JP2002124390A - Organic electroluminescence element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic electroluminescence element that has low starting voltage of luminance, high luminous efficiency and is superior in durability. SOLUTION: The electroluminescence element is equipped with a positive hole transporting layer that contains a copolymer, made of a structure unit (A) 5-95 mol% as expressed in Formula (1) and a structural unit (B) 5-95 mol% originated from a specific carbazole derivative.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic electroluminescence device.

[0002]

2. Description of the Related Art In recent years, organic materials have begun to be used as a hole transporting material and an electron transporting material constituting an electroluminescent device. An organic electroluminescent device using such an organic material (hereinafter referred to as "organic EL device") has been developed.
Also called an "element." ) Is being actively researched. An organic material constituting such an organic EL element is required to have excellent durability and to obtain high luminous efficiency.

Conventionally, organic materials having a hole transporting property include diamine derivatives, N, N'-diphenyl-N,
Low molecular weight organic materials such as arylamine-based compounds such as N'-di (3-methylphenyl) -4,4'-diaminobiphenyl (hereinafter also referred to as "m-TPD"), and high molecular weight organic materials such as polyvinylcarbazole Materials are known. However, since the above-mentioned low-molecular organic material has poor physical or thermal durability, when the hole transport layer is formed by the low-molecular organic material, the organic EL element is driven or stored. There is a disadvantage in that the hole transport layer is deteriorated. In addition, since a high molecular weight organic material such as polyvinyl carbazole has a very high glass transition point (Tg), a hole transport layer having excellent durability, that is, a long service life can be obtained. And the luminous efficiency is low due to insufficient hole transport performance, which poses a practical problem.

[0004]

DISCLOSURE OF THE INVENTION The present invention has been made based on the above circumstances, and its object is to provide:
An object of the present invention is to provide an organic electroluminescence device having a low light emission starting voltage, high light emission efficiency, and excellent durability.

[0005]

The organic electroluminescent device of the present invention comprises a structural unit (A) represented by the following general formula (1) and a structural unit (B) represented by the following general formula (2). And a hole transport layer containing a copolymer having a molar ratio of the structural unit (A) to the structural unit (B) of 5:95 to 95: 5. It is characterized by the following.

[0006]

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[0007]

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[0008] In the organic electroluminescence device of the present invention, the hole transport layer has a molar ratio of the structural unit (A) to the structural unit (B) of 20: 80-8.
It is preferable to contain a copolymer having a ratio of 0:20. Further, the organic electroluminescence device of the present invention preferably has at least an anode layer, the hole transport layer, a light emitting layer, and a cathode layer.

[0009]

Embodiments of the present invention will be described below in detail. FIG. 1 is an explanatory cross-sectional view showing the configuration of the organic electroluminescence element according to the first embodiment of the present invention. In this organic EL device, an anode layer (hole injection electrode layer) 2 is provided on a transparent substrate 1, a hole transport layer 10 is provided on the anode layer 2,
A light emitting layer 15 is provided on the hole transport layer 10, and a cathode layer (electron injection electrode layer) 3 is provided on the light emitting layer 15. The anode layer 2 and the cathode layer 3 are connected to a DC power supply 5.

As the transparent substrate 1, a glass substrate, a transparent resin substrate, a quartz glass substrate or the like can be used.
The anode layer 2 is made of a material having a large work function (for example, 4 eV or more), for example, an ITO film, tin oxide (S
nO ₂ ) film, copper oxide (CuO) film, zinc oxide (ZnO)
A film or the like can be used. The hole transport layer 10 is formed of a copolymer (hereinafter, referred to as “specified”) comprising a structural unit (A) represented by the general formula (1) and a structural unit (B) represented by the general formula (2). Of copolymers ”).).

<Structural Unit (A)> In the general formula (1) representing the structural unit (A), R ¹ is a hydrogen atom, an alkyl group,
Indicates an aryl group. Here, examples of the alkyl group include an alkyl group having 1 to 2 carbon atoms such as a methyl group and an ethyl group. Examples of the aryl group include a phenyl group. In the general formula (1), R ¹ is preferably a hydrogen atom or a methyl group from the viewpoint of obtaining high polymerization reactivity.

In addition, R ² , R ³ ,
R ⁴ and R ⁵ represent a hydrogen atom, an alkyl group, an aryl group, an alkoxy group, or an amino group, all of which may be the same or a part or all thereof may be different. Here, the alkyl group is not particularly limited, but may be a methyl group, an ethyl group, a propyl group,
Butyl group, hexyl group, octyl group etc.
8 alkyl groups are preferred. In particular, a methyl group is preferable in terms of obtaining higher hole transport performance, and an alkyl group having a large number of carbon atoms (for example, having 8 carbon atoms) is preferable in terms of obtaining high solubility in an organic solvent. The alkoxy group is not particularly limited, but is preferably an alkoxy group having 1 to 8 carbon atoms, such as a methoxy group, an ethoxy group, a propoxy group, and a butoxy group. Particularly, higher hole transport performance is obtained. In terms of this, a methoxy group is preferred. Examples of the aryl group include a phenyl group and a tolyl group. Examples of the amino group include, but are not particularly limited to, diphenylamino groups, diarylamino groups such as ditolylamino groups, and dimethylamino groups, diethylamino groups, and dipropylamino groups having 1 to 1 carbon atoms.
A dialkylamino group having an alkyl group of 8 is preferable, and a di-n-propylamino group and a di-i-propylamino group are particularly preferable in that higher hole transport performance is obtained.

[0013] In the general formula (1), R ² is a hydrogen atom, R ³ is an alkyl group, R ²
And R ³ are hydrogen atoms, and R ⁴ and R 3
The combination of ^5, either one of them is a hydrogen atom and the other is an alkyl group, as R ⁴ and R ⁵ are an alkyl group is preferred. Also, R ² ~
When each of R ⁵ is other than a hydrogen atom, the position is preferably a meta position or a para position.

In the general formula (1), X ¹ represents a group represented by the following formula (a) or a group represented by the following formula (b). Groups are preferred. The number m of repetitions is 0 or 1.

[0015]

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In the general formula (1), Z represents an oxycarbonyl group (—COO—), a group represented by —CONH— or a group represented by —CONHCO—. A carbonyl group and a group represented by -CONH- are preferable. The number of repetitions n is 0 or 1. ^{_{Further, -CH 2 -CR 1 - (X}} 1) m - (Z) n
The group represented by-is preferably located at the meta or para position, particularly preferably at the para position.

Preferred specific examples of the structural unit (A) represented by the general formula (1) include a structural unit represented by the following formula (a), a structural unit represented by the following formula (b), and a structural unit represented by the following formula: (C)
And the structural unit represented by the formula (b) and the structural unit represented by the formula (c) are particularly preferable.

[0018]

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[0019]

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<Structural Unit (B)> In the general formula (2) representing the structural unit (B), R ⁶ , R ⁷ and R ⁸ represent a hydrogen atom, an alkyl group or an aryl group, all of which are the same. Or some or all of them may be different. Examples of the alkyl group include a C1 to C8 alkyl group such as a methyl group, an ethyl group, a propyl group, a butyl group, a hexyl group, a 2-ethylhexyl group, and an octyl group. Examples of the aryl group include a phenyl group, a tolyl group, and a vinylphenyl group. In the general formula (2), R ⁶ is preferably a methyl group or a phenyl group. In the general formula (2),
R ⁷ and R ⁸ are each a methyl group, butyl group or a 2-ethylhexyl group, R ⁷ and R ⁸
It is preferable that one of them is an alkyl group and the other is a phenyl group.

In the general formula (2), X ² represents a phenylene group or a methylene phenylene group, wherein the phenylene group and the methylene phenylene group are an o-form, an m-form,
Any of p-forms may be used, but p-forms and m-forms are preferred. The number of repetitions p is 0 or 1.

Specific examples of the structural unit (B) represented by the general formula (2) include a structural unit (N) represented by the following formula (d).
-A structural unit derived from vinyl carbazole), a structural unit represented by the following formula (e) (a structural unit derived from N- (4-vinylphenyl) carbazole), and the following formula (f)
(A structural unit derived from N- (p-vinylbenzyl) carbazole) and a structural unit represented by the following formula (g) (a structural unit derived from N-vinyl-3,6-diphenylcarbazole) And a structural unit represented by the following formula (h) (a structural unit derived from N- (4-vinylphenyl) -3,6-diphenylcarbazole);
A structural unit represented by the formula (N- (p-vinylbenzyl)-
And a structural unit represented by the formula (d) and a structural unit represented by the formula (e).

[0023]

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[0024]

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In the specific copolymer constituting the hole transport layer 10, the ratio of the structural unit (A) to the structural unit (B) is from 5:95 to 95: 5 in molar ratio, and is preferably 2
0: 80-80: 20, more preferably 30: 70-
80:20. When the proportion of the structural unit (B) is too small, the heat resistance of the specific copolymer becomes insufficient, and the obtained hole transport layer 10 material has low hole transport performance. Become. On the other hand, when the proportion of the structural unit (A) is too small, the obtained hole transport layer 10 has low hole transport performance.

The weight average molecular weight of the specific copolymer is, for example, from 3,000 to 1,000,000, particularly preferably 5,000, in terms of polystyrene by gel permeation chromatography.
Preferably it is ~ 300,000. When the weight average molecular weight is less than 3000, the obtained specific copolymer may have insufficient heat resistance, stability in a thin film state, and mechanical strength. On the other hand, when the weight average molecular weight exceeds 1,000,000, the obtained specific copolymer tends to have a remarkably high solution viscosity, and when the hole transport layer 10 is formed by a wet method, the handling property is poor. It is not preferable because the solution is lowered and the solution becomes stringy. Further, the ratio Mw / Mn between the weight average molecular weight and the number average molecular weight is not particularly limited, but is usually 1 to 8, and preferably a value closer to 1.

Such a specific copolymer includes an arylamine-based compound represented by the following general formula (3) (hereinafter referred to as “specific arylamine-based compound”) and a compound represented by the following general formula (4). The represented carbazole derivative (hereinafter referred to as “specific carbazole derivative”) may be used in a suitable polymerization method, for example, a radical polymerization method, an anion polymerization method or a cationic polymerization method, preferably their corresponding living radical polymerization method, It is obtained by copolymerization by an anionic polymerization method or a living cationic polymerization method.

[0028]

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[0029]

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When a specific copolymer is obtained by an ordinary radical polymerization method, azobisisobutyronitrile (A
Azo compounds such as IBN), benzoyl peroxide (BP
A radical polymerization method using a known radical initiator such as a peroxide such as O) or a dithiocarbamate derivative such as tetraethylthiuram disulfide as a polymerization catalyst can be used. Further, when a specific copolymer is obtained by a living radical polymerization method, 2,2,6,6-
Tetramethyl-1-piperidine-N-oxide (TE
A living radical polymerization method using a catalyst system in which an N-oxy radical such as MPO) and the above-mentioned radical polymerization initiator are combined, and a living radical polymerization method such as atom transfer polymerization can be used. The usage ratio of such a radical polymerization catalyst is 1 to 0.00001 mol per 1 mol of the monomer. In such a radical polymerization method, as a polymerization solvent, amide solvents such as dimethylformamide, dimethylacetamide, N-methylpyrrolidone, hydrocarbon solvents such as benzene, toluene, xylene, hexane and cyclohexane, γ-butyrolactone, lactic acid Ester solvents such as ethyl, ketone solvents such as cyclohexylbenzophenone, cyclohexanone, 2-ethylpentanone, and ethyl isoamyl ketone; ether solvents such as cyclic ethers such as tetrahydrofuran and aliphatic ethers such as diethylene glycol dimethyl ether can be used. it can. The reaction temperature is, for example, 0 to 200 ° C., and the reaction time is, for example, 0.5 to 72 hours.

When a specific copolymer is obtained by a usual anionic polymerization method, for example, an olefin catalyst such as naphthyl sodium, methyl lithium, ethyl lithium,
Alkyl lithium such as butyl lithium, aryl lithium such as phenyl lithium, alkyl zinc such as diethyl zinc, lithium alkyl magnesium, alkali metal such as art complex such as lithium alkyl barium,
An anion polymerization method using an organometallic compound of a metal such as an alkaline earth metal as an anion polymerization catalyst can be used. In particular, as the anionic polymerization catalyst, n-
It is preferable to use an organic lithium compound such as butyllithium, sec-butyllithium, and phenyllithium. When a specific copolymer is obtained by a living anion polymerization method, a living anion polymerization method using a catalyst such as butyllithium can be used. The use ratio of such an anionic polymerization catalyst is 0.1 to 0.00001 mol per 1 mol of the monomer. In such an anionic polymerization method, as a polymerization solvent, hydrocarbons such as benzene, toluene, hexane, heptane, and cyclohexane, and ether compounds such as tetrahydrofuran and dioxane can be used. The reaction temperature is, for example, -50 to 100C, and the reaction time is, for example, 5 minutes to 24 hours.

When a specific copolymer is obtained by a usual cation polymerization method, a known cation polymerization catalyst such as trifluoroborate, tin tetrachloride or other Lewis acid, sulfuric acid, hydrochloric acid or other inorganic acid, or a cation exchange resin. Can be used. When a specific copolymer is obtained by a living cationic polymerization method, a living cationic polymerization method using a catalyst such as HI or HI-ZnI ₂ can be used. The use ratio of such a cationic polymerization catalyst is 0.1 to 1 mol of the monomer.
01 to 0.00001 mol. In such a cationic polymerization method, polymerization solvents include halogenated hydrocarbons represented by methylene chloride and chlorobenzene, cyclic ethers such as dibutyl ether, diphenyl ether, dioxane and tetrahydrofuran, and highly polar solvents such as acetonitrile and nitrobenzene. Etc. can be used. The reaction temperature is, for example, -150
To 50 ° C., and the reaction time is, for example, 0.01 to 1
2 hours.

In the hole transport layer 10, various dyes,
A laser dye or the like may be contained, and the ratio is preferably 0.1 to 10% by mass of all materials constituting the hole transport layer 10. By containing such dyes, laser dyes, and the like in the hole transport layer 10,
The obtained organic EL element has a longer use life while emitting light is promoted.

As a light emitting material constituting the light emitting layer 15,
A metal complex of hydroxyquinoline represented by trisquinolinolate aluminum, a metal complex of hydroxybenzoxazole, and a metal complex of hydroxybenzothiazole can be used. The cathode layer 3 is made of a material having a small work function (for example, 4 eV or less), for example, a metal film made of aluminum, calcium, magnesium, lithium, indium, or the like, an alloy film of these metals, or a mixture of these metals and other materials. And an alloy film with such a metal can be used. The thickness of each of the hole transport layer 10 and the light emitting layer 15 is not particularly limited.
It is selected in the range of 10 to 1000 nm, preferably 50 to 200 nm.

Such an organic EL device can be manufactured, for example, as follows. First, an anode layer 2 is formed on the surface of a transparent substrate 1, and a specific copolymer and other materials used as needed are dissolved in an appropriate organic solvent on the surface of the anode layer 2. By applying the hole transport layer forming solution and subjecting the obtained coating film to heat treatment, the organic solvent in the coating film is removed and the hole transport layer 1 is removed.
0 is formed. Next, the light emitting layer 15 is formed on the surface of the hole transport layer 10, and then the cathode layer 3 is formed on the surface of the light emitting layer 15.
Is formed, whereby the organic EL device having the configuration shown in FIG. 1 is manufactured.

In the above, as a method for forming the anode layer 2, a vacuum evaporation method, a sputtering method, or the like can be used. Alternatively, a commercially available material in which, for example, an ITO film is formed on the surface of a transparent substrate such as a glass substrate can be used.

As the organic solvent for preparing the solution for forming the hole transport layer, a material for forming the hole transport layer 10 (a specific copolymer and other materials used as necessary) is dissolved. Obtained are used, and specific examples thereof include chloroform, chlorobenzene, halogenated hydrocarbons such as tetrachloroethane, dimethylformamide,
Amide solvents such as N-methylpyrrolidone, ethyl lactate,
Pegmia, ethyl ethoxypropionate, methyl amyl ketone and the like. These organic solvents can be used alone or in combination of two or more.
Among them, those having an appropriate evaporation rate in terms of obtaining a thin film having a uniform thickness, specifically having a boiling point of 7
It is preferable to use an organic solvent of about 0 to 150 ° C.
The proportion of the organic solvent used depends on the type of the material for forming the hole transport layer 10, but usually the concentration of the material for forming the hole transport layer 10 in the solution for forming the hole transport layer is 0.1%. The ratio is 1 to 10% by weight. As a means for applying the hole transport layer forming solution, for example, a spin coating method, a dipping method, a roll coating method, or the like can be used.

The method for forming the light emitting layer 15 includes (1) a dry method of forming the light emitting layer 15 by vacuum-depositing a light emitting material on the surface of the hole transport layer 10;
(2) A light emitting layer forming solution in which a light emitting material is dissolved in an appropriate organic solvent is applied to the surface of the hole transport layer 15 and subjected to a heat treatment, thereby utilizing a wet method or the like for forming the light emitting layer 15. can do. In the case of using the wet method, as the organic solvent for preparing the light emitting layer forming solution, various ones can be used as long as they can dissolve the light emitting material, and specific examples thereof include toluene, Aromatic hydrocarbons such as xylene, ketones such as methyl isobutyl ketone and cyclohexanone, ethyl lactate, γ-
Esters such as butyrolactone; amides such as N-methylpyrrolidone; alcohols such as 2-ethylhexanol; and halogen compounds such as tetrachloroethane. The usage ratio of the organic solvent varies depending on the type of the light emitting material, but is usually a ratio at which the concentration of the light emitting material in the light emitting layer forming solution is 0.5 to 10% by weight. As a means for applying the light emitting layer forming solution, for example, a spin coating method, a dipping method, a roll coating method, or the like can be used. As a method for forming the cathode layer 3, a vacuum evaporation method, a sputtering method, or the like can be used.

In the organic EL device according to the first embodiment, the anode layer 2 and the cathode layer 3 are
When a DC voltage is applied between the positive electrode and the negative electrode, the hole transport layer 10 and the light emitting layer 15 emit light, and this light is emitted via the anode layer 2 and the glass substrate 1. Organic EL having such a configuration
In the device, since the hole transport layer 10 contains the specific copolymer composed of the structural unit (A) and the structural unit (B), the light emission starting voltage is low, the light emission efficiency is high, and the durability is high. It is excellent.

FIG. 2 is an explanatory sectional view showing the structure of an organic EL device according to a second embodiment of the present invention. The organic EL device according to the first embodiment is different from the organic EL device according to the first embodiment except that the electron transport layer 20 is provided on the light emitting layer 15 and the cathode layer 3 is provided on the electron transport layer 20. It has the same configuration as the element. Examples of the material constituting the electron transport layer 20 include a metal complex of a quinoline-based compound such as an 8-hydroxyquinoline derivative, bisnaphthyloxadiazole,
Oxadiazole-based compounds such as -t-butylphenyl-biphenyl-oxadiazole and 2-naphthyl-5-phenyl-oxadiazole, or polymers containing these residues in the side chain can be used. Such an electron transport layer 20 may be formed by a dry method such as a vacuum evaporation method or a sputtering method, or by dissolving an electron transport material in an appropriate solvent.
The solution can be formed by a wet method in which the solution is applied by a spin coating method, a dipping method, an ink jet method, a printing method, or the like, and dried. In particular, it is preferable to form the electron transport layer 20 by co-evaporating the above-described electron transport material and an alkali metal or an alkaline earth metal. According to the organic EL device according to the second embodiment, the same effects as those of the organic EL device according to the above-described first embodiment can be obtained. In addition, since the electron transport layer 20 is formed, the escape of holes (holes) is prevented, the transport of electrons is smoothed, the emission start voltage is further reduced, and the emission efficiency is further improved. Can be achieved.

FIG. 3 is an explanatory sectional view showing the structure of an organic EL device according to a third embodiment of the present invention. The organic EL device according to the second embodiment is different from the organic EL device according to the second embodiment except that an electron injection layer 25 is provided on the electron transport layer 20 and the cathode layer 3 is provided on the electron injection layer 25. EL
It has the same configuration as the element. As a material constituting the electron injection layer 25, the anode and the electron transport layer are formed from a compound such as a metal fluoride such as LiF, MgF ₂ or CsF, a metal oxide such as AlO ₃ or SrO, or a metal complex such as aluminum. The electron injection layer 25, which can be appropriately selected in consideration of the work function of the constituent material and the LUMO level,
It may be formed on the entire surface of the electron transport layer 20 or may be formed scattered on the surface, and the thickness may be about 0.1 to 20 nm. Such an electron injection layer 25 can be formed by a dry method such as a vacuum evaporation method and a sputtering method. According to the organic EL device according to the third embodiment, the same effects as those of the organic EL devices according to the above-described first and second embodiments can be obtained. Further, since the electron injection layer 25 is formed, the injection of electrons from the anode becomes smooth, the light emission starting voltage is further reduced, and the light emission efficiency can be further improved.

FIG. 4 is an explanatory sectional view showing the structure of an organic EL device according to a fourth embodiment of the present invention. The organic EL device according to the first embodiment is different from the first embodiment except that a hole injection layer 30 is provided on the anode layer 2 and a hole transport layer 10 is provided on the hole injection layer 30. Organic EL related to
It has the same configuration as the element. Examples of the material constituting the hole injection layer 30 include copper phthalocyanine, polyaniline, polythiophene, and a complex of polyethylene dioxythiophene and polystyrene sulfonic acid, which are commercially available under the trade name “PEDOT” (manufactured by Bayer). it can.
Such a hole injection layer 30 may be formed by a dry method such as a vacuum evaporation method or a sputtering method, or by dissolving an electron transport material in an appropriate solvent, and then applying the solution to a spin coating method, a dipping method, an inkjet method, a printing method, or the like. It can be formed by a wet method of coating and drying. In addition, the thickness is 1 to
100 nm. The organic E according to the fourth embodiment
According to the L element, the organic E according to the first embodiment described above is used.
The same effect as that of the L element can be obtained. The hole injection layer 30
Is formed, it is possible to prevent hole injection failure.

FIG. 5 is an explanatory sectional view showing the structure of an organic EL device according to a fifth embodiment of the present invention. The organic EL device according to the fourth embodiment is different from the organic EL device according to the fourth embodiment except that the electron transport layer 20 is provided on the light emitting layer 15 and the cathode layer 3 is provided on the electron transport layer 20. It has the same configuration as the element. As a material constituting the electron transport layer 20, the same material as the organic EL device according to the second embodiment can be used. According to the organic EL device according to the fifth embodiment, the organic EL devices according to the first, second, and fourth embodiments described above.
The same effect as the element can be obtained.

FIG. 6 is an explanatory sectional view showing the structure of an organic EL device according to a sixth embodiment of the present invention. The organic EL device according to the fifth embodiment is different from the organic EL device according to the fifth embodiment except that an electron injection layer 25 is provided on the electron transport layer 20 and the cathode layer 3 is provided on the electron injection layer 25. EL
It has the same configuration as the element. The same material as that of the organic EL device according to the third embodiment can be used as a material forming the electron injection layer 25. According to the organic EL device according to the sixth embodiment, the same effects as those of the organic EL devices according to the above-described first to fourth embodiments can be obtained.

[0045]

Hereinafter, embodiments of the present invention will be described.
The present invention is not limited to these. In the following, “parts” means “parts by mass”.

[Synthesis of Copolymer] <Synthesis Example 1> After the inside of a pressure-resistant bottle having a volume of 50 ml was replaced with nitrogen gas, the pressure-resistant bottle was represented by the following formula (I) under a nitrogen stream. 70 mmol of a compound (hereinafter, referred to as “compound (I)”), 30 mmol of N-vinylcarbazole, and 50 ml of toluene were charged, and the compound (I) and N-vinylcarbazole were dissolved in toluene. While stirring the solution, 10 mmol of azobisisobutyronitrile as a radical polymerization catalyst was added to the solution, and the temperature of the system was raised from room temperature to 70 ° C., and the reaction was carried out at a reaction temperature of 70 ° C. for a reaction time of 20 hours. Polymerization yielded a polymer solution. The polymer was coagulated by pouring the obtained polymer solution into 50 times the amount of methanol to recover the polymer. This polymer was purified by reprecipitation by a conventional method,
Then, it dried under reduced pressure at 50 degreeC for 1 day. Hereinafter, the obtained polymer is referred to as polymer (1). The obtained polymer (1) was subjected to a spectral analysis of an infrared absorption spectrum, and the polymer (1) was found to have a structural unit derived from the compound (I) (a structural unit represented by the formula (a)). And a structural unit derived from N-vinylcarbazole (a structural unit represented by the formula (d)). In this polymer (1), the ratio of the structural unit (A) to the structural unit (B) determined using a calibration curve was 70:30 in molar ratio.

[0047]

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Further, the weight average molecular weight Mw of the polymer (1)
Is 3000 in terms of polystyrene by gel permeation chromatography (solvent: tetrahydrofuran).
0, and the ratio of the weight average molecular weight to the number average molecular weight, Mw /
Mn was 2.6.

<Synthesis Example 2> Instead of 70 mmol of compound (I), 50 mmol of a compound represented by the following formula (II) (hereinafter, referred to as “compound (II)”) was used.
-A polymer was obtained in the same manner as in Synthesis Example 1 except that the amount of vinyl carbazole used was changed to 50 mmol. Hereinafter, the obtained polymer is referred to as polymer (2). The obtained polymer (2) was subjected to spectral analysis of infrared absorption spectrum, which revealed that the polymer (2) was derived from a structural unit derived from the compound (II) (a structural unit represented by the formula (c)) And a structural unit derived from N-vinylcarbazole (a structural unit represented by the formula (d)). In the polymer (2), the ratio of the structural unit (A) to the structural unit (B) is 5 in a molar ratio.
0:50.

[0050]

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Further, the weight average molecular weight Mw of the polymer (2)
Is 3800 in terms of polystyrene by gel permeation chromatography (solvent: tetrahydrofuran).
0, and the ratio of the weight average molecular weight to the number average molecular weight, Mw /
Mn was 1.95.

<Synthesis Example 3> In place of 70 mmol of compound (I), 50 mmol of compound (II) was used.
Instead of 30 mmol of vinylcarbazole, N- (4
A polymer was obtained in the same manner as in Synthesis Example 1 except that 50 mmol of (-vinylphenyl) carbazole was used. Hereinafter, the obtained polymer is referred to as polymer (3). The obtained polymer (3) was subjected to a spectral analysis of an infrared absorption spectrum, and the polymer (3) was found to have a structural unit derived from the compound (II) (a structural unit represented by the formula (c)). And a structural unit derived from N- (4-vinylphenyl) carbazole (a structural unit represented by the formula (e)). In this polymer (3), the ratio of the structural unit (A) to the structural unit (B) was 50:50 in molar ratio.

Further, the weight average molecular weight Mw of the polymer (3)
Is 3300 in terms of polystyrene by gel permeation chromatography (solvent: tetrahydrofuran).
0, and the ratio of the weight average molecular weight to the number average molecular weight, Mw /
Mn was 2.55.

Example 1 A solution for forming a hole transport layer was prepared by dissolving 2 parts of the polymer (1) in 100 parts of m-xylene. A laminated material in which an ITO film (anode layer) is formed on the surface of a transparent substrate made of 5 cm square glass is prepared, and the prepared hole transport layer forming solution is coated on the surface of the ITO film in the laminated material with a spin coater. After the application, the organic solvent was removed by a heat treatment to form a hole transport layer having a thickness of 25 nm.
Next, a light emitting layer made of trisquinolinolate aluminum having a thickness of 50 nm is formed on the hole transporting layer by a vacuum evaporation method, and a surface of the light emitting layer having a thickness of 200 nm and a 5 mm square is formed on the surface of the light emitting layer. By forming an alloy film (cathode layer) of magnesium and silver, an organic EL device having the configuration shown in FIG. 1 was manufactured.

Example 2 An organic EL device was manufactured in the same manner as in Example 1 except that the polymer (2) was used instead of the polymer (1).

Example 3 An organic EL device was manufactured in the same manner as in Example 1 except that the polymer (3) was used instead of the polymer (1).

<Comparative Example 1> Instead of the polymer (1), m
An organic EL device was manufactured in the same manner as in Example 1, except that a polymer of -TPD was used.

Comparative Example 2 An organic EL device was manufactured in the same manner as in Example 1, except that polyvinyl carbazole was used instead of the polymer (1).

[Evaluation of Organic EL Device] (1) Light-Emitting Voltage and Maximum Luminance: Each of the organic EL devices according to Examples 1 to 3 and Comparative Examples 1 and 2 was provided with an ITO film as an anode. The light-emitting layer was made to emit light by applying a DC voltage using the alloy film of magnesium and silver as a cathode, and the maximum light emission luminance was measured with a luminance meter “LS-100” (manufactured by Minolta).
In addition, the light emission starting voltage at that time was measured with a voltmeter “R8240”.
(Manufactured by ADVANTEST). (2) Durability: For each of the organic EL devices according to Examples 1 to 3 and Comparative Examples 1 and 2, the light emitting layer was caused to emit light with the applied current kept constant at 15 mA, and the emission was started from the start of light emission. The time (half-life) until the emission luminance became half of the initial emission luminance was measured, and the organic E according to Comparative Example 2 was measured.
Relative values when the half-life of the L element is 100 (hereinafter, referred to as
It is called "half-life". ). The results are shown in Table 1 below.

[0060]

[Table 1]

As is clear from Table 1, the organic EL devices according to Examples 1 to 3 have higher light emission brightness than the organic EL devices according to Comparative Examples 1 and 2, and 2. The light emission start voltage is lower than that of the organic EL element according to
Moreover, it was confirmed that the organic EL device had better durability than the organic EL devices according to Comparative Examples 1 and 2.

[0062]

As described above, according to the present invention,
It is possible to provide an organic electroluminescence device having a low light emission starting voltage, high light emission efficiency, and excellent durability.

[Brief description of the drawings]

FIG. 1 is an explanatory cross-sectional view showing a configuration of an organic electroluminescence element according to a first embodiment of the present invention.

FIG. 2 is an explanatory cross-sectional view showing a configuration of an organic electroluminescence element according to a second embodiment of the present invention.

FIG. 3 is an explanatory cross-sectional view showing a configuration of an organic electroluminescence element according to a third embodiment of the present invention.

FIG. 4 is an explanatory cross-sectional view showing a configuration of an organic electroluminescence element according to a fourth embodiment of the present invention.

FIG. 5 is an explanatory cross-sectional view showing a configuration of an organic electroluminescence element according to a fifth embodiment of the present invention.

FIG. 6 is an explanatory cross-sectional view showing a configuration of an organic electroluminescence element according to a sixth embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transparent substrate 2 Anode layer 3 Cathode layer 5 DC power supply 10 Hole transport layer 15 Light emitting layer 20 Electron transport layer 25 Electron injection layer 30 Hole injection layer

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Mitsuhiko Sakakibara 2-11-24 Tsukiji, Chuo-ku, Tokyo FSR term in JSR Corporation (reference) 3K007 AB00 AB03 AB06 CA01 CA02 CB01 DA00 DB03 EB00 FA01 4J100 AB07P AB07Q AQ26Q BA04P BA05P BA12P BA15P BA31P BA35P BC43P BC65Q CA04 JA43

Claims (2)

[Claims] 1. A structural unit (A) represented by the following general formula (1) and a structural unit (B) represented by the following general formula (2)
And the structural unit (A) and the structural unit (B)
And a hole transport layer comprising a copolymer having a molar ratio of 5:95 to 95: 5. Embedded image Embedded image 2. The hole transport layer according to claim 1, wherein the molar ratio of the structural unit (A) to the structural unit (B) is 20:80 to 80:20. Claim 1
3. The organic electroluminescent device according to 1.).