimer. Therefore, a hole injection layer made of phosphomolybdic acid forms a doping layer by oxidizing the contact interface with a hole transport layer made of a hole transport material containing triphenylamine or an analogous skeleton thereof. It can be seen that this can contribute to a decrease in driving voltage of the organic EL element.

[Comparative Example 9]
A charge transporting thin film was formed in the same manner except that the phosphomolybdic acid in Example 5 was changed to dinonylnaphthalenedisulfonic acid (manufactured by Aldrich). When the UV-VIS spectrum of the obtained thin film was measured, no new absorption peak other than the absorption peak obtained in each single film was generated. It can be seen that 5-sulfosaticylic acid does not have oxidizability for triphenylamine dimer.

Claims (4)

  An electron-accepting dopant for an organic electroluminescence device, comprising a heteropolyacid compound.   The electron-accepting dopant according to claim 1, wherein the heteropolyacid compound is phosphomolybdic acid, silicomolybdic acid, phosphotungstic acid, phosphotungstomolybdic acid or silicotungstic acid.   The electron-accepting dopant according to claim 1 or 2, which is used for a hole injection layer or a hole transport layer of an organic electroluminescence element.   The electron-accepting dopant according to claim 3, which is used for a hole injection layer of an organic electroluminescence element.