JP2006114544A - Organic electroluminescence device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic EL element provided with a hole injection layer contributing to high luminous efficiency, low driving voltage, long life, etc. of the organic EL element.
An organic electroluminescent device having a light emitting layer and a hole transport layer disposed between at least a pair of electrodes, and at least one hole injection layer between the hole transport layer and an anode, An organic EL element using an acceptor compound as a hole injection layer.
[Selection figure] None

Description

  The present invention relates to an organic electroluminescent device (hereinafter abbreviated as an organic EL device) using a novel hole injection layer.

  In recent years, organic EL elements have attracted attention as next-generation full-color flat panel displays and are increasingly being installed in mobile phones and the like. For this reason, many attempts have been made to improve characteristics such as low voltage, high efficiency, and long life. In general, in an organic EL element, a hole injection layer, a hole transport layer, a light emitting layer, and an electron injection layer made of an organic compound are sandwiched between an anode and a cathode. For the hole injection layer, a starburst amine compound (see Patent Document 1), an oligoamine compound (see Patent Document 2) or copper phthalocyanine (see Patent Document 3) has been used. In the polymer system, PEDOT / PSS or an amine polymer (see Patent Document 4) has been used. Other than this, recently, an example in which an organic compound having p-type semiconductor properties is used for a hole transport layer has been reported (see Patent Document 5). However, the market demand for recent flat panel displays is increasing, and further improvements in luminous efficiency, lower power consumption, longer life, and the like have been demanded of organic EL elements.

  In order to obtain organic EL devices with high luminous efficiency, low power consumption, and long life, the role of the hole injection layer is large. For low power consumption, it is necessary to increase the conductivity, and for the long life, the anode surface Therefore, it is necessary to suppress the roughness and smoothen the surface. However, in order to improve the smoothness, there is a countermeasure such as increasing the thickness of the hole injection layer, but it tends to lead to a decrease in luminous efficiency and an increase in power consumption, and it is difficult to maintain both characteristics. .

  For the purpose of providing an EL device having a high hole injection efficiency and a high light emission efficiency and a low driving voltage, an electron accepting substance having an electron affinity of 1.15 eV or more, and thermal energy and / or light irradiation at room temperature, An organic EL element provided with a hole injection control promoting layer containing at least a charge generating agent for generating carriers (see Patent Document 6) has been reported. However, there has been a problem that a charge generating agent that tends to adversely affect the lifetime has to be used.

  In addition, an element in which an electron-accepting compound is contained in a hole injection layer in order to oxidize a hole transport material having a molecular weight of less than 1000 (see Patent Document 7) has been reported. However, there is a problem that the element manufacturing method is limited to a wet process, and a practically important driving life is not described, and it cannot be said that the technique is effective.

Japanese Patent Laid-Open No. 04-308688 Japanese Patent Laid-Open No. 08-193191 JP-A-57-51781 JP 2000-340363 A Special table 2003-519432 gazette JP 2000-286054 A JP 2002-56985 A

  The present invention has been made in view of the problems of such conventional techniques. An object of the present invention is to provide an organic EL device having a hole injection layer that contributes to high light emission efficiency, low driving voltage, long life, etc. of the organic EL device.

  As a result of intensive studies, the present inventors have found that by using an acceptor compound for the hole injection layer of an organic EL element, an organic EL element that can be driven with high luminous efficiency, low power consumption, and long life is obtained. Based on this finding, the present invention has been completed.

  The acceptor compound used in the present invention is a compound containing an electron-withdrawing group such as a cyano group or a nitro group. Preferably, it is a compound that is not detected when the ionization potential measured by photoelectron spectroscopy is 5.7 eV or less.

Said subject is solved by each item shown below.
[1] An organic electroluminescent device having a light emitting layer and a hole transport layer disposed between at least a pair of electrodes, and at least one hole injection layer between the hole transport layer and an anode, An organic EL device using an acceptor compound as an injection layer.

[2] The organic EL device according to item [1], wherein the acceptor compound is a compound that is not detected when the ionization potential measured by photoelectron spectroscopy is 5.7 eV or less.

[3] In an organic EL device having a light emitting layer, a hole transport layer, and a hole injection layer disposed between at least a pair of electrodes, the hole transport layer is made of at least one arylamine compound [1] or [ [2] The organic EL device according to item.

[4] The organic EL device according to any one of [1] to [3], wherein the compound that can be used as the hole injection layer is at least one compound represented by the formula (1).

Ar ¹ (CN) n (1)

Here, Ar ¹ is a substituted or unsubstituted aromatic group or a substituted or unsubstituted condensed polycyclic hydrocarbon group, and n is an integer of 1 to 10.

[5] The organic EL device according to item [4], wherein in formula (1), Ar ¹ is a naphthalene ring group and n is an integer of 1 to 8.

[6] The organic EL device according to item [4], wherein Ar ¹ in formula (1) is an anthracene ring group.

[7] The organic EL device according to item [4], wherein Ar ¹ in formula (1) is a phenanthrene ring group.

[8] The organic EL device according to item [4], wherein Ar ¹ in formula (1) is a pyrene ring group.

[9] The organic EL device according to item [4], wherein Ar ¹ in formula (1) is a perylene ring group.

[10] The organic EL device according to item [4], wherein in formula (1), Ar ¹ is a triphenylene ring group.

[11] The organic EL device according to any one of [1] to [3], wherein the compound that can be used as the hole injection layer is at least one compound represented by the formula (2).

Ar ² (CN) n (2)

Here, Ar ² is a substituted or unsubstituted nitrogen-free aromatic heterocycle, and n is an integer of 1 to 10.

[12] The organic EL device according to any one of [1] to [3], wherein the compound that can be used as the hole injection layer is at least one compound represented by the formula (3).

Ar ³ (CN) n (3)

Here, Ar ³ is a substituted or unsubstituted aromatic heterocyclic group containing 5 or less nitrogen atoms, and n is an integer of 1 to 10.

[13] The organic EL device according to any one of [1] to [3], wherein the compound that can be used as the hole injection layer is at least one compound represented by the formula (4).

Ar ⁴ (= C (CN) ₂ ) n (4)

Here, Ar ⁴ is a substituted or unsubstituted aromatic group or a substituted or unsubstituted condensed polycyclic hydrocarbon group, and n is an integer of 1 to 5.

[14] The organic EL device according to item [13], wherein in formula (4), Ar ⁴ is a naphthalene ring group or an anthracene ring group, and n is 2.

  In the organic EL device using the hole injection layer of the present invention, considering that the material used for the known hole injection layer has a donor property, the hole injection layer of the present application has an acceptor property. The mechanism of charge injection and transport is considered to be different. This difference in mechanism is considered to contribute to the fact that the device can be driven at a low voltage and that the continuous driving life is long. By using the organic EL element of the present invention, a display device with high luminous efficiency such as full color display, low driving voltage and long life can be produced.

Hereinafter, the acceptor compound used in the present invention will be described in more detail.
The first of the acceptor compounds used in the present invention is a compound having a cyano group represented by the formula (1).

Ar ¹ (CN) n (1)

In formula (1), Ar ¹ is a substituted or unsubstituted aromatic group or a substituted or unsubstituted condensed polycyclic hydrocarbon group. Examples of this aromatic group or condensed polycyclic hydrocarbon group are benzene ring, naphthalene ring, anthracene ring, phenanthrene ring, pyrene ring, triphenylene ring, perylene ring, tetracene ring, pentacene ring, chrysene ring, coronene ring, picene ring. A ring-based group. n is an integer of 1-10.

  The substituent in the aromatic group or the condensed polycyclic hydrocarbon group is an aromatic group, a condensed hydrocarbon group, a heterocyclic group, an alkyl group, a substituted boryl group, a substituted or unsubstituted carbonyl group. -CO-R, unsubstituted means -CO-H, where R is an organic group), substituted or unsubstituted carboxyl group (where substituted is -CO-OR) Yes, unsubstituted means -CO-OH.) Or a substituted silyl group.

  Preferred examples of the substituent are phenyl, pyridyl, silole, methyl, bis (trimethylphenyl) boryl, benzoyl, phenyloxycarbonyl and triphenylsilyl. Also preferred are fused ring groups such as benzofused.

The second of the acceptor compounds used in the present invention is a compound having a cyano group represented by the formula (2).

Ar ² (CN) n (2)

In formula (2), Ar ² is a substituted or unsubstituted nitrogen-free aromatic heterocyclic group. Examples of the nitrogen-free aromatic heterocyclic group include a thiophene ring group, a furan ring group, and a silole ring group. Preferred examples of the substituent in the nitrogen-free aromatic heterocyclic group are the same as described above.

The 3rd of the acceptor property compounds used by this invention is a compound which has a cyano group represented by Formula (3).

Ar ³ (CN) n (3)

In the formula (3), Ar ³ is a substituted or unsubstituted aromatic heterocyclic group containing 5 or less nitrogen atoms. Examples of this aromatic heterocyclic ring containing 5 or less nitrogen atoms are pyridine, pyrimidine, pyrazine, imidazole, thiazole, oxazole, oxadiazole and the like. Preferable examples of the substituent in the aromatic heterocyclic group containing 5 or less nitrogen atoms are the same as described above.

The fourth of the acceptor compounds used in the present invention is an organic EL device using a compound having a dicyanomethylene group represented by formula (4) for the hole injection layer.

Ar ⁴ (= C (CN) ₂ ) n (4)

Here, Ar ⁴ is a substituted or unsubstituted aromatic group or a substituted or unsubstituted condensed polycyclic hydrocarbon group, and n is an integer of 1 to 5. Examples of the aromatic group or the condensed polycyclic hydrocarbon group include a benzene ring group, a naphthalene ring group, and an anthracene ring group. Preferred examples of the substituent in this aromatic group or condensed polycyclic hydrocarbon group are the same as described above. A preferred example of n is 1 or 2.

  Examples of materials used for the hole injection layer of the present invention are compounds of the following formulas (5) to (18), but the present invention is not limited by disclosure of these specific structures.

  The material used for the hole injection layer of the present invention can be synthesized using a known synthesis method. For example, a cyano compound can be synthesized by a method of directly cyanating from a corresponding halide. A dicyanomethylene compound can be synthesized by reacting a corresponding quinone and malononitrile in the presence of a base.

  The hole injection layer of the present invention is characterized by being made of an acceptor material, and contributes to lowering the voltage and extending the life of the organic EL element. In addition, since the acceptor material can have a structure with high planarity, the charge mobility can be increased. As a result, the emission color due to optical interference of the organic EL element, the efficiency of taking out the emission to the outside can be increased. Alternatively, it is advantageous in optimizing optical characteristics such as the angle dependency of the emission intensity.

  The structure of the organic EL device of the present invention has various modes, but is basically a multilayer structure in which at least a hole injection layer, a hole transport layer, and a light emitting layer are sandwiched between an anode and a cathode. Examples of the specific configuration of the element are (1) anode / hole injection layer / hole transport layer / light emitting layer / cathode, and (2) anode / hole injection layer / hole transport layer / light emitting layer / electron transport. Layer / cathode, (3) anode / hole injection layer / hole transport layer / light emitting layer / electron transport layer / electron injection layer / cathode, etc.

  Since the hole injection layer of the present invention has high charge injection properties and charge transport properties, it can be used effectively for organic EL devices. In the organic EL device of the present invention, by combining the hole injection layer and the hole transport layer, the light emission efficiency can be increased, the driving voltage can be lowered, or the life can be extended.

  The light-emitting material or light-emitting dopant that can be used in the light-emitting layer of the organic EL device of the present invention is as described in the edited by the Society of Polymer Science, Japan, “Functional Functional Materials”, Joint Publication (1991), P236. Luminescent materials such as daylight fluorescent materials, fluorescent brighteners, laser dyes, organic scintillators, various fluorescent analysis reagents, etc., supervised by Keiji Koji, “Organic EL materials and displays” published by CMC Publishing Co. (2001) P155-156. And a light emitting material of a triplet material as described in P170-172 of the same.

  Other luminescent materials or compounds that can be used as luminescent dopants include polycyclic aromatic compounds, heteroaromatic compounds, organometallic complexes, dyes, polymer-based luminescent materials, coumarin derivatives, borane derivatives, oxazine derivatives, and spiro rings. Compounds, oxadiazole derivatives, fluorene derivatives, and the like. Examples of the polycyclic aromatic compound are anthracene derivatives, phenanthrene derivatives, naphthacene derivatives, pyrene derivatives, chrysene derivatives, perylene derivatives, coronene derivatives, rubrene derivatives, and the like. Examples of heteroaromatic compounds include oxadiazole derivatives, pyrazoloquinoline derivatives, pyridine derivatives, pyran derivatives, phenanthroline derivatives, silole derivatives, thiophene derivatives having a triphenylamino group, quinacridone derivatives having a dialkylamino group or a diarylamino group Etc. Examples of organometallic complexes are zinc, aluminum, beryllium, europium, terbium, dysprosium, iridium, platinum, etc., quinolinol derivatives, benzoxazole derivatives, benzothiazole derivatives, oxadiazole derivatives, thiadiazole derivatives, phenylpyridine derivatives, phenyl A complex with a benzimidazole derivative, a pyrrole derivative, a pyridine derivative, a phenanthroline derivative, or the like. Examples of dyes are xanthene derivatives, polymethine derivatives, porphyrin derivatives, coumarin derivatives, dicyanomethylenepyran derivatives, dicyanomethylenethiopyran derivatives, oxobenzanthracene derivatives, carbostyril derivatives, perylene derivatives, benzoxazole derivatives, benzothiazole derivatives, benzimidazoles And pigments such as derivatives. Examples of the polymeric light-emitting material are polyparaphenyl vinylene derivatives, polyalkylthiophene derivatives, polydialkylfluorene derivatives, polyparaphenylene derivatives, and the like.

  In particular, the luminescent dopant is preferably a styrylamine derivative, a perylene derivative, a borane derivative, a coumarin derivative, a pyran derivative, an iridium complex, or a platinum complex. Examples of perylene derivatives are 3,10-di (2,6-dimethylphenyl) perylene, 3,10-di (2,4,6-trimethylphenyl) perylene, 3,10-diphenylperylene, 3,4-diphenyl Perylene, 2,5,8,11-tetra-t-butylperylene, 3,4,9,10-tetraphenylperylene, 3- (1′-pyrenyl) -8,11-di (t-butyl) perylene, 3- (9′-anthryl) -8,11-di (t-butyl) perylene, 3,3′-bis (8,11-di (t-butyl) perylenyl) and the like. Examples of borane derivatives are 1,8-diphenyl-10- (dimesitylboryl) anthracene, 9-phenyl-10- (dimesitylboryl) anthracene, 4- (9′-anthryl) dimesitylborylnaphthalene, 4- (10′- Phenyl-9'-anthryl) dimesitylborylnaphthalene, 9- (dimesitylboryl) anthracene, 9- (4'-biphenyl) -10- (dimesitylboryl) anthracene, 9- (4 '-(N-carbazolyl) phenyl)- 10- (dimesitylboryl) anthracene and the like. Examples of coumarin derivatives are coumarin-6, coumarin-334 and the like.

Examples of pyran derivatives are the following DCM, DCJTB, and the like.

Examples of the iridium complex include Ir (ppy) _{3 described} below.

Examples of the platinum complex include the following PtOEP.

  The amount of dopant used varies depending on the dopant and may be determined according to the characteristics of the dopant. The standard of the amount of the dopant used is 0.001 to 50% by weight, preferably 0.1 to 20% by weight, based on the entire light emitting material.

  The electron transport material and electron injection material used in the organic EL device of the present invention can be selected from compounds that can be used as an electron transfer compound in a photoconductive material and compounds that can be used in an electron injection layer and an electron transport layer of an organic EL device. Can be selected and used.

  Examples of such electron transfer compounds are metal complexes of quinolinol metal complexes, pyridine derivatives, phenanthroline derivatives, quinone derivatives, dicyanomethylene derivatives, perylene derivatives, oxadiazole derivatives, thiophene derivatives, triazole derivatives, thiadiazole derivatives, oxine derivatives. Quinoxaline derivatives, quinoxaline derivative polymers, benzazole compounds, gallium complexes, pyrazole derivatives, perfluorinated phenylene derivatives, triazine derivatives, pyrazine derivatives, benzoquinoline derivatives, imidazopyridine derivatives, nitrogen-containing heterocyclic derivatives, borane derivatives, etc. is there.

  Preferred examples of the electron transfer compound are quinolinol metal complexes, pyridine derivatives or phenanthroline derivatives. Examples of quinolinol-based metal complexes are tris (8-hydroxyquinoline) aluminum (hereinafter abbreviated as ALQ), bis (10-hydroxybenzo [h] quinoline) beryllium, tris (4-methyl-8-hydroxyquinoline). Aluminum, bis (2-methyl-8-hydroxyquinoline)-(4-phenylphenol) aluminum and the like. Examples of pyridine derivatives are 2,5-bis (6 ′-(2 ′, 2 ″ -bipyridyl) -1,1-dimethyl-3,4-diphenylsilole (hereinafter abbreviated as PyPySPyPy), 9,10− Di (2 ′, 2 ″ -bipyridyl) anthracene, 2,5-di (2 ′, 2 ″ -bipyridyl) thiophene, 2,5-di (3 ′, 2 ″ -bipyridyl) thiophene, 6′6 ″ -di (2-pyridyl) 2,2 ′: 4 ′, 3 ″: 2 ″, 2 ′ ″-quaterpyridine, etc. Examples of phenanthroline derivatives are 4,7-diphenyl-1,10-phenanthroline, 2, 9-dimethyl-4,7-diphenyl-1,10-phenanthroline, 9,10-di (1,10-phenanthroline-2-yl) anthracene, 2,6-di (1,10-phenanthroline-5-yl) Pyridine, 1, , 5-tri (5-1,10-phenanthroline-yl) benzene, 9,9'-difluoro - bis (1,10-phenanthroline-5-yl) and the like.

  Regarding the hole transport material used in the organic EL device of the present invention, in the photoconductive material, a compound conventionally used as a charge transport material for holes, the hole injection layer of the organic EL device, and the hole transport. It can be arbitrarily selected from known materials used for the layer. Examples thereof are carbazole derivatives, triarylamine derivatives and the like. Examples of the carbazole derivative are N-phenylcarbazole, polyvinylcarbazole and the like. Examples of triarylamine derivatives are polymers having an aromatic tertiary amine in the main chain or side chain, 1,1-bis (4-di-p-tolylaminophenyl) cyclohexane, N, N′-diphenyl-N , N′-di (3-methylphenyl) -4,4′-diaminobiphenyl, N, N′-diphenyl-N, N′-dinaphthyl-4,4′-diaminobiphenyl (hereinafter abbreviated as NPD) 4,4 ′, 4 ″ -tris {N- (3-methylphenyl) -N-phenylamino} triphenylamine, starburstamine derivatives, etc., preferably triaryls that do not have large absorption in the visible region It is an amine derivative.

Each layer constituting the organic EL device of the present invention can be formed by forming a material to constitute each layer into a thin film by a method such as a vapor deposition method, a printing method, a spin coating method, or a casting method. The thickness of each layer formed in this way is not particularly limited and can be appropriately set according to the properties of the material, but is usually in the range of 2 nm to 5000 nm. When a thin film is formed using a vapor deposition method, the vapor deposition conditions vary depending on the type of material, the intended crystal structure and association structure of the film, and the like. Deposition conditions generally include a boat heating temperature of 50 to 400 ° C., a degree of vacuum of 10 ⁻⁶ to 10 ⁻³ Pa, a deposition rate of 0.01 to 50 nm / second, a substrate temperature of −150 to + 300 ° C., and a film thickness of 5 nm to 5 μm. It is preferable to set appropriately within the range.

The organic EL device of the present invention is preferably supported by a substrate in any of the structures described above. The substrate only needs to have mechanical strength, thermal stability, and transparency, and glass, a transparent plastic film, and the like can be used. As the anode material, metals, alloys, electrically conductive compounds and mixtures thereof having a work function larger than 4 eV can be used. Examples thereof are metals such as Au, CuI, indium tin oxide (hereinafter abbreviated as ITO), SnO ₂ , ZnO, and the like.

  Cathode materials can use metals, alloys, electrically conductive compounds, and mixtures thereof with work functions of less than 4 eV. Examples thereof are aluminum, calcium, magnesium, lithium, magnesium alloy, aluminum alloy and the like. Furthermore, it is possible to insert a very thin film of an insulating interface layer material such as lithium fluoride, cesium fluoride, or lithium oxide between the cathode and the organic layer. Examples are aluminum / lithium fluoride, aluminum / lithium, magnesium / silver, magnesium / indium and the like. In order to efficiently extract light emitted from the organic EL element, it is desirable that at least one of the electrodes has a light transmittance of 10% or more. The sheet resistance as the electrode is preferably several hundred Ω / □ or less. Although the film thickness depends on the properties of the electrode material, it is usually set in the range of 10 nm to 1 μm, preferably 10 to 400 nm. Such an electrode can be produced by forming a thin film by a method such as vapor deposition or sputtering using the electrode material described above.

  Next, as an example of a method for producing an organic EL device using the hole transport layer of the present invention, an organic EL composed of the above-mentioned anode / hole injection layer / hole transport layer / light emitting layer / electron transport layer / cathode. A method for creating an element will be described. A thin film of the acceptor material is formed by vapor deposition on a substrate on which the ITO electrode is patterned to form a hole injection layer, and then a thin film of a hole transport layer is formed thereon. Further, a host material and a dopant material of a light emitting material are co-deposited thereon to form a thin film to form a light emitting layer, and an electron transport layer is similarly formed on the light emitting layer by vapor deposition, and further comprises a cathode material. The target organic EL element is obtained by forming a thin film by a vapor deposition method to be a cathode. In the production of the organic EL element described above, the production order can be reversed, and the cathode, the electron transport layer, the light emitting layer, the hole transport layer, the hole injection layer, and the anode can be produced in this order.

  When a DC voltage is applied to the organic EL device thus obtained, the anode may be applied with a positive polarity and the cathode with a negative polarity. When a voltage of about 2 to 40 V is applied, a transparent or translucent electrode is applied. Luminescence can be observed from the side (anode or cathode and both). The organic EL element also emits light when an alternating voltage is applied. The alternating current waveform to be applied may be arbitrary.

The present invention will be described in more detail based on examples.
Measurement of ionization potential value It measured by photoelectron spectroscopy under atmospheric pressure using AC-1 (made by Riken Keiki Co., Ltd.). In addition, this apparatus can quantitatively measure the ionization potential value of less than 6.2 eV, and if it exceeds that, it is judged that it is 6.2 eV or more in all cases.

[Synthesis Example 1] Compound (13) Synthesis of 11,11,12,12-tetracyanoanthraquinodimethane 5.3 g of anthraquinone, 4.6 g of malononitrile, and 160 ml of dichloromethane were placed in a flask and cooled to 4 ° C. in a nitrogen atmosphere. Then, 25 g of titanium tetrachloride and 44 ml of pyridine were added dropwise. The mixture was stirred at room temperature for 12 hours, pure water and chloroform were added, the inorganic salt was filtered off, and the organic layer was extracted. The organic layer was dried, concentrated with an evaporator, and purified by recrystallization to obtain 4.1 g of 11,11,12,12-tetracyanoanthraquinodimethane.
¹ H-NMR: δ 7.44 (4H, m), δ 8.26 (4H, m)
Visible ultraviolet maximum absorption wavelength (acetonitrile solution): 281, 302, 341 (nm)

[Example 1]
A 25 mm × 75 mm × 1.1 mm glass substrate (manufactured by Tokyo Sanyo Vacuum Co., Ltd.) on which ITO was deposited to a thickness of 150 nm was used as a transparent support substrate. This transparent support substrate was fixed to a substrate holder of a commercially available vapor deposition apparatus (manufactured by Vacuum Kiko Co., Ltd.), and a molybdenum vapor deposition boat containing compound (12) (ionization potential value of 6.2 eV or more), NPD was added. A molybdenum vapor deposition boat, a molybdenum vapor deposition boat containing ALQ, a molybdenum vapor deposition boat containing lithium fluoride, and a tungsten vapor deposition boat containing aluminum were mounted. Depressurize the vacuum chamber to 1 × 10 ⁻³ Pa, heat the vapor deposition boat containing the compound (12), deposit to a thickness of 20 nm to form a hole injection layer, and then enter NPD The evaporation boat was heated and NPD was evaporated to a film thickness of 30 nm to form a hole transport layer. Next, the evaporation boat containing ALQ was heated, and ALQ was evaporated to a film thickness of 50 nm to form an electron transporting light emitting layer. The above deposition rate was 0.1 to 0.2 nm / second. Thereafter, the vapor deposition boat containing lithium fluoride is heated to deposit at a deposition rate of 0.003 to 0.01 nm / second so as to have a film thickness of 0.5 nm, and then the vapor deposition boat containing aluminum is heated. Then, an organic EL element was obtained by vapor deposition at a vapor deposition rate of 0.2 to 0.5 nm / second so as to have a film thickness of 100 nm. When a direct current voltage of about 3.5 V was applied using the ITO electrode as the anode and the lithium fluoride / aluminum electrode as the cathode, a current of about 10 mA / cm ² flowed and light emission was obtained. Further, when a constant current drive of 80 mA / cm ² was performed, the luminance half-life showed a life characteristic of 121 hours.

[Comparative Example 1]
An organic EL device was produced by the method according to Example 1 except that the compound (12) used in Example 1 was not used and the NPD film thickness was changed to 50 nm. When a direct current voltage of about 3.5 V was applied using the ITO electrode as the anode and the lithium fluoride / aluminum electrode as the cathode, a current of about 3 mA / cm ² flowed and light emission was obtained. Further, when constant current driving at 50 mA / cm ² was performed, the luminance half-life showed a life characteristic of 30 hours.

[Comparative Example 2]
An organic EL device was produced by the method according to Example 1 except that the compound (12) used in Example 1 was replaced with copper phthalocyanine (ionization potential value 5.0 eV). When a direct current voltage of about 5.6 V was applied using the ITO electrode as the anode and the lithium fluoride / aluminum electrode as the cathode, a current of about 3 mA / cm ² flowed and light emission was obtained. Further, when a constant current drive of 50 mA / cm ² was performed, the luminance half-life showed a lifetime characteristic of 100 hours.

[Comparative Example 3]
The compound (12) used in Example 1 was replaced with m-MTDATA (ionization potential value 5.1 eV), which is a compound represented by the following formula, which is a starburst amine, and was organically produced in the same manner as in Example 1. An EL element was prepared. When a direct current voltage of about 4.2 V was applied using the ITO electrode as the anode and the lithium fluoride / aluminum electrode as the cathode, a current of about 3 mA / cm ² flowed and light emission was obtained. When a constant current drive of 50 mA / cm ² was performed, the luminance half-life showed a life characteristic of 80 hours.

[Example 2]
An organic EL device was produced by the method according to Example 1 except that the compound (12) used in Example 1 was replaced with the compound (13) (ionization potential value of 6.2 eV or more). When a direct current voltage of about 3.5 V was applied using the ITO electrode as the anode and the lithium fluoride / aluminum electrode as the cathode, a current of about 3 mA / cm ² flowed and light emission was obtained. In addition, when a constant current drive of 50 mA / cm ² was performed, the luminance half time showed a life characteristic of 130 hours.

Claims (14)

An organic electroluminescent device having a light emitting layer and a hole transport layer disposed between at least a pair of electrodes, and at least one hole injection layer between the hole transport layer and an anode, wherein the hole injection layer An organic electroluminescent device characterized by using an acceptor compound. The organic electroluminescent device according to claim 1, wherein the acceptor compound is a compound that is not detected when the value of ionization potential measured by photoelectron spectroscopy is 5.7 eV or less. The organic EL device having a light emitting layer, a hole transport layer, and a hole injection layer disposed between at least a pair of electrodes, wherein the hole transport layer is made of at least one arylamine compound. Organic electroluminescent device. The organic electroluminescent element according to any one of claims 1 to 3, wherein the compound that can be used as the hole injection layer is at least one compound represented by the formula (1).

Ar ¹ (CN) n (1)

Here, Ar ¹ is a substituted or unsubstituted aromatic group or a substituted or unsubstituted condensed polycyclic hydrocarbon group, and n is an integer of 1 to 10. The organic electroluminescent element according to claim 4, wherein Ar ¹ is a naphthalene ring group and n is an integer of 1 to 8 in formula (1). The organic electroluminescent element according to claim 4, wherein Ar ¹ in formula (1) is an anthracene ring group. The organic electroluminescent element of Claim 4 whose Ar < ¹ > is a phenanthrene ring group in Formula (1). The organic electroluminescent element according to claim 4, wherein Ar ¹ in formula (1) is a pyrene ring group. The organic electroluminescent element according to claim 4, wherein Ar ¹ in formula (1) is a perylene ring group. The organic electroluminescent element according to claim 4, wherein Ar ¹ in formula (1) is a triphenylene ring group. The organic electroluminescent element according to any one of claims 1 to 3, wherein the compound that can be used as the hole injection layer is at least one compound represented by the formula (2).

Ar ² (CN) n (2)

Here, Ar ² is a substituted or unsubstituted nitrogen-free aromatic heterocyclic group, and n is an integer of 1 to 10. The organic electroluminescent element according to any one of claims 1 to 3, wherein the compound that can be used as the hole injection layer is at least one compound represented by the formula (3).

Ar ³ (CN) n (3)

Here, Ar ³ is a substituted or unsubstituted aromatic heterocyclic group containing 5 or less nitrogen atoms, and n is an integer of 1 to 10. The organic electroluminescent element according to any one of claims 1 to 3, wherein the compound that can be used as the hole injection layer is at least one compound represented by the formula (4).

Ar ⁴ (= C (CN) ₂ ) n (4)

Here, Ar ⁴ is a substituted or unsubstituted aromatic group or a substituted or unsubstituted condensed polycyclic hydrocarbon group, and n is an integer of 1 to 5. The organic electroluminescent element according to claim 13, wherein in formula (4), Ar ⁴ is a naphthalene ring group or an anthracene ring group, and n is 2.