JP2000003787A - Organic electroluminescent device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an element having high heat resistance and blue luminescence with satisfactory color purity by making a specified mixing ligand type metallic complex having a high melting point as a host material in a luminescent layer and doping aromatic amine compound in this host material. SOLUTION: An organic electroluminescent element is formed by holding a luminescent layer and an electron hole transport layer by an anode and a cathode on a substrate. In the luminescent layer, a mixing ligand metallic material shown by in formula I is made a host material. In the formula I, R1 to R6 show hydrogen atoms, halogen atoms, alkyl groups, aralkyl groups, aryl groups, cyano groups, amino groups, acyl groups, alkoxycarbonyl groups, killboxyl group, M represents Al or Ga atoms and L represents formula II or formula III. In the formulas II, III, Y is Si, Ge, Sn, and Ar1 to Ar4 are alkyl groups, aralkyl groups and alkenyl groups. In this host material, aromatic amine compound shown by a formula IV is included by 0.1 to 10 wt.%. In the formula IV, Ar5 to Ar7 show aromatic hydrocarbon ring groups and aromatic heterocyclic ring groups.

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 (50-1000 Hz), 2) High drive voltage (up to 200 V), 3) Full color is difficult (especially blue), 4) Peripheral drive circuit is expensive. I have.

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 provided with an electrode (Appl. Phys. Lett., 51
Vol., Pp. 913, 1987), the luminous efficiency has been greatly improved as compared with a conventional EL device using a single crystal such as anthracene. For example, doping a fluorescent dye for laser such as coumarin using an aluminum complex of 8-hydroxyquinoline as a host material (J. Appl. Phy.
s., 65, p. 3610, 1989), the improvement of luminous efficiency, conversion of luminous wavelength, and the like are also performed.

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] and poly (3-alkylthiophene), and devices in which a low molecular light emitting material and an electron transfer material are mixed with a polymer such as polyvinyl carbazole Is also being developed.

In order to apply the organic electroluminescent device to a display device such as a flat panel display, it is necessary to sufficiently secure the reliability of the device. However, the heat resistance of the conventional organic electroluminescent device is insufficient, and the current-voltage characteristic shifts to a higher voltage side due to an increase in the ambient temperature or process temperature of the device, or local Joule heat generated when the device is driven. Deterioration such as shortening of service life and generation and increase of non-light emitting portions (dark spots) was inevitable.

The main cause of the above-mentioned element deterioration is deterioration of the thin film shape of the organic layer. This deterioration of the thin film shape is caused by crystallization (or aggregation) of the organic amorphous thin film due to heat generated during driving of the element.
It is thought to be caused by such factors. This low heat resistance is considered to be due to the low glass transition temperature (hereinafter abbreviated as Tg) of the material. Tg generally has a linear correlation with the melting point. Further, regarding the blue light-emitting element, since many compounds used in the light-emitting layer have a small molecular weight and a low melting point and low Tg due to a restriction that pi electron conjugation cannot be expanded, it is possible to obtain an element having high heat resistance. Especially difficult. At present, it is not possible to obtain a material which is chemically stable enough.

[0007] Compounds that have been used in blue organic electroluminescent devices so far include anthracene, tetraphenylbutadiene, pentaphenylcyclopentadiene, distyrylbenzene derivatives, oxadiazole derivatives, azomethine zinc complexes, benzazole metal complexes (particularly Kaihei 8-8
No. 1472), mixed ligand type aluminum complex (J.SID,
5, p. 11, 1997), N, N'-diphenyl-N, N '-(3-
Methylphenyl) -1,1'-biphenyl-4,4'-diamine, polyvinylcarbazole, 1,2,4-triazole derivative, aminopyrene dimer, distyrylbiphenyl derivative (App
l. Phys. Lett., vol. 67, p. 3853, 1995), silole derivatives and the like. Among the above blue light-emitting materials, representative compounds whose device characteristics are well studied are shown below:

[0008]

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[0009]

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[0010]

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Distyrylbiphenyl derivative (B-1)
Has a strong fluorescence intensity and does not form an exciplex even when used in a device, and has been reported to emit blue light (Appl.
Phys. Lett., Vol. 67, p. 3853, 1995), the ionization potential in the thin film state is as high as 5.9 eV, and it is difficult for holes to be injected from the hole transport layer.
There is a problem that a broad peak having a light emission maximum is shown in the vicinity and the color purity of blue is not good. Bis (2-methyl-8
-Quinolinolato) (p-phenylphenolato) aluminum complex (B-2) also has insufficient blue color purity.

The aromatic diamine N, N'-diphenyl-
N, N '-(3-methylphenyl) -1,1'-biphenyl-4,4'-diamine (usually referred to as TPD) (B-3), when combined with a triazole derivative as a hole blocking layer Four
An EL spectrum having an emission peak at 64 nm is shown (Jp
n. J. Appl. Phys., 32, L917, 1993), TPD
Has a thermal instability such as crystallization because its Tg is as low as 63 ° C.

As described above, with respect to the blue light emitting element, 8-
At present, the stability of the device is further inferior to that of a green light-emitting device using an aluminum complex of hydroxyquinoline. As for the blue light emitting element, a doping method is being studied in the same manner as in the case of other colors in order to improve the luminous efficiency of the element and improve the durability.

As a blue fluorescent dye for doping, perylene and aromatic amine have been reported. Perylene is 470
It has been reported that blue light emission having a fluorescence maximum wavelength in nm and relatively good color purity is obtained by doping the host material (B-2). However, a longer wavelength due to concentration quenching and an increase in driving voltage are observed. However, the stability at the time of driving has not reached a practical level (Japanese Patent Laid-Open No. 5-198377). As for aromatic amines, distyrylbiphenyl derivatives (B-
It is disclosed that doping is carried out in 1) (Japanese Unexamined Patent Publication No.
As described above, this host material has a problem in element stability, especially heat resistance, because of its low melting point and low Tg.

For the above-mentioned reasons, the organic electroluminescent device has a large problem in terms of heat resistance of the device and, in the case of a blue light emitting device, color purity in practical use. The heat resistance and drive characteristics of the organic electroluminescent device are unstable,
The fact that the blue purity is not improved is an undesirable characteristic as a display element such as a flat panel display aiming at full color.

[0016]

SUMMARY OF THE INVENTION In view of the above situation, the present inventors have made intensive studies with the aim of providing an organic electroluminescent device having high heat resistance and exhibiting blue light emission with good color purity. As a result, it has been found that the above-mentioned problems can be solved by using a specific compound for the light-emitting layer of the organic electroluminescent device, and the present invention has been completed.

[0017]

That is, the gist of the present invention is an organic electroluminescent device including at least a light emitting layer sandwiched between an anode and a cathode on a substrate, wherein the light emitting layer has the following general formula (I) ) As a host material,

[0018]

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(Wherein R ^{1 to} R ⁶ are a hydrogen atom, a halogen atom, an alkyl group, an aralkyl group, an alkenyl group, an allyl group, a cyano group, an amino group, an acyl group, an alkoxycarbonyl group, a carboxyl group, an alkoxy group , An alkylsulfonyl group, an α-haloalkyl group, a hydroxyl group, an amide group which may have a substituent, an aromatic hydrocarbon ring group which may have a substituent or an aromatic which may have a substituent Represents a group heterocyclic group, M represents an Al atom or a Ga atom, and L is represented by any of the following general formulas (Ia) and (Ib).)

[0020]

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(Wherein, Y represents any atom of Si, Ge, and Sn, and Ar ^{1 to} Ar ⁴ represent an alkyl group, an aralkyl group, an alkenyl group, and an aromatic hydrocarbon which may have a substituent. Represents a hydrogen ring group or an aromatic heterocyclic group.) The aromatic amine compound represented by the following general formula (II) is
-10% by weight of the organic electroluminescent device.

[0022]

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(Wherein, Ar ^{5 to} Ar ⁷ each independently represent an aromatic hydrocarbon ring group or an aromatic heterocyclic group which may have a substituent, and at least one of Ar ^{5 to} Ar ⁷ One is selected from a fused aromatic ring group having 10 to 30 carbon atoms.)

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention improves the heat resistance of a device by using a metal complex having a high melting point as a host material of a light emitting layer, and at the same time, has an electron donating property and a high fluorescence quantum efficiency in a blue region. By doping the aromatic amine compound, the light emitting efficiency, blue color purity and driving voltage of the device can be reduced. Hereinafter, the organic electroluminescent device of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view schematically showing an example of the structure of a general organic electroluminescent device used in the present invention, wherein 1 is a substrate, 2 is an anode, 4 is a hole transport layer, 5 is a light emitting layer, and 7 is Each represents a cathode.

The substrate 1 serves as a support for the organic electroluminescent device, 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 small, the organic electroluminescent device may be deteriorated by the outside air passing through the substrate, which is not preferable. For this reason, a method of providing a dense silicon oxide film or the like on at least one surface of the synthetic resin substrate to secure gas barrier properties is also a preferable method.

An anode 2 is provided on the substrate 1, and the anode 2 plays a role of injecting holes into the hole transport layer. This 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; carbon black; (3-methylthiophene), conductive polymers such as polypyrrole and polyaniline. Usually, the formation of the anode 2 is often performed by a sputtering method, a vacuum evaporation method, or the like. In the case of fine metal particles such as silver, fine particles such as copper iodide, carbon black, conductive metal oxide fine particles, or conductive polymer fine powder, they are dispersed in a suitable binder resin solution and To form 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 the conductive polymer can be applied on the substrate 1 to form the anode 2 (Appl. Phys. Lett. 60, 2711,
1992). 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 5 to 1000 nm, preferably 10 to 10 nm. It is about 500 nm. If opaque, the anode 2 may be the same as the substrate 1. Further, it is also possible to laminate a different conductive material on the anode 2.

On the anode 2, a hole transport layer 4 is provided. As a condition required for the material of the hole transport layer, it is necessary that the material has a high hole injection efficiency from the anode and can efficiently transport 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, when considering applications for in-vehicle display, the element is required to have further heat resistance. Therefore, Tg is 85
A material having a value of at least C is desirable.

Examples of such a hole transporting material include 1,1-bis (4-di-p-tolylaminophenyl) cyclohexane and 4,4′-bis [N- (1-naphthyl) -N- Phenylamino] aromatic amines containing two or more tertiary amines represented by biphenyl and having two or more condensed aromatic rings substituted with nitrogen atoms (JP-A-5-234681), and derivatives of triphenylbenzene Aromatic triamines having a starburst structure (U.S. Pat. No. 4,923,774), N, N'-diphenyl-N, N'-bis (3-methylphenyl) biphenyl-4,4 '
-Compounds in which a pyrenyl group is substituted with a plurality of aromatic diamino groups, such as diamines; aromatic diamines having a styryl structure (JP-A-4-290851);
(Japanese Patent Application Laid-Open No. 4-304466) and a starburst type aromatic triamine (Japanese Patent Application Laid-Open No.
-308688), a tertiary amine linked by a fluorene group (JP-A-5-25473), a triamine compound (JP-A-5-239455), bisdipyridylaminobiphenyl, N, N, N-triamine Phenylamine derivatives (JP-A-6
-1972), an aromatic diamine having a phenoxazine structure (JP-A-7-138562), a diaminophenylphenanthridine derivative (JP-A-7-252474),
Examples thereof include silazane compounds (U.S. Pat. No. 4,950,950), silanamine derivatives (JP-A-6-49079), and phosphamine derivatives (JP-A-6-25659).
These compounds may be used alone, or may be used as a mixture as necessary.

In addition to the above compounds, materials for the hole transport layer 4 include polyvinyl carbazole, polysilane, polyphosphazene (JP-A-5-310949), polyamide (JP-A-5-310949), and polyvinyl triphenyl. Polymer materials such as amines (JP-A-7-53953), polymers having a triphenylamine skeleton (JP-A-4-1303065), and polymethacrylates containing aromatic amines are exemplified.

The hole transport layer 4 is formed by laminating the above hole transport material on the anode 2 by a coating method or a vacuum evaporation method. In the case of the coating method, one hole transport material is used.
A seed or two or more, and if necessary, an additive such as a binder resin or a coatability improver that does not trap holes are added and dissolved to prepare a coating solution, and the solution is formed on the anode 2 by a method such as spin coating. To the hole transport layer 3b
To form Examples of the binder resin include polycarbonate, polyarylate, and polyester. If the amount of the binder resin is large, the hole mobility is reduced, so that a small amount is desirable, and usually 50% by weight or less is preferable.

In the case of the vacuum vapor deposition method, the hole transporting material is put into a crucible placed 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 transport material is evaporated, and the hole transport layer 4 is formed on the substrate 1 on which the anode is formed, which is placed facing the crucible.
Is formed. The thickness of the hole transport layer 4 is usually 10 to 300 n
m, preferably 30-100 nm. In order to uniformly form such a thin film, generally, a vacuum deposition method is often used. The light emitting layer 5 is formed on the hole transport layer 4. The organic electroluminescent device of the present invention is characterized in that the light emitting layer contains the metal complex represented by the general formula (I) as a host material and the aromatic amine compound represented by the general formula (II) as a dope material. And

The general formula (I) represents a mixed ligand type metal complex, wherein R ^{1 to} R ⁶ each independently represent a hydrogen atom; a halogen atom such as a fluorine atom; a methyl group;
C1-C6 alkyl group such as ethyl group; cyclohexyl group; aralkyl group such as benzyl group and phenethyl group; alkenyl group such as vinyl group; C1-C6 alkoxycarbonyl group such as methoxycarbonyl group and 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; a dimethylamino group; a dialkylamino group such as a diethylamino group; an acyl group such as an acetyl group; A haloalkyl group such as a fluoromethyl group; a cyano group; an aromatic hydrocarbon ring group such as an optionally substituted phenyl group, a biphenyl group, a naphthyl group, an anthryl group, a phenanthryl group, a pyrenyl group; Carbazolyl, pyridyl, triazyl, pyrazyl, quinoxalyl , A thienyl group or other aromatic heterocyclic group; wherein the substituent is a halogen atom such as a fluorine atom; an alkyl group having 1 to 6 carbon atoms such as a methyl group or an ethyl group; an alkenyl group such as a vinyl group; An alkoxycarbonyl group having 1 to 6 carbon atoms, such as a methoxy group or an ethoxy group;
Aryloxy groups such as phenoxy group and benzyloxy group; dialkylamino groups such as dimethylamino group and diethylamino group; acyl groups such as acetyl group; haloalkyl groups such as trifluoromethyl group; and cyano group. . Particularly preferred examples of the substituent include a methyl group, a phenyl group, and a methoxy group.

M represents an Al atom or a Ga atom;
Is selected from the substituents represented by the general formulas (Ia) and (Ib), wherein Ar ^{1 to} Ar ⁴ each independently represent an alkyl having 1 to 6 carbon atoms such as a methyl group or an ethyl group. A cyclohexyl group; an aralkyl group such as a benzyl group or a phenethyl group; an alkenyl group such as a vinyl group; an aromatic hydrocarbon ring group or an aromatic heterocyclic group which may have a substituent, preferably phenyl. Group, a naphthyl group, a biphenyl group, an anthryl group, a thienyl group, a pyridyl group, and the like. As the substituent, a methyl group,
Examples include a methoxy group and a dimethylamino group. Y is Si
, Ge, or Sn. Specific examples of the metal complex represented by the general formula (I) are shown in Tables 1 and 2 below, but are not limited thereto.
As for R ^{1 to} R ⁶ , those not particularly shown in the table are hydrogen atoms.

[0034]

[Table 1]

[0035]

[Table 2]

[0036]

[Table 3]

Using the metal complex represented by the general formula (I) as a host material, the aromatic amine compound represented by the general formula (II) is doped. In the general formula (II), Ar ⁵ to Ar ⁷ are preferably a phenyl group, a biphenyl group, a naphthyl group, an anthryl group, a phenanthryl group, a pyrenyl group, a binaphthyl, each of which may independently have a substituent. Group, aromatic hydrocarbon ring group such as fluorenyl group; optionally substituted pyridyl group, triazyl group, pyrazyl group, quinoxalyl group, thienyl group, acridinyl group, phenazinyl group, phenanthridinyl group,
A substituent such as a halogen atom; an alkyl group having 1 to 6 carbon atoms such as a methyl group or an ethyl group; an alkenyl group such as a vinyl group; a methoxycarbonyl group; An alkoxycarbonyl group having 1 to 6 carbon atoms such as an ethoxycarbonyl group; a methoxy group;
An alkoxy group having 1 to 6 carbon atoms such as an ethoxy group; an aryloxy group such as a phenoxy group and a benzyloxy group; a dialkylamino group such as a diethylamino group and a diisopropylamino group. Particularly preferred examples of the substituent include a methyl group, a phenyl group and a methoxy group.
At least one of Ar ^{5 to} Ar ⁷ has 10 to 10 carbon atoms such as a naphthalene ring, anthracene ring, binaphthyl, fluorene ring, phenanthrene ring, pyrene ring, acridine ring, phenazine ring, phenanthridine ring, phenanthroline ring, bipyridyl ring and the like. Selected from 30 fused aromatic ring groups. Preferred specific examples of the compound represented by the general formula (II) are shown in Table 3 below, but are not limited thereto.

[0038]

[Table 4]

[0039]

[Table 5]

[0040]

[Table 6]

[0041]

[Table 7]

[0042]

[Table 8]

The amount of the aromatic amine compound doped in the light emitting layer is preferably in the range of 0.1 to 10% by weight.
If it is less than 0.1% by weight, there is no doping effect, no improvement in luminous efficiency, and no improvement in color purity. If it exceeds 10% by weight, the fluorescence quenching process due to the dimerization of the doped dyes or the formation of oligomers becomes dominant, and the luminous efficiency is greatly reduced. The thickness of the light emitting layer 5 is usually 10 to 200 nm, preferably
30-100 nm.

The light emitting layer 5 is formed by laminating on the hole transport layer 4 by a coating method or a vacuum evaporation method in the same manner as the hole transport layer 4. It is necessary to use a solvent that does not dissolve the existing hole transport layer. As a method of performing the above-mentioned doping by a vacuum evaporation method, there are a method of co-evaporation and a method of previously mixing an evaporation source at a predetermined concentration. When each of the above dopants is doped in the light emitting layer, the dopant is uniformly doped in the thickness direction of the light emitting layer, but may have a concentration distribution in the film thickness direction. For example, doping may be performed only near the interface with the hole transport layer, or conversely, doping may be performed near the cathode interface.

The cathode 7 plays a role of injecting electrons into the light emitting layer 5. The material used for the cathode 7 is the anode 2
It is possible to use a material used for the above, but for efficient electron injection, a metal having a low work function is preferable, and an appropriate metal such as tin, magnesium, indium, calcium, aluminum, silver or the like, An alloy 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. Further, LiF, MgF ₂ , Li ₂ O are provided at the interface between the cathode and the light emitting layer or the electron transport layer.
Inserting an ultra-thin insulating film (0.1 to 5 nm) such as is also an effective method to improve the efficiency of the device (Appl. Phys. Le
tt., 70, 152, 1997; Japanese Patent Application Laid-Open No. 10-74586; IEEE Trans. Electron. Devices, 44, 1245,
1997). The thickness of the cathode 7 is usually the same as that of the anode 2.
In order to protect the cathode made of a low work function metal, further laminating a metal layer having a high work function and being stable to the atmosphere increases the stability of the device. For this purpose, metals such as aluminum, silver, copper, nickel, chromium, gold, platinum and the like are used.

In the present invention, providing the electron transport layer 6 between the light emitting layer and the cathode as shown in FIG. 3 is very effective for improving the luminous efficiency of the device. Electron transport layer 6
Is formed of a compound capable of efficiently transporting electrons injected from the cathode between the electrodes to which an electric field is applied toward the light emitting layer 5 and efficiently performing recombination with holes. The electron transporting compound used in the electron transporting layer 6 is preferably a compound having high electron injection efficiency from the cathode 7 and having high electron mobility and capable of efficiently transporting injected electrons. is necessary.

Materials satisfying such conditions include 8
Metal complexes such as aluminum complexes of -hydroxyquinoline (JP-A-59-194393), 10-hydroxybenzo
[h] quinoline metal complex, oxadiazole derivative, distyrylbiphenyl derivative, silole derivative, 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. The thickness of the electron transport layer 6 is usually
It is 5 to 200 nm, preferably 10 to 100 nm. The electron transport layer 6 is laminated on the light-emitting layer 5 by a coating method or a vacuum deposition method in the same manner as the hole transport layer 4, but usually, a vacuum deposition method is used.

For the purpose of lowering the driving voltage of the device and improving the driving stability, as shown in FIG.
It is conceivable to provide the anode buffer layer 3 in order to improve the contact. The conditions required for the material used for the anode buffer layer are as follows: a uniform thin film can be formed with good contact with the anode and thermally stable, that is, the melting point and the glass transition temperature are high, and the melting point is 300 ° C. or higher, A glass transition temperature of 100 ° C or higher is required.
In addition, the ionization potential is low, holes can be easily injected from the anode, and the hole mobility is high. For this purpose, porphyrin derivatives and phthalocyanine compounds (JP-A-63-295695),
Starburst type aromatic triamine (JP-A-4-308688), hydrazone compound, alkoxy-substituted aromatic diamine derivative, p- (9-anthryl) -N, N-di-p-tolylaniline, polythienylenevinylene And organic compounds such as poly-p-phenylenevinylene and polyaniline, sputtered carbon films, and metal oxides such as vanadium oxide, ruthenium oxide and molybdenum oxide.

Examples of the compound often used as the material of the anode buffer layer include a porphyrin compound and a phthalocyanine compound. These compounds may have a central metal or may be non-metallic. Specific examples of preferred such compounds include the following compounds: porphine 5,10,15,20-tetraphenyl-21H, 23H-porphine 5,10,15,20-tetraphenyl-21H, 23H-porphine Cobalt (II) 5,10,15,20-Tetraphenyl-21H, 23H-porphine Copper (II) 5,10,15,20-Tetraphenyl-21H, 23H-porphine zinc (II) 5,10,15, 20-tetraphenyl-21H, 23H-porphine vanadium (IV) oxide 5,10,15,20-tetra (4-pyridyl) -21H, 23H-porphine 29H, 31H-phthalocyanine Copper (II) phthalocyanine Zinc (II) phthalocyanine Titanium phthalocyanine oxide Magnesium phthalocyanine Lead phthalocyanine Copper (II) 4,4 ', 4'',4'''-tetraaza-29H, 31H-phthalocyanine

In the case of the anode buffer layer, a thin film can be formed in the same manner as in the case of the hole transport layer. In the case of an inorganic substance, however, a sputtering method, an electron beam evaporation method,
Method is used. The thickness of the anode buffer layer 3 formed as described above is usually 3 to 100 nm, preferably 10 to 50 nm.
nm.

It is to be noted that the structure reverse to that of FIG. 1, that is, the cathode 7, the light emitting layer 5, the hole transport layer 4, and the anode 2 can be laminated in this order on the substrate, and at least one of the It is also possible to provide the organic electroluminescent device of the present invention between two substrates having high transparency. Similarly, it is also possible to laminate in a structure opposite to the above-mentioned respective layer constitutions shown in FIG. 2 and FIG.

According to the organic electroluminescent device of the present invention, a compound having a specific structure having a high melting point is used as a host of the light emitting layer, and a specific aromatic amine compound is doped in the host of the light emitting layer. Therefore, the heat resistance and luminous efficiency of the element are improved, and it is possible to obtain a blue light-emitting element with improved color purity and reduced driving voltage, which not only functions as a full-color or multi-color blue sub-pixel, but also functions as a fluorescent light. It is also possible to produce a full-color display element by combining with a conversion dye (Japanese Patent Laid-Open No.
-15,897).

[0053]

EXAMPLES Next, the present invention will be described more specifically with reference to 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 a structure shown in FIG. 2 was produced by the following method. A transparent conductive film of indium tin oxide (ITO) deposited on a glass substrate with a thickness of 120 nm (Geomatec Co., Ltd .; electron beam filmed product; sheet resistance of 15Ω) was fabricated using ordinary photolithography and hydrochloric acid etching.
An anode 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, water cleaning with pure water, and ultrasonic cleaning with isopropyl alcohol, dried with nitrogen blow, and finally cleaned with ultraviolet and ozone, and placed in a vacuum evaporation apparatus. installed. After performing rough exhaust of the above device by an oil rotary pump,
Evacuation was performed using an oil diffusion pump equipped with a liquid nitrogen trap until the degree of vacuum in the apparatus became 2 × 10 ⁻⁶ Torr (about 2.7 × 10 ⁻⁴ Pa) or less. The material of the hole transport layer 4 has the following structural formula

[0054]

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The 4,4'-bis [N- (1-naphthyl) -N-phenylamino] biphenyl (H-1) was placed in a ceramic crucible and heated by a tantalum wire heater around the crucible to perform vapor deposition. Was. At this time, the temperature of the crucible was controlled in the range of 240 to 260 ° C. The degree of vacuum during vapor deposition is 3.0 × 10 ⁻⁶ Torr (about 4.
(0 × 10 ⁻⁴ Pa), and a hole transport layer 4 having a thickness of 60 nm was obtained at a deposition rate of 0.4 nm / sec. Next, as a material of the light emitting layer 5, the following structural formula

[0056]

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Bis (2-methyl-8-quinolinolato) (triphenylsilanolato) aluminum complex (E
M-1) was used as a host, and the exemplary compound (III-25) was used as a doping material, and was stacked on the hole transport layer 4 by a co-evaporation method. At this time, the temperature of the crucible of (EM-1) was 240
The temperature of the crucible of Exemplified Compound (III-25) was controlled at 125 ° C. within the range of 250250 ° C. The degree of vacuum during deposition is 2.0 × 10 ^-6 To
rr (about 2.7 × 10 ^-4 Pa), a deposition rate of 0.2 nm / sec, and a film thickness of 30 nm. At this time, the amount of the exemplary compound (III-25) doped in the light emitting layer was 1.1% by weight.

[0058]

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Subsequently, as the material of the electron transport layer 6, an 8-hydroxyquinoline complex of aluminum (E-
1) was vapor-deposited on the light emitting layer in the same manner. At this time, the temperature of the crucible was controlled in the range of 280 to 290 ° C. The degree of vacuum during the deposition is 1.5 × 10 ⁻⁶ Torr (about 2.0 × 10 ⁻⁴ Pa),
The deposition rate was 0.3 nm / sec and the film thickness was 45 nm. The substrate temperature during vacuum deposition of the electron transport layer 6 from the hole transport layer 4 was kept at room temperature.

Here, the element on which the electron transport layer 6 was deposited was once taken out of the vacuum deposition apparatus into the atmosphere, and a stripe shadow mask having a width of 2 mm was used as a mask for the cathode deposition, and the ITO of the anode 2 was formed. Adhere to the element so as to be perpendicular to the stripe, and install it in another vacuum evaporation apparatus and set the degree of vacuum in the apparatus to 2 × 10 ^-6 Torr in the same way as for the organic layer
(About 2.7 × 10 ⁻⁴ Pa). As the cathode 7, magnesium fluoride (MgF ₂ ) was first deposited using a molybdenum boat at a deposition rate of 0.05 nm / sec and a degree of vacuum of 3.5 × 10
^{At -6} Torr (about 4.7 × 10 ^-4 Pa), a film was formed on the electron transport layer 6 to a thickness of 1.5 nm. Next, the aluminum was similarly heated by a molybdenum boat to form an aluminum layer having a thickness of 40 nm at a deposition rate of 0.6 nm / sec and a degree of vacuum of 1.0 × 10 ⁻⁵ Torr (about 1.3 × 10 ⁻³ Pa). Further, copper is further heated thereon using a molybdenum boat in order to increase the conductivity of the cathode, and a vapor deposition rate of 0.4 nm / sec and a degree of vacuum of 1.0 × 10 ^−5.
A 40 nm-thick copper layer was formed at Torr (about 1.3 × 10 ⁻³ Pa) to complete the cathode 7. The substrate temperature during the deposition of the three-layer cathode 7 was kept at room temperature.

As described above, an organic electroluminescent device having a light emitting area of 2 mm × 2 mm was manufactured. Table 4 shows the light emission characteristics of this device. In Table 4, the light emission luminance is a value at a current density of 250 mA / cm ² , and the light emission efficiency is 100
The value at cd / m ² , the luminance / current indicate the slope of the luminance-current density characteristic, and the voltage indicates the value at 100 cd / m ² . EL spectrum peak maximum wavelength and CIE chromaticity coordinate value (JIS Z8701)
Are also shown. FIG. 4 shows the luminance-voltage characteristics of this element. After storage for 6 months, no significant increase in the driving voltage was observed, no decrease in luminous efficiency and luminance, and stable storage stability of the device was obtained. Even after storage at a temperature of 60 ° C. and a humidity of 90% for 96 hours, no practical deterioration was observed in the light emitting characteristics of the device.

Comparative Example 1 A device was produced in the same manner as in Example 1 except that the light-emitting layer was not doped with the exemplified compound (III-25). Table 4 shows emission characteristics
FIG. 4 shows the luminance-voltage characteristics. Maximum emission wavelength is 496n
m and blue-green light emission. Comparative Example 2 A device was produced in the same manner as in Example 1 except that the distyrylbiphenyl derivative (B-1) was used as a host material of the light emitting layer. Table 4 shows the light emission characteristics of this device. The luminous efficiency was reduced, and the color purity was also lower than in Example 1. When this device was stored at a temperature of 60 ° C. and a humidity of 90% for 96 hours, a portion having an emission area ratio of 30% emitted green light, which was confirmed to be emission from the aluminum complex used as the electron transport layer. Was found to have low heat resistance.

Comparative Example 3 A device was prepared in the same manner as in Example 1 except that bis (2-methyl-8-quinolinolato) (p-phenylphenolato) aluminum complex (B-2) was used as a host material for the light emitting layer. Produced. Table 4 shows the light emission characteristics of this device. The emission color was green, blue emission was not obtained, and the color purity was lower than that of Example 1. Comparative Example 4 An element was produced in the same manner as in Example 1, except that perylene was used as a doping material for the light emitting layer. Table 4 shows the light emission characteristics of this device, and FIG. 4 shows the luminance-voltage characteristics. No improvement in luminous efficiency was observed, and an increase in drive voltage was observed.

[0064]

[Table 9]

[0065]

According to the organic electroluminescent device of the present invention, it is possible to achieve blue light emission and to obtain a device with improved stability, since it has a light emitting layer containing a specific compound. Accordingly, the organic electroluminescent device according to the present invention can be used as a flat panel display (for example, for an OA computer or a wall-mounted television), a multi-color display device, or a light source (for example, a light source of a copier, a liquid crystal display) utilizing a feature as a surface light emitter. And instrument backlight),
It can be applied to display boards and marker lights, and particularly has a great technical value as an in-vehicle or outdoor display element requiring 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 a graph showing luminance-voltage characteristics of the devices manufactured in Example 1 and Comparative Examples 1 and 4.

[Explanation of symbols]

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

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Tomoyuki Ogata 1000 Kamoshita-cho, Aoba-ku, Yokohama-shi, Kanagawa Prefecture Mitsubishi Chemical Corporation Yokohama Research Laboratory F term (reference) 3K007 AB04 AB14 BA06 CA01 CB01 CC00 DA01 DB03 EB00 FA00 FA01 FA03

Claims (3)

[Claims] 1. An organic electroluminescent device comprising at least a light-emitting layer sandwiched between an anode and a cathode on a substrate,
The light emitting layer has the following general formula (I): (Wherein, R ^{1 to} R ⁶ represent a hydrogen atom, a halogen atom, an alkyl group, an aralkyl group, an alkenyl group, an allyl group, a cyano group, an amino group, an acyl group, an alkoxycarbonyl group,
Having a carboxyl group, an alkoxy group, an alkylsulfonyl group, an α-haloalkyl group, a hydroxyl group, an amide group optionally having a substituent, an aromatic hydrocarbon ring group optionally having a substituent or a substituent. Represents an aromatic heterocyclic group which may be substituted, M represents an Al atom or a Ga atom, and L represents a structure of any of the general formulas (Ia) and (Ib). ) (Wherein, Y represents any atom of Si, Ge, and Sn, and Ar ^{1 to} Ar ⁴ represent an alkyl group, an aralkyl group, an alkenyl group, and an aromatic hydrocarbon ring group which may have a substituent. Or a metal complex represented by an aromatic heterocyclic group) as a host material, and represented by the following general formula (II): (In the formula, Ar ^{5 to} Ar ⁷ each independently represent an aromatic hydrocarbon ring group or an aromatic heterocyclic group which may have a substituent, provided that at least one has 10 to 10 carbon atoms. 30 condensed aromatic ring groups.)
An organic electroluminescent device, characterized in that the organic electroluminescent device contains about 10% by weight. 2. The organic electroluminescent device according to claim 1, wherein a hole transport layer is provided between the light emitting layer and the anode. 3. The organic electroluminescent device according to claim 1, wherein an electron transporting layer is provided between the light emitting layer and the cathode.