JP2003031371A - Organic electroluminescent element and blue light emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To fully ensure the drive stability of an element in an organic electroluminescent element and to provide the element with high color purity. SOLUTION: This organic electroluminescent element has a luminescent layer clamped between an anode and a cathode, on a substrate, and a hole blocking layer on the cathode side interface of the luminescent layer. The hole blocking layer contains a compound expressed by a general formula (I). In the formula (I), a carbozolyl group and a phenylene group may have an arbitrary substituent, and Z shows a divalent linkage group.

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 a blue light emitting device, and more particularly to a thin film type 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 electroluminescence (EL) element, ZnS and Ca which are II-VI group compound semiconductors of inorganic materials have been used.
For S, SrS, etc., the emission center of Mn and rare earth elements (Eu, Ce,
Tb, Sm, etc.) are generally doped, but EL devices made from the above inorganic materials have the following features: 1) AC drive is required (50 to 1000 Hz), 2) High drive voltage (up to 200 V), 3) It is difficult to realize full color (especially blue), and 4) the cost of the peripheral drive circuit is high.

However, in recent years, in order to improve the above problems,
Development of EL devices using organic thin films has started. In particular, in order to improve the light emission efficiency, the type of electrode was optimized for the purpose of improving the efficiency of carrier injection from the electrode, and a hole transport layer made of an aromatic diamine and a light emitting layer made of an aluminum complex of 8-hydroxyquinoline were formed. Development of organic electroluminescent device with the structure (Appl. Phys. Lett., 51, 9
(Pp. 13, 1987), the luminous efficiency is significantly improved as compared with the conventional EL element using a single crystal such as anthracene. In addition, for example, by using an aluminum complex of 8-hydroxyquinoline as a host material, doping a fluorescent dye for laser such as coumarin (J. Appl. Phys., Vol. 65,
(Page 3610, 1989), the emission efficiency has been improved and the emission wavelength has been converted.

In addition to the electroluminescent device using the low molecular weight material as described above, poly (p-phenylene vinylene), poly [2-methoxy-5- (2-ethylhexyloxy)- 1,4-phenylene vinylene], poly (3-alkylthiophene), and other electroluminescent devices, and devices in which polymers such as polyvinylcarbazole are mixed with low-molecular emitting materials and electron transfer materials Is also being developed.

One of the major problems in applying the organic electroluminescent device to the field of flat panel displays is improvement of driving stability. In particular, in an organic electroluminescence device formed by laminating a low molecular weight material, it is a problem that the life of a blue device is shorter than that of other emission colors. The blue light emitting element is required not only for the dot matrix type full-color display element that requires blue as a luminescent color but also for the white light emitting element, and the prolongation of its life is an essential issue in practical application.

Further, in terms of application to a small character display element, the simple matrix driving method is mainly adopted.
In this method, since the element is made to emit light at a high duty ratio in an extremely short time, it is advantageous for heat generated in the element, but it is necessary to make the element emit light at extremely high brightness, which promotes shortening of life. There is a problem.

In the organic electroluminescence devices reported so far, light emission is basically obtained by a combination of a hole transport layer and an electron transport layer. In this device, the holes injected from the anode move in the hole transport layer, and recombine with the electrons injected from the cathode and move in the electron transport layer in the vicinity of the interface between both layers. And / or the principle is to excite the electron transport layer to emit light. In recent years, an element in which a light emitting layer is provided between a hole transporting layer and an electron transporting layer to improve the light emission efficiency is general.

Further, a hole blocking layer is provided between the light emitting layer and the electron transporting layer for the purpose of promoting the generation of excitons in the light emitting layer and improving the efficiency of emission and the purification of emission color. There is. In particular, it is common in blue light emitting devices. With respect to these hole blocking layers, provided between the light emitting layer and the cathode,
As a hole blocking layer having an ionization potential larger than the ionization potential of the light emitting layer by 0.1 eV or more, tris (5,7-dichloro-8-hydroxyquinolino) aluminum (JP-A-2-195683) or silacyclo An element provided with a hole blocking layer made of pentadiene (Japanese Patent Laid-Open No. 9-87616) has been proposed, but the driving stability was not sufficient. As factors of this drive deterioration, thermal deterioration due to the low glass transition temperature (Tg) of the material, and electrochemical factors such that the material is reduced / oxidized by injection of electrons and holes are considered. There is.

In the organic electroluminescent device, in order to manufacture a device having high luminous efficiency and stability, electrons injected from the cathode are efficiently transported to the light emitting layer and holes passing through the light emitting layer are blocked. Therefore, further improvement studies have been desired for the element structure and materials for that purpose.

Incidentally, Japanese Unexamined Patent Publication (Kokai) No. 8-60144 discloses an organic electroluminescence device using a layer containing 4,4'-di (N-carbazolyl) biphenyl as a cathode interface layer. It is not described at all that the compound having a specific structure having a phenylcarbazole group has an excellent hole blocking action.

[0011]

The present invention is capable of efficiently transporting electrons injected from the cathode to the light emitting layer,
In addition, it has a hole blocking layer that can surely block holes passing through the light emitting layer and is excellent in heat deterioration and electrochemical stability. It is an object of the present invention to provide an organic electroluminescent device and a blue light emitting device which can emit light with high efficiency and have excellent driving stability.

[0012]

An organic electroluminescent device of the present invention has a light emitting layer sandwiched between an anode and a cathode on a substrate, and is in contact with an interface of the light emitting layer on the cathode side to block holes. In the organic electroluminescent device provided with a layer, the hole blocking layer contains a compound represented by the following general formula (I).

[0013]

[Chemical 7]

(In the formula, the carbazolyl group and the phenylene group may have arbitrary substituents, and the substituents may be bonded to each other to form a ring condensed with the carbazolyl group or the phenylene group. . Z represents a divalent linking group.)

The blue light emitting device of the present invention comprises such an organic electroluminescent device of the present invention.

That is, the present inventors have conducted extensive studies to achieve the above object, and as a result, found that the object of the present invention can be achieved by using the above-mentioned specific compound as the material of the hole blocking layer. The present invention has been completed.

The blue light emitting device of the present invention comprises such an organic electroluminescent device of the present invention.

The material constituting the hole blocking layer is an ionization potential of a substance that contributes to light emission in the light emitting layer (as will be described later, when the light emitting layer contains a host material and a dopant, the ionization of the host material is carried out). It is preferable to have an ionization potential larger than the potential) by 0.1 eV or more. Further, it is necessary that the compound has a stable thin film shape, has a high glass transition temperature (Tg), and can efficiently transport electrons. Further, it is required to be a compound that is electrochemically and chemically stable, and that impurities that become traps or quench light emission are unlikely to be generated during production or use.

A compound having an N-phenylcarbazole skeleton represented by the general formula (I) satisfies all such requirements, and thus emits a desired emission color with high color purity and high efficiency. In addition, it is possible to realize an organic electroluminescence device having excellent driving stability.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the organic electroluminescent device and the blue light emitting device of the present invention will be described in detail below.

First, the compound represented by the above general formula (I) which constitutes the hole blocking layer in the organic electroluminescent device of the present invention will be described.

The compound represented by the general formula (I) may have an arbitrary substituent on the carbazolyl group and / or the phenylene group, and the substituent is
If it does not adversely affect the basic characteristics of the present invention,
Any substituent may be used. Further, the substituents may form a ring.

The compound represented by the above general formula (I) is preferably represented by the following general formula (I ').

[0024]

[Chemical 8]

(In the formula (I '), R ^{1 to} R ¹⁶ are each independently a hydrogen atom, a halogen atom, an alkyl group, an aralkyl group, an alkenyl group, a cyano group, an amino group, an acyl group, an alkoxycarbonyl group or a carboxyl group. Group, an alkoxy group, an alkylamino group, an aralkylamino group, a haloalkyl group, a hydroxyl group, an aryloxy group, an optionally substituted aromatic hydrocarbon ring group or an aromatic heterocyclic group, R ¹ and R ² , R ³ and R ⁴ , R ⁵ and R ⁶ , R ⁷ and R ⁸ , R ⁹ and R ¹⁰ , R ¹¹ and R ¹² , R ¹³ and R ¹⁴ , R ¹⁵ and R ¹⁶ are bonded to form a ring. It may be formed. Z represents a divalent linking group.)

Specific examples of R ^{1 to} R ¹⁶ in the formula (I ') are hydrogen atom; halogen atom such as chlorine atom and fluorine atom; alkyl group having 1 to 6 carbon atoms such as methyl group and ethyl group; Aralkyl group such as benzyl group; alkenyl group having 2 to 6 carbon atoms such as vinyl group; cyano group; amino group; acyl group; alkoxycarbonyl group having 2 to 6 carbon atoms such as methoxycarbonyl group and ethoxycarbonyl group; carboxyl group An alkoxy group having 1 to 6 carbon atoms such as a methoxy group or an ethoxy group; a dialkylamino group such as a diethylamino group or a diisopropylamino group; a diaralkylamino group such as a dibenzylamino group or a diphenethylamino group; a trifluoromethyl group or the like Α-haloalkyl group; hydroxyl group; aryloxy group such as phenoxy group and benzyloxy group; Group, an aromatic hydrocarbon ring group such as a naphthyl group; an optionally substituted thienyl group, an aromatic heterocyclic group such as pyridyl group.

The substituents which the aromatic hydrocarbon ring group and aromatic heterocyclic group may have include halogen atoms such as fluorine atom; alkyl groups having 1 to 6 carbon atoms such as methyl group and ethyl group; vinyl group. An alkenyl group having 2 to 6 carbon atoms such as; a carbon number 2 such as a methoxycarbonyl group and an ethoxycarbonyl group
~ 6 alkoxycarbonyl group; C1-6 alkoxy group such as methoxy group, ethoxy group; aryloxy group such as phenoxy group, benzyloxy group; alkylamino group such as dimethylamino group, diethylamino group; acetyl group, etc. An acyl group; a haloalkyl group such as a trifluoromethyl group; and a cyano group.

R ¹ and R ² , R ³ and R ⁴ , R ⁵ and R
⁶ , R ⁷ and R ⁸ , R ⁹ and R ¹⁰ , R ¹¹ and R ¹² , R ¹³ and R
¹⁴ , R ¹⁵ and R ¹⁶ may be bonded to each other to form a 5- to 7-membered ring such as a benzene ring and a cyclohexane ring.

Particularly preferred as R ¹ to R ¹⁶ are
It is a hydrogen atom, an alkyl group, or a cyano group.

As Z in the general formula (I) or (I '), preferably a linking group shown below,

[Chemical 9] Examples thereof include a divalent aromatic hydrocarbon ring group or aromatic heterocyclic group which may have a substituent, or one of the following linking groups.

[0031]

[Chemical 10]

(The benzene ring portion in the above structure may have any substituent, and Ar ^{1 to} Ar ⁶ may have an aromatic hydrocarbon ring group or aromatic group which may have a substituent. Group heterocyclic groups or groups represented by the following general formula (II) can be given.

[Chemical 11] In addition, the carbazolyl group and the phenylene group in the formula (II) may have an arbitrary substituent. )

The aromatic hydrocarbon ring group of Z in the general formula (I) or (I ') is, for example, a phenylene group, a naphthylene group, an anthracene group, a naphthacene group or the like, a 5- or 6-membered monocycle or 2 to 6-membered ring. 4 condensed rings are mentioned. As the aromatic heterocyclic group for Z, for example, a thiophene group, a furan group, a pyridine group, a pyrimidine group, a quinoline group and the like, a 5- or 6-membered monocyclic ring or a 2-3 condensed ring can be mentioned.

Any of these aromatic hydrocarbon ring groups and aromatic heterocyclic groups may have a substituent, and the substituent may be, for example, a methyl group, an ethyl group or the like having 1 to 10 carbon atoms.
Examples thereof include a C6 alkyl group, a halogen atom such as a fluorine atom, and a C1-C6 α-haloalkyl group such as a trifluoromethyl group.

Ar ^{1 to} Ar ⁶ are aromatic hydrocarbon ring groups such as phenyl group, naphthyl group, anthranyl group, naphthacene group and the like, which are 5- or 6-membered monocyclic rings or 2 to 4 condensed rings, and thienyl groups. , A furyl group, a pyridyl group, a pyrimidyl group, a quinolyl group, or a 5- or 6-membered monocycle or 2
˜3 condensed ring aromatic heterocyclic groups. Each of these has a substituent such as an alkyl group having 1 to 6 carbon atoms such as a methyl group and an ethyl group, a halogen atom such as a fluorine atom, and an α-haloalkyl group having a carbon number of 1 to 6 such as a trifluoromethyl group. You can do it.

Z in the general formula (I) or (I ')
Is more preferably a phenylene group which may have a substituent, a naphthylene group, an anthracene group, a thiophene group, a furan group, or any of the following linking groups, from the viewpoint of hole blocking property. .

[0037]

[Chemical 12]

(The benzene ring portion in each of the above structures may have an arbitrary substituent, and Ar ³ to
Ar ⁶ is an aromatic hydrocarbon ring group or an aromatic heterocyclic group which may have a substituent, or a compound represented by the following formula (II)

[Chemical 13] Is one of the groups represented by. In addition, the carbazolyl group and the phenylene group in the formula (II) may have an arbitrary substituent. )

Further, the structure represented by the formula (II) is preferably represented by the following formula (II ').

[0040]

[Chemical 14]

(In the formula (II '), R ^{17 to} R ²⁴ are each independently a hydrogen atom, a halogen atom, an alkyl group, an aralkyl group, an alkenyl group, a cyano group or an amino group which may have a substituent. , An acyl group, an alkoxycarbonyl group, a carboxyl group, an alkoxy group, an alkylamino group, an aralkylamino group, a haloalkyl group, a hydroxyl group, an aryloxy group, an aromatic hydrocarbon ring group which may have a substituent or an aromatic heterocycle. Represents a ring group, R ¹⁷ and R ¹⁸ , R ¹⁹ and R ²⁰ ,
R ²¹ and R ²² , and R ²³ and R ²⁴ may form a ring with adjacent substituents. )

In the above formula (II '), R ^{17 to} R ²⁴ are specifically hydrogen atom; halogen atom; methyl group;
C1-C6 alkyl group such as ethyl group; aralkyl group such as benzyl group; C2-C6 alkenyl group such as vinyl group; cyano group; amino group; acyl group; methoxycarbonyl group, ethoxycarbonyl group, etc. An alkoxycarbonyl group having 2 to 6 carbon atoms; a carboxyl group; an alkoxy group having 1 to 6 carbon atoms such as a methoxy group and an ethoxy group; a dialkylamino group such as a diethylamino group and a diisopropylamino group; a dibenzylamino group, diphenethylamino Groups such as diaralkylamino group; α-such as trifluoromethyl group
Haloalkyl group; Hydroxyl group; Aryloxy group such as phenoxy group and benzyloxy group; Aromatic hydrocarbon ring group such as phenyl group and naphthyl group which may have a substituent; Thienyl which may have a substituent Group, and an aromatic heterocyclic group such as a pyridyl group.

The substituents that the aromatic hydrocarbon ring group and the aromatic heterocyclic group may have include 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; a vinyl group. An alkenyl group having 2 to 6 carbon atoms such as; a carbon number 2 such as a methoxycarbonyl group and an ethoxycarbonyl group
~ 6 alkoxycarbonyl group; methoxy group, ethoxy group, and other C1-6 alkoxy groups; phenoxy group, benzyloxy group, and other aryloxy groups; dimethylamino group, diethylamino group, and other dialkylamino groups, acetyl group, etc. An acyl group; a haloalkyl group such as a trifluoromethyl group; and a cyano group.

R ¹⁷ and R ¹⁸ , R ¹⁹ and R ²⁰ , R ²¹ and R ²² , R ²³ and R ²⁴ may be bonded to each other to form a 5- to 7-membered ring such as a benzene ring or a cyclohexane ring. Good.

Particularly preferred as R ¹⁷ to R ²⁴ are
It is a hydrogen atom, an alkyl group, or a cyano group.

Preferred specific examples of the compound represented by the above general formula (I) are shown below, but the invention is not limited thereto.

[0047]

[Chemical 15]

[0048]

[Chemical 16]

[0049]

[Chemical 17]

[0050]

[Chemical 18]

[0051]

[Chemical 19]

[0052]

[Chemical 20]

[0053]

[Chemical 21]

[0054]

[Chemical formula 22]

[0055]

[Chemical formula 23]

[0056]

[Chemical formula 24]

[0057]

[Chemical 25]

[0058]

[Chemical formula 26]

The structure of the organic electroluminescent device of the present invention will be described below with reference to the drawings.

1 to 3 are cross-sectional views schematically showing an embodiment of the organic electroluminescence device of the present invention, in which 1 is a substrate, 2 is an anode, 3 is an anode buffer layer, 4 is a hole transport layer, Reference numeral 5 is a light emitting layer, 6 is a hole blocking layer, 7 is an electron transport layer, and 8 is a cathode.

The substrate 1 serves as a support for the organic electroluminescent device, and a plate of quartz or glass, a metal plate or metal foil, a plastic film or sheet, etc. is used. In particular, a glass plate and a transparent synthetic resin plate such as polyester, polymethacrylate, polycarbonate, and polysulfone are preferable. When using a synthetic resin substrate, it is necessary to pay attention to the gas barrier property. If the gas barrier property of the substrate is too small, the organic electroluminescent element may deteriorate due to the outside air passing through the substrate, which is not preferable. Therefore, a method of providing a dense silicon oxide film or the like on at least one surface of the synthetic resin substrate to secure the gas barrier property is also a preferable method.

An anode 2 is provided on the substrate 1. Anode 2
Plays a role of injecting holes into the hole transport layer 4. This anode 2 is usually a metal such as aluminum, gold, silver, nickel, palladium, platinum, indium and / or
Alternatively, a metal oxide such as tin oxide, a metal halide such as copper iodide, carbon black, or a conductive polymer such as poly (3-methylthiophene), polypyrrole, or polyaniline is used. The anode 2 is usually formed by a sputtering method, a vacuum vapor deposition method, or the like. When fine particles of metal such as silver, fine particles of copper iodide, carbon black, fine particles of conductive metal oxide, fine particles of conductive polymer, etc. are used, they are dispersed in an appropriate binder resin solution and then the substrate 1 The anode 2 can also be formed by applying the composition onto the anode 2. Further, in the case of a conductive polymer, a thin film can be formed directly on the substrate 1 by electrolytic polymerization, or a conductive polymer can be applied on the substrate 1 to form the anode 2 (Appl. Phys. Lett. ． 、 60
Vol. 2711, 1992).

The anode 2 may have a laminated structure formed by laminating layers made of different materials.

The thickness of the anode 2 depends on the transparency required. When transparency is required, the visible light transmittance is usually 60% or more, preferably 80% or more, and in this case, the thickness is usually 5 to 1000 nm, preferably 10 to It is about 500 nm. When the anode 2 may be opaque, the thickness of the anode 2 may be the same as that of the substrate 1. Further, it is also possible to stack different conductive materials on the anode 2.

A hole transport layer 4 is provided on the anode 2. The conditions required for the material of the hole transport layer 4 include 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 low, the transparency to visible light is high, the hole mobility is high, the stability is excellent, and impurities that serve as traps are less likely to be generated during manufacturing or use. Required.
Further, it is required that the light emitted from the light emitting layer 5 is not quenched because it is in contact with the light emitting layer 5 or that the efficiency is not lowered by forming an exciplex with the light emitting layer 5. In addition to the above general requirements, when considering application for in-vehicle display, the element is required to have further heat resistance, and therefore, a material having a Tg value of 85 ° C. or higher is desirable.

As such a hole transport material, for example, 4,4′-bis [N- (1-naphthyl) -N-phenylamino]
Contains two or more tertiary amines represented by biphenyl 2
Aromatic diamine in which one or more fused aromatic rings are substituted with nitrogen atoms (Japanese Patent Laid-Open No. 5-234681), 4,4 ', 4 "-tris (1-
Aromatic amine compounds with a starburst structure such as naphthylphenylamino) triphenylamine (J. Lumi
n., 72-74, 985, 1997), an aromatic amine compound consisting of a tetramer of triphenylamine (Chem.Commun., 21.
75, 1996), 2,2 ', 7,7'-tetrakis- (diphenylamino) -9,9'-spirobifluorene and other spiro compounds (Syn
th. Metals, 91, 209, 1997).
These compounds may be used alone, or may be used as a mixture if necessary.

In addition to the above compounds, as a material for the hole transport layer 4, polyvinylcarbazole, polyvinyltriphenylamine (JP-A-7-53953), and polyarylene ether sulfone containing tetraphenylbenzidine (Polym. Adv. Tech., Vol. 7, p. 33, 1996).

When the hole transport layer 4 is formed by a coating method,
If necessary, an additive such as a binder resin or a coatability improving agent that does not become a hole trap is added to one or more hole transport materials, and the mixture is dissolved to prepare a coating solution. The positive electrode 2 is coated by a method and dried to form the hole transport layer 4. As a binder resin,
Examples thereof include polycarbonate, polyarylate, polyester and the like. The addition amount of the binder resin decreases the hole mobility when it is added in a large amount. Therefore, the addition amount of the binder resin is preferably as small as possible.

When the hole transport layer 4 is formed by the vacuum deposition method, the hole transport material is put in a crucible installed in a vacuum container, and the inside of the vacuum container is adjusted to about 10 ⁻⁴ Pa by an appropriate vacuum pump. After evacuation to, the crucible is heated to evaporate the hole transport material and form the hole transport layer 4 on the substrate 1 on which the anode 2 is formed, facing the crucible.

The thickness of the hole transport layer 4 is usually 5 to 300 nm,
It is preferably 10 to 100 nm. In order to uniformly form such a thin film, the vacuum evaporation method is often used.

A light emitting layer 5 is provided on the hole transport layer 4. The light-emitting layer 5 has a structure in which, between the electrodes to which an electric field is applied, holes that are injected from the anode 2 and move in the hole transport layer 4 and electrons that are injected from the cathode 8 and move in the hole blocking layer 6 are regenerated. It is formed of a fluorescent compound that is excited by the bond and emits strong light.

The fluorescent compound used for the light emitting layer 5 is a compound having a stable thin film shape, showing a high fluorescence yield in a solid state, and capable of efficiently transporting holes and / or electrons. It is necessary. Further, it is required to be a compound that is electrochemically and chemically stable and that is less likely to generate impurities that serve as traps during production or use.

As a material satisfying such a condition, 8-
Metal complex such as aluminum complex of hydroxyquinoline (JP-A-59-194393), 10-hydroxybenzo [h]
Metal complexes of quinoline (JP-A-6-322362), bisstyrylbenzene derivatives (JP-A1-245087, JP-A-2-2287)
2484), a bisstyrylarylene derivative (JP
2-247278), metal complexes of (2-hydroxyphenyl) benzothiazole (JP-A-8-315983), silole derivatives and the like. Further, among the hole transport layer materials described above, an aromatic amine compound having fluorescence can also be used as the light emitting layer material.

These light emitting layer materials are usually laminated on the hole transport layer by a vacuum vapor deposition method to form the light emitting layer 5.

The thickness of the light emitting layer 5 is usually 3 to 200 nm, preferably 5 to 100 nm.

The light emitting layer can be formed in the same manner as the hole transporting layer, but the vacuum deposition method is usually used.

For the purpose of improving the light emission efficiency of the device and changing the light emission color, for example, doping a fluorescent dye for laser such as coumarin with aluminum complex of 8-hydroxyquinoline as a host material (J. Appl. Phys. , 65
Vol. 3610, 1989). This doping method can also be applied to the light emitting layer 5, and various fluorescent dyes other than coumarin can be used as the doping material in this case. Examples of fluorescent dyes that emit blue light include perylene, pyrene, anthracene, coumarin, and derivatives thereof. Examples of the green fluorescent dye include quinacridone derivatives and coumarin derivatives. Examples of yellow fluorescent dyes include rubrene and perimidone derivatives. Examples of red fluorescent dyes include DCM compounds, benzopyran derivatives, rhodamine derivatives, benzothioxanthene derivatives, azabenzothioxanthene, and the like.

Besides the above-mentioned fluorescent dyes for doping, depending on the host material, Laser Research, Vol. 8, page 694, page 803, 958
Pp. (1980); Vol. 9, p. 85 (1981), the fluorescent dyes can be used as a doping material for the light emitting layer.

The amount of the fluorescent dye doped with respect to the host material is preferably 10 ⁻³ to 10% by weight.

A method of doping the above-mentioned fluorescent dye into the host material of the light emitting layer will be described below.

When the light-emitting layer is formed by a coating method, the above-mentioned light-emitting layer host material, a fluorescent dye for doping, and optionally a binder resin which does not become an electron trap or a quencher of light emission, a leveling agent, etc. are improved in coatability. An additive such as an agent is added to prepare a dissolved coating solution, which is coated on the hole transport layer 4 by a method such as a spin coating method and dried to form the light emitting layer 5. Examples of the binder resin include polycarbonate, polyarylate, polyester and the like. If the addition amount of the binder resin is large, the hole / electron mobility is lowered.
The content thereof is preferably 50% by weight or less.

When the light emitting layer is formed by the vacuum vapor deposition method,
Put the host material in the crucible installed in the vacuum container, put the fluorescent dye to be doped in another crucible, after evacuating the vacuum container to about 10 ^-4 Pa with a suitable vacuum pump,
Each crucible is simultaneously heated and evaporated to form a layer on the hole transport layer 4 of the substrate placed facing the crucible. As another method, a mixture of the above materials in a predetermined ratio may be put in the same crucible and evaporated.

When each of the above dopants is doped in the light emitting layer 5, it is usually doped uniformly in the thickness direction of the light emitting layer 5, but there may be a concentration distribution in the thickness direction. For example, it may be doped only near the interface with the hole transport layer 4, or conversely, may be doped only near the interface with the hole blocking layer 6.

The hole blocking layer 6 is formed on the light emitting layer 5 and then on the light emitting layer 5.
Is laminated so as to be in contact with the interface on the cathode side of. The hole blocking layer 6 has a role of blocking the holes moving from the hole transport layer 4 from reaching the cathode 8, and also efficiently transports electrons injected from the cathode 8 toward the light emitting layer 5. Is formed from a compound capable of. The physical properties required for the material forming the hole blocking layer 6 are high electron mobility and low hole mobility. The hole blocking layer 6 has a function of confining holes and electrons in the light emitting layer 5 to improve the light emission efficiency. Therefore, the ionization potential of the hole blocking layer 6 is 0 than the ionization potential of the light emitting layer 5. Greater than 1 eV is desired.

In the present invention, the compound represented by the general formula (I) is used as the material of the hole blocking layer 6, but these compounds may be used alone in the hole blocking layer 6. Of course, if necessary, two or more kinds may be mixed and used. The hole blocking layer is preferably composed only of the compound represented by the general formula (I).
It may contain a substance other than the compound represented by. In this case, in order to surely obtain the effect of the present invention, the hole blocking layer 6
The content of the compound represented by the general formula (I) in the
It is preferably not less than 80% by weight, more preferably not less than 80% by weight, and most preferably substantially composed of the compound represented by formula (I).

The thickness of the hole blocking layer 6 is usually 0.3 to 100 n.
m, preferably 0.5-50 nm.

The hole blocking layer 6 can be formed by the same method as the hole transporting layer 4, but a vacuum deposition method is usually used.

The cathode 8 has the hole blocking layer 6 and the light emitting layer 5
Plays a role of injecting electrons into. The material used for the cathode 8 may be the material used for the anode 2, but a metal having a low work function is preferable for efficient electron injection, and tin, magnesium, indium, calcium, Suitable metals such as aluminum and silver or alloys thereof are used. Specific examples thereof include low work function alloy electrodes such as magnesium-silver alloy, magnesium-indium alloy, and aluminum-lithium alloy.

The film thickness of the cathode 8 is usually the same as that of the anode 2.

For the purpose of protecting the cathode made of a low work function metal, it is preferable to further stack a metal layer having a high work function and stable to the atmosphere on the cathode in order to increase the stability of the device. Metals such as aluminum, silver, copper, nickel, chromium, gold and platinum are used for this purpose.

For the purpose of further improving the luminous efficiency of the device, it is conceivable to provide an electron transport layer 7 between the hole blocking layer 6 and the cathode 8 as shown in FIG. The electron transport layer 7 is formed of a compound capable of efficiently transporting electrons injected from the cathode 8 toward the hole blocking layer 6 between the electrodes to which an electric field is applied.

Therefore, as the electron-transporting compound used in the electron-transporting layer 7, the efficiency of electron injection from the cathode 8 is high, and the injected electron having a high electron mobility can be efficiently transported. It must be a compound.

As a material satisfying such a condition, 8
-A metal complex such as an aluminum complex of hydroxyquinoline (JP-A-59-194393), 10-hydroxybenzo
[h] Metal complexes of quinoline, oxadiazole derivatives, distyrylbiphenyl derivatives, silole derivatives, 3-or
5-hydroxyflavone metal complex, benzoxazole metal complex, benzothiazole metal complex, trisbenzimidazolylbenzene (US Pat. No. 5,645,948), quinoxaline compound (JP-A-6-207169), phenanthroline derivative (JP-A-5-331459). Gazette), 2-t-butyl
-9,10-N, N'-dicyanoanthraquinone diimine, n-type hydrogenated amorphous silicon carbide, n-type zinc sulfide, n-type zinc selenide and the like can be mentioned.

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

The electron transport layer 7 is formed by laminating on the hole transport layer 6 by a coating method or a vacuum deposition method in the same manner as the hole transport layer 4. Usually, a vacuum vapor deposition method is used.

Further, the efficiency of hole injection is further improved,
In addition, for the purpose of improving the adhesion of the entire organic layer to the anode 2, as shown in FIG. 3, the anode buffer layer 3 is inserted between the hole transport layer 4 and the anode 2. By inserting the anode buffer layer 3, it is possible to obtain an effect that the driving voltage of the element in the initial stage is lowered and, at the same time, an increase in voltage when the element is continuously driven with a constant current is suppressed. The conditions required for the material used for the anode buffer layer 3 are good contact with the anode 2, a uniform thin film can be formed, and thermal stability,
That is, the melting point and the glass transition temperature are high, and the melting point is preferably 300 ° C or higher, and the glass transition temperature is preferably 100 ° C or higher. Further, it has a low ionization potential, easy hole injection from the anode 2, and high hole mobility.

For this purpose, phthalocyanine compounds such as copper phthalocyanine (JP 63-295695 A), polyaniline (Appl. Phys. Lett., Volume 64, 124)
P. 5, 1994), Polythiophene (Optical Materials, 9
Vol., P. 125, 1998), organic compounds, sputtered carbon films (Synth. Met., Vol. 91, p. 73, 1997), metal oxides such as vanadium oxide, ruthenium oxide, molybdenum oxide. Material (J. Phys. D, 29, 2750, 1996)
Has been reported.

The anode buffer layer 3 can also be formed into a thin film in the same manner as the hole transport layer 4, but in the case of an inorganic material, a sputtering method, an electron beam evaporation method or a plasma CVD method is further used.

The thickness of the anode buffer layer 3 formed as described above is usually 3 to 100 nm, preferably 5 to 50 nm.

Further, by inserting an ultrathin insulating film (film thickness 0.1 to 5 nm) of LiF, MgF ₂ , Li ₂ O or the like at the interface between the cathode 8 and the light emitting layer 5 or the electron transport layer 7, it is possible to improve the efficiency of the device. (Appl. Phys. Lett., 70, 152)
Page, 1997; Japanese Patent Laid-Open No. 10-74586; IEEE Trans. Elec
tron. DeVices, 44, 1245, 1997).

It should be noted that the structure opposite to that shown in FIG. 1, that is, the cathode 8, the hole blocking layer 6, the light emitting layer 5, the hole transport layer 4, is formed on the substrate.
It is also possible to stack the anodes 2 in this order, and as described above, it is also possible to provide the organic electroluminescent element of the present invention between two substrates, at least one of which is highly transparent. Similarly, it is also possible to stack in a structure opposite to the above-mentioned layer structure shown in FIGS. 2 and 3. Further, in addition to the layers shown in FIGS. 1, 2 and 3, any layer may be provided between the anode or the cathode and the light emitting layer.

The present invention can be applied to any organic electroluminescent device, including a single device, a device having a structure arranged in an array, and a structure having an anode and a cathode arranged in an XY matrix. You can

According to the organic electroluminescent element of the present invention, the hole blocking layer contains a compound having a specific N-phenylcarbazole skeleton, whereby the color purity is good and the driving stability is greatly improved. A device having luminous efficiency can be obtained. According to the present invention, a blue light emitting device, which has been difficult to achieve in the past, can be obtained as a device having excellent stability. Therefore, excellent performance can be exhibited in application to a full-color or multi-color panel.

[0104]

EXAMPLES Next, the present invention will be described more specifically by way of examples, but the present invention is not limited to the description of the following examples unless it exceeds the gist.

Example 1 An organic electroluminescent device having the structure shown in FIG. 3 was produced by the following method.

An indium tin oxide (ITO) transparent conductive film deposited to a thickness of 150 nm on a glass substrate 1 (manufactured by Geomatec; electron beam film-formed product; sheet resistance 15 Ω) was subjected to ordinary photolithography and hydrochloric acid etching. 2
The anode 2 was formed by patterning into a stripe having a width of mm. The patterned ITO substrate is cleaned in the order of ultrasonic cleaning with acetone, pure water, and ultrasonic cleaning with isopropyl alcohol, and then dried by nitrogen blow.
Finally, ultraviolet ozone cleaning was performed and the device was installed in a vacuum vapor deposition device. After rough evacuation of the above equipment with an oil rotary pump, use an oil diffusion pump equipped with a liquid nitrogen trap until the degree of vacuum inside the equipment becomes 2 x 10 ^-6 Torr (about 2.7 x 10 ^-4 Pa) or less. Exhausted.

Next, the following copper phthalocyanine (the crystal form is β type) placed in a molybdenum boat arranged in the above apparatus is heated to a vacuum degree of 1.7 × 10 ⁻⁶ Torr (about 2.3 × 10 ⁶ ).
^-4 Pa), deposition rate is 0.14 nm / sec, deposition is 10 nm
The anode buffer layer 3 was formed.

[0108]

[Chemical 27]

Next, the following 4,4′-bis [N- (1-naphthyl) -N-phenylamino] biphenyl, placed in a ceramic crucible placed in the above apparatus, was tantalum around the crucible. Vapor deposition was performed by heating with a line heater. The temperature of the crucible at this time was controlled in the range of 245 to 260 ° C. The degree of vacuum during vapor deposition was 1.3 × 10 ⁻⁶ Torr (about 1.7 × 10 ⁻⁴ Pa) and the vapor deposition rate was 0.24 nm / sec.

[0110]

[Chemical 28]

Subsequently, as materials for the light emitting layer 5, a triphenylamine derivative (EM-1) having the structural formula shown below and a coumarin derivative (DYE-1) of a blue fluorescent dye are provided on the hole transport layer 4. Similarly, co-evaporation was performed at a ratio of 100: 1.
The temperature of the crucible at this time is 275-295 ℃, 193-198, respectively.
The temperature was controlled in the range of ° C. The degree of vacuum during vapor deposition is 1.1 × 10 ^-6 Torr
(About 1.5 × 10 ^-4 Pa), the deposition rate of EM-1 is 0.20 nm / sec,
A light emitting layer 5 having a film thickness of 30 nm was formed. The ionization potential of (EM-1) (the host compound of the light emitting layer 5) was 5.22, which was determined by using an atmospheric photoelectron spectrometer (AC-1) manufactured by Riken Keiki.
It was eV. Hereinafter, all the ionization potentials in the examples of the present application are values similarly determined.

[0112]

[Chemical 29]

[0113]

[Chemical 30]

Further, as the hole blocking layer 6, the exemplified compound (H-6) was laminated in a film thickness of 10 nm at a vapor deposition rate of 0.12 nm / sec.
The degree of vacuum during vapor deposition was 1.1 × 10 ^-6 Torr (about 1.5 × 10 ^-4 Pa). The ionization potential of the exemplified compound (H-6), which was determined in the same manner as the host compound of the light emitting layer 5, was 5.96 eV.

Then, on the hole blocking layer 6, an aluminum 8-hydroxyquinoline complex represented by the following structural formula, Al (C ₉ H ₆ NO) ₃ , was vapor-deposited in the same manner as the electron transport layer 7. At this time, the crucible temperature of the aluminum 8-hydroxyquinoline complex was controlled in the range of 295 to 305 ° C, the vacuum degree during vapor deposition was 8.0 × 10 ^-7 Torr (approximately 1.1 × 10 ^-4 Pa), and the vapor deposition rate was
The film thickness was 35 nm at 0.24 nm / sec.

[0116]

[Chemical 31]

The substrate temperature during vacuum deposition of the hole transport layer 4, the light emitting layer 5, the hole blocking layer 6 and the electron transport layer 7 was kept at room temperature.

Here, the element on which the electron transport layer 7 has been vapor-deposited is once taken out from the vacuum vapor deposition apparatus into the atmosphere, and a 2 mm wide striped shadow mask is used as a cathode vapor deposition mask on the ITO of the anode 2. Adhere to the element so that it is orthogonal to the stripe, and install it in another vacuum deposition device, and set the degree of vacuum in the device to 2.2 in the same way as when forming the organic layer.
The gas was evacuated to below × 10 ^-6 Torr (about 3.0 × 10 ^-4 Pa).

After that, as the cathode 8, first, lithium fluoride (LiF) was used in a molybdenum boat, and the deposition rate was 0.0
4 nm / sec, vacuum degree 4.1 × 10 ^-6 Torr (about 5.5 × 10 ^-4 Pa),
A film having a thickness of 0.5 nm was formed on the electron transport layer 7. Next, heat the aluminum in the same way with a molybdenum boat,
Deposition rate 0.41 nm / sec, vacuum degree 9.0 × 10 ^-6 Torr (about 1.2 × 10
^-3 Pa) to form an aluminum layer with a thickness of 100 nm and form a cathode 8
Was completed. The substrate temperature during the vapor deposition of the above-mentioned two-layer type cathode 8 was kept at room temperature.

As described above, an organic electroluminescent device having a light emitting area portion having a size of 2 mm × 2 mm was obtained. The light emission characteristics of this device are shown in Table 1. In Table 1, the luminous efficiency is a value at 100 cd / m ² , the luminance / current is the gradient of the luminance-current density characteristic, and the voltage is the value at 100 cd / m ² . Stability is 60% of initial brightness when driven by DC at a current density of 0.25 A / cm ^2.
It was evaluated from the ratio of luminance after 2 seconds. A brightness ratio (brightness after 60 seconds / initial brightness) of 0.98 or more was “excellent”, 0.90 or more and less than 0.98 was “good”, and less than 0.90 was “inferior”.

The maximum wavelength of the emission spectrum of the device is 473 nm.
And was identified as from a fluorescent dye (DYE-1).
In addition, there is almost no deterioration in brightness and the stability is excellent.

Comparative Example 1 A device was prepared in the same manner as in Example 1 except that the hole blocking layer was not provided and the thickness of the electron transport layer was 45 nm. In this device, the ionization potential of Al (C ₉ H ₆ NO) ₃ forming the electron transport layer 7 in contact with the light emitting layer instead of the hole blocking layer 6 was 5.41 eV. The light emission characteristics of this device are shown in Table 1.

The maximum wavelength of the emission spectrum of the device is 514 nm.
The desired blue luminescence was not obtained, and green luminescence was observed from the aluminum 8-hydroxyquinoline complex used as the electron transport layer.

Comparative Example 2 A device was prepared in the same manner as in Example 1 except that an 8-hydroxyquinoline complex of silanolaluminum represented by the following structural formula (ionization potential: 5.51 eV) was used as the hole blocking layer. The light emission characteristics of this device are shown in Table 1.

The maximum wavelength of the emission spectrum of the device is 473 nm.
As a result, the desired blue light emission was obtained, but the luminance deterioration was large and the driving stability was lacking.

[0126]

[Chemical 32]

Comparative Example 3 4,4'-N, N'-dicarbazolylbiphenyl shown in the following structural formula as a hole blocking layer (ionization potential: 5.93 eV)
A device was manufactured in the same manner as in Example 1 except that was used. The light emission characteristics of this device are shown in Table 1.

The maximum wavelength of the emission spectrum of the device is 524 nm.
The desired blue luminescence was not obtained, and green luminescence was observed from the aluminum 8-hydroxyquinoline complex used as the electron transport layer.

[0129]

[Chemical 33]

Example 2 A device was prepared in the same manner as in Example 1 except that the exemplified compound (H-25) was used as the hole blocking layer. The light emission characteristics of this device are shown in Table 1.

The maximum wavelength of the emission spectrum of the device is 471 nm.
The desired blue light emission was obtained, and the deterioration in luminance was small and the driving stability was good.

[0132]

[Table 1]

[0133]

As described in detail above, according to the organic electroluminescence device of the present invention, it is possible to obtain only light emission from a light emitting material arbitrarily selected, and further, light emission excellent in driving stability. Can be obtained. In particular, the improvement in driving stability of the blue light emitting element, which has been difficult in the past, is remarkable.

Therefore, the organic electroluminescent device according to the present invention is a light source (for example, a copying machine) that makes use of the characteristics of a flat panel display (for OA computer or wall-mounted television, for example), an on-vehicle display device, a mobile phone display, or a surface light emitter. Light sources, backlight sources for liquid crystal displays and measuring instruments), display boards, and marker lights, and their technical value is great.

[Brief description of drawings]

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

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

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

[Explanation of symbols]

1 substrate 2 anode 3 Anode buffer layer 4 Hole transport layer 5 Light emitting layer 6 Hole blocking layer 7 Electron transport layer 8 cathode

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Akiko Ichinozawa             1000 Kamoshida-cho, Aoba-ku, Yokohama-shi, Kanagawa             Within Mitsubishi Chemical Corporation F-term (reference) 3K007 AB04 AB06 AB11 BA06 CA01                       CB01 DA01 DB03 EB00

Claims (8)

[Claims] 1. An organic electroluminescent device comprising a substrate, a light emitting layer sandwiched between an anode and a cathode, and a hole blocking layer provided in contact with an interface of the light emitting layer on the cathode side. An organic electroluminescence device, wherein the hole blocking layer contains a compound represented by the following general formula (I). [Chemical 1] (In the formula (I), the carbazolyl group and the phenylene group may have an arbitrary substituent, and the substituents may be bonded to each other to form a ring condensed with the carbazolyl group or the phenylene group. . Z represents a divalent linking group.) 2. A compound represented by the general formula (I) is
It represents with General formula (I '), It is characterized by the above-mentioned.
The organic electroluminescent element as described. [Chemical 2] (In the formula (I '), R¹~ R¹⁶Are each independently a hydrogen atom,
Halogen atom, alkyl group, aralkyl group, alkenyl
Group, cyano group, amino group, acyl group, alkoxycarbo
Nyl group, carboxyl group, alkoxy group, alkylami
Group, aralkylamino group, haloalkyl group, hydroxyl group,
Aryloxy group, aromatic carbon which may have a substituent
Represents a hydrogenated ring group or an aromatic heterocyclic group, R¹And R², R
³And R^Four, R ^FiveAnd R⁶, R⁷And R⁸, R⁹And R^Ten, R¹¹When
R¹², R¹³And R¹⁴, R¹⁵And R¹⁶Are connected to form a ring
You may form. Z represents a divalent linking group. ) 3. Z in the general formula (I) or (I ′)
Is a linking group shown below, A divalent aromatic hydrocarbon ring group or aromatic heterocyclic group which may have a substituent, or the following linking group: (The benzene ring portion in each of the above structures may have any substituent, and in the formula, Ar ^{1 to} Ar ⁶ are aromatic hydrocarbon ring groups which may have a substituent. Or an aromatic heterocyclic group, or a compound represented by the following general formula (II) Is one of the groups represented by. In the formula (II), the carbazolyl group and the phenylene group may have any substituent. The organic electroluminescent element according to claim 1 or 2, which has a structure represented by any one of (1) to (3). 4. The organic electroluminescent device according to claim 3, wherein the structure represented by the general formula (II) is a structure represented by the following general formula (II ′). [Chemical 6] (In the formula (II ′), R ^{17 to} R ²⁴ are each independently a hydrogen atom,
Halogen atom, alkyl group, aralkyl group, alkenyl group, cyano group, optionally substituted amino group, acyl group, alkoxycarbonyl group, carboxyl group, alkoxy group, alkylamino group, aralkylamino group,
A haloalkyl group, a hydroxyl group, an aryloxy group, an aromatic hydrocarbon ring group which may have a substituent or an aromatic heterocyclic group, R ¹⁷ and R ¹⁸ , R ¹⁹ and R ²⁰ , R ²¹ and R ²² , R
²³ and R ²⁴ may combine with each other to form a ring. ) 5. The organic electroluminescent device according to claim 1, wherein the ionization potential of the hole blocking layer is larger than the ionization potential of the light emitting layer by 0.1 eV or more. 6. The organic electroluminescent device according to claim 1, further comprising an electron transport layer between the hole blocking layer and the cathode. 7. The organic electroluminescent device according to claim 1, further comprising a hole transport layer between the light emitting layer and the anode. 8. A blue light emitting device comprising the organic electroluminescent device according to claim 1.