JP2002252085A - Organic electric field light-emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic electric field light-emitting element drivable at a low voltage and superior in a heat resistance. SOLUTION: A light-emitting layer 5 pinched by a positive electrode 2 and a negative electrode 7 is formed on a substrate 1, and a positive hole injection layer 3 is formed between the light-emitting layer 5 and the positive electrode 2. The positive hole injection layer 3 contains fluorene containing aromatic amine high polymer having a specific structure and weight average molecular weight of 1,000 to 1,000,000, and contains an electron-accepting compound.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic electroluminescent device, and more particularly, to a thin film device which emits light by applying an electric field to a light emitting layer made of an organic compound.

[0002]

2. Description of the Related Art Conventionally, as a thin film type electroluminescent (EL) element, Zn, which is a group II-VI compound semiconductor of an inorganic material, is used.
In general, S, CaS, SrS, and the like are doped with Mn or a rare earth element (Eu, Ce, Tb, Sm, or the like) which is a luminescence center. However, EL devices manufactured from the above inorganic materials include: 1) AC drive is required (50-1000Hz), 2) High drive voltage (up to 200V), 3) It is difficult to achieve full color, and there is a problem especially with blue color. 4) Cost of peripheral drive circuit is high. are doing.

However, in recent years, in order to improve the above problems,
Development of EL devices using organic thin films has been started. In particular, in order to enhance the luminous efficiency, the type of the electrode was optimized for the purpose of improving the efficiency of carrier injection from the electrode, and a hole transport layer composed of an aromatic diamine and a luminescent layer composed of an aluminum complex of 8-hydroxyquinoline were used. Of an organic electroluminescent device equipped with an organic layer (Appl. Phys. Lett., Vol. 51,
913, 1987), the luminous efficiency has been greatly improved as compared with the conventional EL device using a single crystal such as anthracene or the like, and the practical characteristics have been approached.

In addition to the electroluminescent device using a low molecular material as described above, poly (p-phenylenevinylene) and poly [2-methoxy-5- (2-ethylhexyloxy)- Development of electroluminescent devices using polymer materials such as 1,4-phenylenevinylene], poly (3-alkylthiophene), and polyfluorene, and the use of low-molecular light-emitting materials and electron transfer materials in polymers such as polyvinylcarbazole Development of mixed-dispersed devices is also underway.

By the way, the biggest problem of the organic electroluminescent device is the life during driving. As for the instability during driving,
Examples include a decrease in light emission luminance, an increase in voltage at the time of constant current driving, and generation of a non-light-emitting portion (dark spot). Although there are several causes of these instabilities, deterioration of the thin film shape of the organic layer is dominant. The deterioration of the thin film shape is caused by crystallization (or aggregation) of the organic amorphous film due to heat generated during driving of the device.
It is thought to be caused by such factors. In particular, the contact between the anode and the hole transport layer is important for increasing the drive voltage.

Therefore, in order to improve the contact between the anode and the hole transport layer, it has been studied to provide a hole injection layer between both layers to lower the driving voltage. The conditions required for the material used for the hole injection layer are that a uniform thin film can be formed with good contact with the anode and that it is thermally stable, that is, the melting point and the glass transition temperature (Tg) are high. It is required to have a melting point of 300 ° C or higher and a glass transition temperature of 100 ° C or higher. In addition, the ionization potential is low, holes can be easily injected from the anode, and the hole mobility is high.

Conventionally, various materials have been studied as a material for the hole injection layer. For example, porphyrin derivatives and phthalocyanine compounds (Japanese Patent Application Laid-Open No. 63-295695), starburst type aromatic triamines (Japanese Patent Application Laid-Open No. No. 308688), organic compounds such as polythienylenevinylene, polythiophene and polyaniline, sputtered carbon films,
Metal oxides such as vanadium oxide, ruthenium oxide, and molybdenum oxide have been reported.

[0008]

However, when a porphyrin derivative or a phthalocyanine compound is used as the hole injection layer in the method of inserting the hole injection layer between the anode and the hole transport layer, these films themselves are not used. There is a problem that the spectrum is changed due to light absorption by the light source, or the external appearance is colored and becomes invisible.

[0009] Starburst-type aromatic triamines have the advantage of low ionization potential and good transparency, but have difficulty in heat resistance due to their low glass transition point and melting point.

[0010] Conjugated polymers such as polythienylenevinylene, polythiophene and polyaniline have a problem in solubility and a problem in the production process.

Attempts have also been made to use a non-conjugated polymer in which no electron-accepting compound is mixed as a hole transport layer (JP-A-9-188756 and JP-A-11-135262). The efficiency of the element is described in JP-A-9-188756, 17
As shown in FIG. 4, the driving voltage is as high as ²⁰ cd / m ^{2 at} 6 V, and the luminous efficiency at that time is as low as 1 cd / A.

Furthermore, it is disclosed that low voltage driving is possible by mixing an electron-accepting compound with a non-conjugated hole transporting polymer (Japanese Patent Application Laid-Open No. 11-283750). There is no description that the resulting polymer has a low glass transition temperature Tg and improved heat resistance.

As described above, the fact that the voltage at the time of driving the organic electroluminescent element is high and the stability including heat resistance is low is as follows.
This is a serious problem as a light source for a facsimile, a copying machine, a backlight of a liquid crystal display, etc., and is particularly undesirable as a display element for a full-color flat panel display.

Further, indium tin oxide (ITO) usually used as an anode in a conventional organic electroluminescent device
In addition to having a surface roughness of about 10 nm (Ra), the semiconductor device often has local protrusions, and has a problem that short-circuit defects occur during device fabrication.

The present invention solves the above-mentioned conventional problems, can be driven at low voltage and high luminous efficiency, has good heat resistance, and maintains stable luminous characteristics for a long period of time. It is an object of the present invention to provide an organic electroluminescent device capable of performing the above.

Another object of the present invention is to provide an organic electroluminescent device which can prevent short-circuit defects at the time of device fabrication due to the above-mentioned surface roughness of the anode.

[0017]

According to the present invention, there is provided an organic electroluminescent device having an anode, a cathode and a light emitting layer present between the two electrodes on a substrate. A layer containing a fluorene-containing aromatic amine polymer having a repeating unit represented by the following general formula (I), and having a weight average molecular weight of 1,000 to 1,000,000, and an electron-accepting compound. An organic electroluminescent device characterized in that:

[0018]

Embedded image (Wherein, ring D and ring E each independently represent a benzene ring which may have a substituent, and R ¹ and R ² each independently represent a hydrogen atom, a halogen atom, an alkyl group, an aralkyl group, Alkenyl group, cyano group, amino group, acyl group, alkoxycarbonyl group, carboxyl group, alkoxy group, aryloxy group, alkylamino group, haloalkyl group, hydroxyl group, aromatic hydrocarbon ring group which may have a substituent Or Ar represents an aromatic heterocyclic group, and Ar represents an aromatic hydrocarbon ring group or an aromatic heterocyclic group which may have a substituent.)

By having the repeating unit represented by the general formula (I), the fluorene-containing aromatic amine polymer tends to show a relatively high glass transition temperature Tg.

That is, the present inventors have intensively studied to solve the conventional problems and to provide an organic electroluminescent device capable of maintaining stable light emitting characteristics at a high temperature.
In an organic electroluminescent device having a light emitting layer sandwiched by an anode and a cathode, a specific fluorene-containing aromatic amine containing an electron accepting compound between the anode and the light emitting layer, and having a high glass transition temperature Tg It has been found that the above-mentioned problems can be solved by providing a layer having a polymer as a base, and the present invention has been completed.

In the present invention, by mixing and using a specific fluorene-containing aromatic amine polymer having a high Tg and an electron-accepting compound, it is possible to simultaneously improve the luminous characteristics and heat resistance of the device. did. That is, by mixing the electron-accepting compound with the electron-donating fluorene-containing aromatic amine polymer, charge transfer occurs, and as a result, holes serving as free carriers are generated, and the electric conductivity of this layer increases. . By providing such a layer, the electrical connection between the light emitting layer and the anode is improved, and the driving voltage is reduced, and at the same time, the stability during continuous driving is also improved. Also, for example, 10
By using a specific fluorene-containing aromatic amine polymer having a high glass transition temperature of 0 ° C. or higher as a base, the heat resistance of the device is also greatly improved. The glass transition temperature of the fluorene-containing aromatic amine polymer used in the present invention is particularly 120.
C. or higher, particularly preferably 150.degree. C. or higher.

Further, by forming such a layer having a polymer material as a base on the anode by a coating process, the surface roughness of the anode is reduced, and a good surface smoothing effect is obtained. There is also an effect that a short circuit defect at the time of fabrication is prevented.

The layer containing the fluorene-containing aromatic amine polymer and the electron-accepting compound according to the present invention is a layer exhibiting a hole transporting property and may be located anywhere between the anode and the light emitting layer. As shown in FIGS. 1 to 3, which will be described later, the layer is not limited to the one provided in contact with the anode. However, the advantage of this layer that the electric connection with the anode (inorganic material) is good and the heat resistance is high is high. In order to make full use of it, it is most advantageous to form a hole injection layer at a position in contact with the anode.

In the present invention, the value obtained by subtracting the electron affinity of the electron-accepting compound from the ionization potential of the fluorene-containing aromatic amine polymer is preferably 0.7 eV or less. The content of the acceptor compound is preferably in the range of 0.1 to 50% by weight based on the fluorene-containing aromatic amine polymer.

In the present invention, the electron accepting compound is preferably a compound represented by the following general formula (II) or at least one compound selected from the following compound group.

[0026]

Embedded image (In the formula, X represents a halogen atom, and rings A, B, and C each independently represent a benzene ring which may have a substituent.)

[0027]

Embedded image

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the organic electroluminescent device of the present invention will be described in detail with reference to the drawings.

1 to 3 are schematic cross-sectional views showing an embodiment of the organic electroluminescent device of the present invention, wherein 1 is a substrate, 2 is an anode, 3 is a hole injection layer, and 4 is a hole transport layer. 5 is a light emitting layer,
6 represents an electron transport layer, and 7 represents a cathode.

The substrate 1 serves as a support for the organic electroluminescent element, and is made of a quartz or glass plate, a metal plate or a metal foil, a plastic film or a sheet, or the like. Particularly, a glass plate or a plate of a transparent synthetic resin such as polyester, polymethacrylate, polycarbonate, and polysulfone is preferable. When using a synthetic resin substrate, it is necessary to pay attention to gas barrier properties. If the gas barrier property of the substrate is too low, the organic air-emitting device may be deteriorated by outside air passing through the substrate, which is not preferable. Therefore, a method of providing a dense silicon oxide film or the like on one or both sides of the synthetic resin substrate to ensure gas barrier properties is also a preferable method.

The anode 2 is provided on the substrate 1, and the anode 2 plays a role of injecting holes into the hole injection layer 3. The anode is usually made of a metal such as aluminum, gold, silver, nickel, palladium, and platinum; a metal oxide such as an oxide of indium and / or tin; a metal halide such as copper iodide; and carbon black. You. Usually, the formation of the anode 2 is often performed by a sputtering method, a vacuum evaporation method, or the like. Further, the anode 2 is formed by dispersing metal fine particles such as silver, fine particles such as copper iodide, carbon black, conductive metal oxide fine particles, and the like in an appropriate binder resin solution and applying the dispersion on the substrate 1. Can also. The anode 2 can be formed by laminating different materials. The thickness of the anode 2 depends on the required transparency. When transparency is required, the transmittance of visible light is usually 60% or more, preferably 80% or more. In this case, the thickness is usually 10 to 1000 n.
m, preferably about 20 to 500 nm. If opaque, the anode 2 may be the same as the substrate 1. Further, a layer made of a different conductive material can be laminated on the interface of the anode 2 on the light emitting layer side.

In the device structure shown in FIGS. 1 to 3, a hole injection layer 3 is provided on an anode 2. Generally, the conditions required for the material used for the hole injection layer 3 include:
It is a material having a high hole injection efficiency from the anode 2 and capable of efficiently transporting the injected holes. For that purpose, the ionization potential is small, the transparency to visible light is high, the hole mobility is large, the stability is high, and impurities serving as traps are unlikely to be generated during production or use. Required.
In addition to the above general requirements, in view of application to in-vehicle display, those having a heat resistance of 100 ° C. or more are preferable.

In the organic electroluminescent device of the present invention, preferably, the hole injecting layer 3 has a weight average molecular weight of 1,000 to 1,000,000 having a repeating unit represented by the general formula (I).
The layer preferably contains 1,000 to 100,000 fluorene-containing aromatic amine polymer and an electron-accepting compound.

In the present invention, the high glass transition temperature Tg
By mixing and using a specific fluorene-containing aromatic amine polymer having an electron-accepting compound, the light-emitting characteristics and heat resistance of the device can be simultaneously improved. That is,
By mixing an electron-accepting compound with an electron-donating fluorene-containing aromatic amine polymer, charge transfer occurs, resulting in the generation of holes as free carriers and an increase in the electrical conductivity of the hole injection layer. . For this reason, by providing such a hole injection layer, the electrical junction between the light emitting layer and the anode is improved, and the driving voltage is reduced, and at the same time, the stability during continuous driving is also improved. Further, by using an aromatic amine-containing polymer having a high glass transition temperature Tg of, for example, 100 ° C. or more as a base material of the hole injection layer, the heat resistance of the device is greatly improved. The glass transition temperature of the fluorene-containing aromatic amine polymer used in the present invention is particularly 120 ° C or higher, especially 1 ° C.
Preferably it is 50 ° C. or higher.

In the general formula (I), ring D and ring E
Represents a benzene ring which may have a substituent independently of each other, and examples of the substituent include groups described below as R ¹ and R ² .

R ¹ and R ² each independently represent a hydrogen atom; a halogen atom;
Preferably an alkyl group of 4 to 12; an aralkyl group such as a benzyl group; an alkenyl group such as a vinyl group; a cyano group; an amino group; an acyl group; an alkoxycarbonyl group having 2 to 9 carbon atoms such as a methoxycarbonyl group and an ethoxycarbonyl group. ;
Carboxyl group; carbon number 1 such as methoxy group and ethoxy group
Aryloxy groups such as phenoxy group and benzyloxy group; alkylamino groups such as methylamino group, dimethylamino group, diethylamino group and diisopropylamino group; haloalkyl groups such as trifluoromethyl group; hydroxyl group; An aromatic hydrocarbon ring group such as a phenyl group or a naphthyl group which may have a group; an aromatic heterocyclic group such as a thienyl group or a pyridyl group which may have a substituent; Is a halogen atom such as a fluorine atom; an alkyl group having 1 to 6 carbon atoms such as a methyl group and an ethyl group; an alkenyl group such as a vinyl group; an alkoxycarbonyl group having 1 to 6 carbon atoms such as a methoxycarbonyl group and an ethoxycarbonyl group. An alkoxy group having 1 to 6 carbon atoms such as a methoxy group and an ethoxy group; an aryloxy group such as a phenoxy group and a benzyloxy group; Group; methylamino group, dimethylamino group, an alkylamino group such as a diethylamino group; an acyl group such as an acetyl group, a haloalkyl group such as trifluoromethyl group, a cyano group.

Ar is an aromatic hydrocarbon group or an aromatic heterocyclic group which may have a substituent, preferably a 5- or 6-membered aromatic monocyclic ring, or a condensed two or three of these. Or represents a group directly bonded, preferably, each may have a substituent, phenyl group, naphthyl group, anthryl group, pyridyl group, triazyl group, pyrazyl group,
Examples of the substituent include a halogen atom; an alkyl group having 1 to 6 carbon atoms such as a methyl group and an ethyl group; an alkenyl group such as a vinyl group; a methoxycarbonyl group and an ethoxycarbonyl group. An alkoxycarbonyl group having 1 to 6 carbon atoms such as methoxy group, ethoxy group and the like; an alkoxy group having 1 to 6 carbon atoms such as methoxy group and ethoxy group; an aryloxy group such as phenoxy group and benzyloxy group;
Examples thereof include a dialkylamino group such as a diethylamino group and a diisopropylamino group.

The fluorene-containing aromatic amine polymer having a repeating unit represented by the general formula (I) is synthesized by, for example, a two-step reaction using the following raw materials.

[0039]

Embedded image

In the reaction 1, for example, bromination is carried out by adding bromine in a chloroform solvent using ferric chloride as a catalyst. In the reaction 2, the dibromo compound and the aromatic amine produced in the reaction 1 are converted into an orthoxylene solvent. It is dissolved and reacted under a nitrogen atmosphere using a palladium catalyst for a reaction time of about 24 hours. The obtained product is purified by reprecipitation to obtain a fluorene-containing aromatic amine polymer.

The fluorene-containing aromatic amine polymer according to the present invention is most preferably a homopolymer (homopolymer) composed of only the repeating unit represented by the above general formula (I). May be a copolymer (copolymer) containing a repeating unit other than the general formula (I) as long as the above does not impair. When the fluorene-containing aromatic amine polymer according to the present invention is a copolymer, the content of the repeating unit other than the general formula (I) in the copolymer is preferably 50 mol% or less, particularly preferably 20 mol% or less. , Most preferably 0%, ie the general formula (I)
Is a homopolymer consisting of only the repeating unit represented by The repeating unit represented by the general formula (I) is 1
More than one kind may be contained in the molecule.

Preferred specific examples of the fluorene-containing aromatic amine polymer having a repeating unit represented by the general formula (I) are shown in Tables 1 and 2, but are not limited thereto.

[0043]

[Table 1]

[0044]

[Table 2]

The electron-accepting compound used in combination with the above-mentioned fluorene-containing aromatic amine polymer may be any as long as it causes charge transfer with the fluorene-containing aromatic amine polymer. As a result of consideration,
The two physical property values of the ionization potential IP (polymer) of the fluorene-containing aromatic amine polymer and the electron affinity EA (acceptor) of the electron accepting compound (acceptor) are as follows: IP (polymer) −EA (acceptor) ≦ 0.7 It has been found that when expressed by the relational expression of eV, it is more effective in achieving the object of the present invention.

This will be described with reference to the energy level diagram of FIG. Generally, the ionization potential and the electron affinity are determined based on the vacuum level. The ionization potential is defined as the energy required to release electrons at the HOMO (highest occupied molecular orbital) level of a substance to a vacuum level, and the electron affinity is determined by the LUMO (lowest empty molecule) of the substance at a vacuum level. Orbit) is defined as the energy that falls to a level and stabilizes. In the present invention, the HOMO level ionization potential of the fluorene-containing aromatic amine polymer shown in FIG.
It is preferable that the difference from the level of electron affinity is 0.7 eV or less. The ionization potential is directly measured by photoelectron spectroscopy, but can also be obtained by correcting the electrochemically measured oxidation potential with respect to a reference electrode. In the latter case,
For example, when a saturated sweet potato electrode (SCE) is used as a reference electrode, ionization potential = oxidation potential (vs. SCE) + 4.3 eV ("Molecular Semiconductors", Springer-V
erlag, 1985, p. 98). The electron affinity can be obtained by subtracting the optical band gap from the above-mentioned ionization potential, or similarly from the above-mentioned formula from the electrochemical reduction potential.

The relational expression between the ionization potential and the electron affinity can be expressed by using the oxidation potential and the reduction potential as follows: oxidation potential of polymer−reduction potential of acceptor ≦ 0.7 eV.

IP (polymer) -EA (acceptor)
Is substantially about -0.7 eV.

The content of the electron-accepting compound in the hole injection layer 3 is based on the amount of the fluorene-containing aromatic amine polymer.
Preferably it is in the range of 0.1 to 50% by weight. More preferably, a concentration range of 1 to 30% by weight is desirable in practical characteristics.

The electron accepting compound is not particularly limited as long as it satisfies the above relationship, but is preferably selected from compounds represented by the following general formula (II).

[0051]

Embedded image (Wherein X represents a halogen atom, and rings A, B and C are
Each independently represents a benzene ring which may have a substituent. )

In the general formula (II), preferably,
In the formula, X represents a halogen atom such as chlorine, fluorine and bromine, and preferably represents a hydrogen atom; a halogen atom such as chlorine, fluorine and bromine; a methyl group;
An alkyl group having 1 to 6 carbon atoms such as an ethyl group; a haloalkyl group such as a trifluoromethyl group; a cyano group; and a nitro group. The substitution position of these substituents may be any of the ortho, meta and para positions with respect to the central nitrogen atom.

Specific examples of the electron-accepting compound represented by the general formula (II) include the following compounds.

[0054]

Embedded image

Other preferred examples of the electron accepting compound are shown below with their abbreviations.

[0056]

Embedded image

In the present invention, the hole injection layer 3 containing the fluorene-containing aromatic amine polymer and the electron accepting compound is formed on the anode 2 by a coating method. For example, a predetermined amount of the fluorene-containing aromatic amine polymer and the electron-accepting compound is added, if necessary, to an additive such as a binder resin or a coating improver that does not trap holes, and dissolved to prepare a coating solution. Then, the hole injection layer 3 is formed by applying the solution on the anode 2 by a method such as a spin coating method or a dip coating method, and then drying.

As described above, in the conventional organic electroluminescent device, there was a problem of short-circuiting at the time of manufacturing the device due to the surface roughness of the anode 2 such as ITO. However, such a fluorene-containing aromatic amine polymer was used. The hole injecting layer 3 formed by applying the coating solution containing the solution has a smooth surface, so that the problem of the short circuit can be solved.

The thickness of the hole injection layer 3 thus formed is usually 5 to 1000 nm, preferably 10 to 500 nm.

The light emitting layer 5 is provided on the hole injection layer 3. The light-emitting layer 5 is made of a material that efficiently recombines electrons injected from the cathode and holes transported from the hole injection layer 3 between the electrodes to which an electric field is applied, and emits light efficiently by the recombination. It is formed.

As a material satisfying such conditions, 8
Metal complexes such as aluminum complexes of -hydroxyquinoline (JP-A-59-194393);
[h] quinoline metal complex (JP-A-6-322362),
Bisstyrylbenzene derivatives (Japanese Patent Application Laid-Open Nos. 1-245087 and 2-222484), bisstyrylarylene derivatives (Japanese Patent Application Laid-Open No. 2-247278), and metal complexes of (2-hydroxyphenyl) benzothiazole (Japanese Patent Application Laid-Open No. −315983
Publication), silole derivatives and the like. These light emitting layer materials are usually laminated on the hole injection layer 3 by a vacuum evaporation method.

For the purpose of improving the luminous efficiency of the device and changing the luminescent color, for example, doping a fluorescent dye for laser such as coumarin using an 8-hydroxyquinoline aluminum complex as a host material (J. Appl. Phys. , 65
Vol. 3610, 1989).

For the purpose of improving the driving life of the device, it is effective to dope a fluorescent dye by using the light emitting layer material as a host material. For example, using a metal complex such as an aluminum complex of 8-hydroxyquinoline as a host material, a naphthacene derivative represented by rubrene (Japanese Patent Laid-Open No. 4-335087) and a quinacridone derivative (Japanese Patent Laid-Open No.
No. 70773), condensed polycyclic aromatic rings such as perylene (JP-A-5-198377) are added to the host material in an amount of 0.1 to 0.1%.
By doping at 10% by weight, the light emitting characteristics of the device, particularly the driving stability, can be greatly improved. As a method of doping a fluorescent dye such as the naphthacene derivative, quinacridone derivative, or perylene into the host material of the light-emitting layer,
There are a method of co-evaporation and a method of mixing evaporation sources at a predetermined concentration in advance.

Examples of the polymer-based light emitting layer materials include poly (p-phenylenevinylene) and poly [2-methoxy-5] described above.
-(2-ethylhexyloxy) -1,4-phenylenevinylene], a polymer material such as poly (3-alkylthiophene), a system in which a luminescent material and an electron transfer material are mixed with a polymer such as polyvinylcarbazole, and the like. Can be These materials are applied on the hole injection layer 3 by a method such as spin coating or dip coating in the same manner as in the case of the hole injection layer to be thinned.

The thickness of the light emitting layer 5 thus formed is usually 10 to 200 nm, preferably 30 to 100 nm.

In order to improve the light emission characteristics of the device, FIG.
As shown in FIG. 3, a hole transport layer 4 is provided between the hole injection layer 3 and the light emitting layer 5, and an electron transport layer 6 is provided between the light emitting layer 5 and the cathode 7 as shown in FIG. For example, a so-called function-separated element may be provided.

In the function-separated element shown in FIGS. 2 and 3,
The material of the hole transport layer 4 needs to be a material having high hole injection efficiency from the hole injection layer 3 and capable of efficiently transporting the injected holes. For that purpose, it is required that the ionization potential is small, the hole mobility is large, the stability is further excellent, and impurities serving as traps are hardly generated during production or use. In addition, since the layer is in direct contact with the light-emitting layer 5, it is preferable that a substance that quenches light emission is not included.

As such a hole transport material, for example, 4,4′-bis [N- (1-naphthyl) -N-phenylamino]
Containing two or more tertiary amines represented by biphenyl;
Aromatic diamines in which at least two condensed aromatic rings are substituted with nitrogen atoms (JP-A-5-234681), 4,4 ', 4 "-tris (1-
Aromatic amine compounds having a starburst structure such as naphthylphenylamino) triphenylamine (J. Lumi
n., 72-74, 985, 1997), an aromatic amine compound comprising a tetramer of triphenylamine (Chem. Commun., 21).
75, 1996), spiro compounds such as 2,2 ', 7,7'-tetrakis- (diphenylamino) -9,9'-spirobifluorene (Syn
th. Metals, vol. 91, p. 209, 1997).
These compounds may be used alone or, if necessary, in combination of two or more.

In addition to the above compounds, as a material of the hole transport layer 4, polyarylene ether sulfone containing polyvinyl carbazole, polyvinyl triphenylamine (Japanese Patent Laid-Open No. 7-39553), and tetraphenylbenzidine (Polym. Tech., 7, 33, 1996).

The hole transport layer 4 is formed by laminating the above hole transport material on the hole injection layer 3 by a coating method or a vacuum evaporation method.

In the case of the coating method, one or more hole transport materials and, if necessary, additives such as a binder resin or a coating property improving agent which do not trap holes are added and dissolved to form a coating solution. Is prepared, applied on the hole injection layer 3 by a method such as spin coating, and dried to form the hole transport layer 4. Here, examples of the binder resin include polycarbonate, polyarylate, and polyester. If the amount of the binder resin added is large, the hole mobility is lowered. Therefore, a small amount is desirable, and usually 50% by weight or less is preferable.

In the case of the vacuum evaporation method, the hole transporting material is put into a crucible provided in a vacuum vessel, and the inside of the vacuum vessel is evacuated to about 10 ⁻⁴ Pa by a suitable vacuum pump, and then the crucible is heated. Then, the hole transporting material is evaporated, and the hole transporting layer 4 is formed on the substrate 1 on which the anode 2 and the hole injection layer 3 are formed facing the crucible.

The thickness of the hole transport layer 4 thus formed is usually 10 to 300 nm, preferably 30 to 100 nm.
In order to uniformly form such a thin film, generally, a vacuum deposition method is often used.

The compound used for the electron transporting layer 6 in FIG. 3 is required to be capable of easily injecting electrons from the cathode and having a higher electron transporting ability. As such an electron transporting material, the 8-emitting material already mentioned as the light emitting layer material is used.
Aluminum complex of hydroxyquinoline, oxadiazole derivative (Appl. Phys. Lett., 55, 1489, 1989)
Years) and those polymethyl methacrylate (PMMA)
A phenanthroline derivative (JP-A-5-331459), 2-t-butyl-9,10-N, N'-dicyanoanthraquinone diimine, n-type hydrogenated amorphous silicon carbide, Examples include n-type zinc sulfide and n-type zinc selenide.

The thickness of the electron transport layer 6 is usually 5 to 200 nm, preferably 10 to 100 nm.

The cathode 7 plays a role of injecting electrons into the light emitting layer 5 in FIGS. 1 and 2 or the electron transport layer 6 in FIG. As the material used for the cathode 7, the material used for the anode 2 can be used, but for efficient electron injection, a metal having a low work function is preferable, and tin, magnesium, indium, calcium, A suitable metal such as aluminum or silver or an alloy thereof is used. Specific examples include a low work function alloy electrode such as a magnesium-silver alloy, a magnesium-indium alloy, and an aluminum-lithium alloy.

The thickness of the cathode 7 is usually the same as that of the anode 2. Laminating a metal layer having a high work function and being stable to the atmosphere on the cathode 7 for the purpose of protecting the cathode made of a low work function metal is effective for increasing the stability of the device. For this purpose, metals such as aluminum, silver, copper, nickel, chromium, gold, platinum and the like are used.

Further, an ultra-thin insulating film (film thickness: 0.1 to 5 nm) such as LiF, MgF ₂ , or Li ₂ O may be inserted at the interface between the cathode 7 and the light emitting layer 5 or the electron transporting layer 6. This is an effective method for improving the quality of life (Appl. Phys. Lett., 70, 152
Page, 1997; JP-A-10-74586; IEEE Trans. El.
ectron. Devices, 44, 1245, 1997).

FIGS. 1 to 3 show an example of an element structure employed in the present invention, and the present invention is not limited to the illustrated one. For example, it is also possible to stack the cathode 7, the light emitting layer 5, the hole injection layer 3, and the anode 2 in this order on the substrate 1, that is, at least one of them is transparent as described above. It is also possible to provide the organic electroluminescent device of the present invention between two highly-substrate substrates. Similarly, the components shown in FIGS. 2 and 3 can be stacked in the opposite structure. Further, an arbitrary layer other than the above-described layers may be formed between the respective layers.

[0080]

Now, the present invention will be described more specifically with reference to Synthesis Examples, Experimental Examples, Comparative Experimental Examples, Examples and Comparative Examples.
The present invention is not limited to the description of the following examples unless it exceeds the gist.

Synthesis Example 1 A fluorene-containing aromatic amine polymer (homopolymer) consisting of only the repeating units shown in (3) of Table 1 (hereinafter referred to as “polymer (3)”) was reacted under the following reaction conditions. Was synthesized.

9,9-Dioctylfluorene (17.9 mmol) was dissolved in chloroform, cooled to 0 ° C., and ferric chloride (0.42 mmol) and bromine (41.2 mmol) were added thereto.
Allowed to react for hours. After completion of the reaction, the mixture was poured into water and neutralized with sodium thiosulfate until the red solution turned white.
Then, the organic layer was extracted three times with chloroform. It was dried over magnesium sulfate overnight. Thereafter, the mixture was filtered and chloroform was removed with an evaporator to obtain a light brown solid. This solid is dissolved in hexane, subjected to column chromatography (developing solvent n-hexane), recrystallized with methanol, and dried in vacuum (40 ° C. for 12 hours).
As a result, 2,7-dibromo-9,9-dioctylfluorene was obtained as a white solid. Identification was performed by ¹ H-NMR and IR.
The yield was 49% (30 g).

The 2,7-dibromo-9,9-dioctylfluorene (3.65 mmol), aniline (3.6 mmol),
Diphenylamine (0.055mmo
l), t-butylphosphine (1.46 mmol), palladium acetate (0.182 mmol), sodium tert-butylate (7.2
9 mmol) and o-xylene (24.4 ml) under nitrogen atmosphere.
Reflux at 24 ° C. for 24 hours. After the completion of the reaction, ion-exchanged water was added. After filtration using THF as an extraction solvent, purification was carried out by reprecipitation purification (methanol poor solvent: chloroform good solvent or THF). When the structure of the final product was confirmed by ¹ H-NMR and IR, it was confirmed that the desired fluorene-containing aromatic amine polymer was synthesized. The yield was 63%, and the molecular weight of the obtained polymer (3) was number average molecular weight 15,800, weight average molecular weight 35,000, and molecular weight distribution 2.2. Glass transition temperature was 268 ° C.

Synthesis Example 2 A fluorene-containing aromatic amine polymer (homopolymer) (hereinafter referred to as “polymer (5)”) consisting of only the repeating unit shown in (5) of Table 1 was used in the same manner as in Synthesis Example 1. Under the following reaction conditions. When the structure of the final product was confirmed by ¹ H-NMR and IR, it was confirmed that the desired fluorene-containing aromatic amine polymer was synthesized. The yield is
The molecular weight of the obtained polymer (5) was 58,000, the number average molecular weight was 7,000, the weight average molecular weight was 16,700, and the molecular weight distribution was 2.4. Glass transition temperature was 266 ° C.

Synthesis Example 3 A fluorene-containing aromatic amine polymer (homopolymer) consisting of only the repeating units shown in (6) of Table 1 (hereinafter referred to as “polymer (6)”) was prepared in the same manner as in Synthesis Example 1. Under the following reaction conditions. When the structure of the final product was confirmed by ¹ H-NMR and IR, it was confirmed that the desired fluorene-containing aromatic amine polymer was synthesized. The yield is
With a molecular weight of 43%, the obtained polymer (6) had a number average molecular weight of 6,400, a weight average molecular weight of 11,600 and a molecular weight distribution of 1.8. Glass transition temperature was 260 ° C.

Experimental Example 1 A glass substrate was subjected to ultrasonic cleaning with acetone, water cleaning with pure water, ultrasonic cleaning with isopropyl alcohol, and drying with dry nitrogen.
After performing UV / ozone cleaning, the polymer (3) obtained in Synthesis Example 1 was spin-coated on the glass substrate under the following conditions. Solvent 1,2-dichloroethane Coating solution concentration 5 [mg / ml] Spinner rotation speed 2000 [rpm] Spinner rotation time 30 [sec] Drying condition Nitrogen atmosphere 120 ° C-1 hour drying

A uniform thin film having a thickness of 40 nm was formed by the above spin coating. The ionization potential of this thin film sample was measured using an ultraviolet electron analyzer (AC, manufactured by Riken Keiki Co., Ltd.).
When measured using -1), a value of 5.30 eV was shown.

An electron accepting compound represented by the following structural formula:
For TBPAH (tris (4-bromophenyl) aminium hexachloroantimonate), the reduction potential is
1.06V [vs.SCE], the electron affinity is
5.36 eV. Therefore, the difference from the ionization potential of the polymer (3) is -0.06 eV.

[0089]

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Experimental Example 2 The polymer (3) obtained in Synthetic Example 1 was mixed with TBPAH as an electron accepting compound, and spin-coated on a glass substrate in the same manner as in Experimental Example 1.

By this spin coating, a uniform thin film having a thickness of 30 nm and containing 80% by weight of the polymer (3) and 20% by weight of TBPAH was formed. As a result of measuring the absorption spectrum of the visible portion of the thin film sample, a transparent film having a transmittance of 90% or more in a wavelength range of 400 to 700 nm was obtained.

Comparative Experimental Example 1 A glass substrate washed in the same manner as in Experimental Example 1 was set in a vacuum evaporation apparatus. After the rough evacuation of the above apparatus was performed by an oil rotary pump, the degree of vacuum in the apparatus was 2 × 10 ⁻⁶ Torr (about 2.7 ×
Evacuation was performed using an oil diffusion pump equipped with a liquid nitrogen trap until the pressure became 10 ^-4 Pa) or less. The copper phthalocyanine represented by the following structural formula, which was placed in a molybdenum boat placed in the above apparatus, was heated to perform vapor deposition. The degree of vacuum during deposition is 2 × 10 ^-6 Torr (about 2.7 × 10 ^-4 Pa), deposition rate 0.2
A film having a thickness of 20 nm was formed at a rate of nm / sec.

[0093]

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As a result of measuring the transmission spectrum of the visible portion of this thin film sample, absorption was observed in the wavelength region of 550 to 700 nm, and the transmittance was 80%. This film may have problems in application to full color display. confirmed.

EXPERIMENTAL EXAMPLE 3 Spin coating was performed on a glass substrate in the same manner as in Experimental Example 1 except that the polymer (5) obtained in Synthesis Example 2 was used as the aromatic amine-containing polymer, and a polymer having a thickness of 40 nm was obtained. A thin film having a uniform thickness was formed. When the ionization potential of this thin film sample was measured, it showed a value of 5.10 eV.

Accordingly, it was confirmed that the difference between the ionization potential of the polymer (5) and the electron affinity of TBPAH, which is an electron accepting compound, was -0.26 eV.

Experimental Example 4 Spin coating was performed on a glass substrate in the same manner as in Experimental Example 1 except that the polymer (6) obtained in Synthesis Example 3 was used as the aromatic amine-containing polymer. A thin film having a uniform thickness was formed. When the ionization potential of this thin film sample was measured, it showed a value of 5.20 eV.

Therefore, it was confirmed that the difference between the ionization potential of this polymer (6) and the electron affinity of TBPAH, which is an electron accepting compound, was -0.16 eV.

Example 1 An organic electroluminescent device having the structure shown in FIG. 2 was manufactured by the following method.

An indium tin oxide (ITO) transparent conductive film deposited on a glass substrate in a thickness of 120 nm (sheet resistance: 15 Ω) was patterned into 2 mm-wide stripes using ordinary photolithography and hydrochloric acid etching to form an anode 2. Was formed. The patterned ITO substrate was cleaned in the order of ultrasonic cleaning with acetone, water cleaning with pure water, and ultrasonic cleaning with isopropyl alcohol, dried with nitrogen blow, and finally cleaned with ultraviolet and ozone.

A mixture of the polymer (3) obtained in Synthesis Example 1 and TBPAH was placed on this ITO glass substrate in Experimental Example 2.
The hole injection layer 3 having a uniform thin film shape with a thickness of 30 nm was formed by spin coating under the same conditions as described above.

Next, the substrate 1 on which the hole injection layer 3 was coated and formed was set in a vacuum evaporation apparatus. After rough exhaust of the above device was performed by an oil rotary pump, the degree of vacuum in the device was 2 × 10
Evacuation was performed using an oil diffusion pump equipped with a liquid nitrogen trap until the pressure became ^-6 Torr (about 2.7 × 10 ^-4 Pa) or less. An aromatic amine compound represented by the following structural formula and placed in a ceramic crucible placed in the above apparatus: 4,4′-bis [N- (1-
[Naphthyl) -N-phenylamino] biphenyl was heated for vapor deposition. The degree of vacuum during the deposition is 2.0 × 10 ⁻⁶ Torr (about
2.7 × 10 ⁻⁴ Pa), a deposition rate of 0.3 nm / sec, and a 20-nm-thick film formed of a hole-injecting layer 3 composed of polymer (3) and TBPAH.
And the hole transport layer 4 was completed.

[0103]

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Subsequently, as a material for the light emitting layer 5, 8-hydroxyquinoline complex of aluminum represented by the following structural formula: Al (C ₉ H ₆ NO) ₃ was deposited in the same manner as the hole transport layer 4. Crucible temperature of the aluminum 8-hydroxyquinoline complex in this procedure was controlled within the range of two hundred sixty-five to two hundred seventy-five ° C., vacuum degree during deposition was 1.5 × 10 ^-6 Torr (about 2.0 × 10 ^{- 4}
Pa), the deposition rate was 0.5 nm / sec, and the thickness of the deposited light-emitting layer 5 was 70 nm.

[0105]

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The substrate temperature during vacuum deposition of the hole transport layer 4 and the light emitting layer 5 was kept at room temperature.

Here, the element on which the light-emitting layer 5 was deposited was once taken out of the vacuum deposition apparatus into the atmosphere, and a 2 mm-wide striped shadow mask was used as a cathode deposition mask, and the ITO stripe of the anode 2 was used. And placed in another vacuum vapor deposition apparatus in the same manner as the organic layer, and the degree of vacuum in the apparatus is 2 × 10 ⁻⁶ Torr (approx.
Evacuation was performed until the pressure became 2.7 × 10 ⁻⁴ Pa) or less. After that, using magnesium and silver as a material of the cathode 7, a film is formed by a binary deposition method so that an atomic ratio of Mg: Ag = 10: 1, and the cathode 7 having a thickness of 200 nm is formed on the light emitting layer 5. Formed.

As described above, an organic electroluminescent device having a light emitting area of 2 mm × 2 mm was obtained. Table 3 shows the light emission characteristics of this device. This element has a voltage of 11V
Showed a high luminance of 5000 cd / m ² .

Example 2 An element was produced in the same manner as in Example 1, except that the polymer (5) obtained in Synthesis Example 2 was used instead of the polymer (3) as a material for the hole injection layer. Table 3 shows the emission characteristics of the obtained device.
It was shown to. As is clear from Table 3, a low operating voltage was obtained as in Example 1.

Example 3 An element was produced in the same manner as in Example 1 except that the polymer (6) obtained in Synthesis Example 2 was used instead of the polymer (3) as a material for the hole injection layer. Table 3 shows the emission characteristics of the obtained device.
It was shown to. As is clear from Table 3, a low operating voltage was obtained as in Example 1.

Comparative Example 1 An element was prepared in the same manner as in Example 1 except that the hole injection layer did not contain TBPAH. Table 3 shows the emission characteristics of the obtained element.

Comparative Example 2 An element was prepared in the same manner as in Example 2 except that the hole injection layer did not contain TBPAH. Table 3 shows the emission characteristics of the obtained element.

Comparative Example 3 An element was produced in the same manner as in Example 3 except that the hole injection layer did not contain TBPAH. Table 3 shows the light emission characteristics of the obtained element.

[0114]

[Table 3]

[0115]

As described in detail above, according to the organic electroluminescent device of the present invention in which a layer containing a specific fluorene-containing aromatic amine polymer and an electron accepting compound is formed, high light emission at a low voltage is obtained. An element which can be driven efficiently and has good heat resistance is provided.

Accordingly, the organic electroluminescent device according to the present invention can be used as a light source (for example, a light source of a copier, a liquid crystal display, or an instrument) utilizing the characteristics of a flat panel display (for example, for an OA computer or a wall-mounted television) or a surface light emitting body. It can be applied to various types of backlight sources, display boards, and marker lights, and has a great technical value especially as a display element for a vehicle that requires high heat resistance.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing an example of an embodiment of an organic electroluminescent device of the present invention.

FIG. 2 is a schematic sectional view showing another example of the embodiment of the organic electroluminescent device of the present invention.

FIG. 3 is a schematic sectional view showing another example of the embodiment of the organic electroluminescent device of the present invention.

FIG. 4 is an energy level diagram showing the relationship between ionization potential and electron affinity.

[Explanation of symbols]

 Reference Signs List 1 substrate 2 anode 3 hole injection layer 4 hole transport layer 5 light emitting layer 6 electron transport layer 7 cathode

Continued on the front page (72) Inventor Hiroaki Ohashi 5-3-48 Town Heights Jonan 203-5, Jonan, Yonezawa-shi, Yamagata (72) Inventor Yoshiharu Sato 1000 Kamoshida-cho, Aoba-ku, Aoba-ku, Yokohama, Kanagawa Prefecture Mitsubishi Chemical Corporation Yokohama 3K007 AB02 AB06 AB14 BA06 CA01 CB01 DA01 DB03 EB00 4J002 BC122 CM011 DA016 DD056 DD076 DF006 DK006 EN136 ET006 EZ006 FD202 FD206 GP00

Claims (5)

[Claims] 1. An organic electroluminescent device having an anode, a cathode, and a light emitting layer present between the two electrodes on a substrate, wherein a repeating unit represented by the following general formula (I) is provided between the light emitting layer and the anode. Unit and weight average molecular weight of 1,000 ~
An organic electroluminescent device comprising a layer containing 1,000,000 fluorene-containing aromatic amine polymer and an electron-accepting compound. Embedded image (Wherein, ring D and ring E each independently represent a benzene ring which may have a substituent, and R ¹ and R ² each independently represent a hydrogen atom, a halogen atom, an alkyl group, an aralkyl group, Alkenyl group, cyano group, amino group, acyl group, alkoxycarbonyl group, carboxyl group, alkoxy group, aryloxy group, alkylamino group, haloalkyl group, hydroxyl group, aromatic hydrocarbon ring group which may have a substituent Or Ar represents an aromatic heterocyclic group, and Ar represents an aromatic hydrocarbon ring group or an aromatic heterocyclic group which may have a substituent.) 2. The organic electroluminescent device according to claim 1, wherein the value obtained by subtracting the electron affinity of the electron-accepting compound from the ionization potential of the fluorene-containing aromatic amine polymer is 0.7 eV or less. . 3. The layer containing the fluorene-containing aromatic amine polymer and the electron-accepting compound, wherein the content of the electron-accepting compound in the layer containing the fluorene-containing aromatic amine polymer is 0.
The organic electroluminescent device according to claim 1, wherein the content is in a range of 1 to 50% by weight. 4. The organic electroluminescent device according to claim 1, wherein the electron accepting compound is represented by the following general formula (II). Embedded image (In the formula, X represents a halogen atom, and rings A, B, and C each independently represent a benzene ring which may have a substituent.) 5. The organic electroluminescent device according to claim 1, wherein the electron accepting compound is at least one selected from the following compound group. Embedded image