JPH11135262A - Organic electroluminescent element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain stable luminescent characteristic at high temperature, by providing a positive hole transporting layer with an aromatic diamine containing polyether with high glass transition temperature and a low molecular aromatic amine compound. SOLUTION: A positive hole transporting layer contains an aromatic diamine containing polyether which has a repeating unit represented by formula I or formula II and weight average molecular weight of 1000-10000, and a low molecular aromatic amine compound with molecular weight less than 1000. In the formula I and the formula II, Ar<1> -Ar<9> respectively and independently show bivalent aromatic ring or aromatic complex ring group which can have an substituted group. X and Y are selected from a linking group shown in formula III, formula IV, formula V, formula VI, and formula VII. R' in the formulas III-VII show an alkylene group which can have an substituted group, and R" show an aromatic ring group which can have an alkyl group or a substituted group. There are a method that compounds in the formula I and the formula II are laminated as independent layers, and a method that they are mixed into a single layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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 driving is required (generally 50 to 1000 Hz), 2) High driving voltage (generally about 200 V), 3) It is difficult to achieve full color, and there is a problem with blue in particular, 4) Cost of peripheral driving circuits is high, There is a problem that.

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

[0004] In addition to the electroluminescent device using a low molecular material as described above, poly (p-phenylene vinylene) (Nature, 347, 539, 1990, etc.), poly [ 2-Methoxy-5- (2-ethylhexyloxy) -1,4-phenylenevinylene] (Appl. Phys. Lett., 58, 1982)
P., 1991, etc.), poly (3-alkylthiophene) (Jp.
n. J. Appl. Phys, vol. 30, L1938, 1991, etc.) and the development of electroluminescent devices using polymer materials, and the use of low molecular light emitting materials and electron transfer materials in polymers such as polyvinyl carbazole. Mixed elements (Applied Physics, 61, 1044, 1992)
Is also being developed.

[0005]

In order to apply an organic electroluminescent device to a light source such as a flat panel, a display, and a backlight, 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,
There are drawbacks such that the lifetime is shortened due to local Joule heat generation during element driving, and deterioration such as generation and increase of non-light emitting portions (dark spots) is inevitable.

The main cause of these deteriorations is deterioration of the thin film shape of the organic layer. It is considered that the deterioration of the thin film shape is caused by crystallization (or aggregation) of the organic amorphous thin film due to a temperature rise due to heat generation or the like during element driving. This low heat resistance is considered to be due to the low glass transition temperature (hereinafter abbreviated as Tg) of the material. That is, a low molecular weight (molecular weight of 40
Compounds (in particular, about 0 to 600), especially hole transport materials, often have a low melting point and high symmetry. For example, the aromatic diamine, N, N'-diphenyl-N, N '-(3-methylphenyl) -1,1'-biphenyl-4,4'-diamine (usually called TPD) has a Tg of 60 ° C. The Tg of the starburst type aromatic triamine is 75 ° C. (J. Phys. Chem., 97, 6240,
1993), and the Tg of 4,4′-bis [N- (1-naphthyl) -N-phenylamino] biphenyl having an α-naphthyl group introduced is 96 ° C. (IEICE Technical Report, OME95- Five
4, 1995). An organic amorphous thin film formed from these aromatic amine compounds crystallizes due to an increase in temperature, or causes an interdiffusion phenomenon in a two-layer element structure of a hole transport layer and a light emitting layer. As a result, the light emitting characteristics of the device, particularly, a deterioration phenomenon such as a decrease in luminance and an increase in drive voltage appear, and ultimately leads to a reduction in drive life. Further, even when the element is not driven, the temperature is expected to rise in the steps of vapor deposition, baking (annealing), wiring, sealing, and the like during the element fabrication. Therefore, in order to ensure heat resistance in this case, Tg is also required. Even higher is desirable.

On the other hand, attempts have been made to use a polymer material instead of a low molecular weight compound as a hole transport layer of an organic electroluminescent device. Polyvinyl carbazole (Technical Report of IEICE, OME90-38, 1990) ), Polysilane (Appl. Phys. Lett., 59, 2760, 1991), polyphosphazene (42nd Annual Meeting of the Society of Polymer Science, I-8-07 and I-8-08, 1993) Although polyvinyl carbazole has a high Tg of 200 ° C., it has problems such as traps and the like, and its durability is low. It does not show properties that are high and surpass conventional aromatic diamines. In addition, a hole transport layer in which an aromatic diamine compound is dispersed in 30% to 80% by weight of polycarbonate or PMMA (polymethyl methacrylate) has been studied (Jpn. J. Appl. Phys., Vol. 31, L 960, 1992
), The low-molecular compound acts as a plasticizer to lower Tg, and the device characteristics are also lower than when the aromatic diamine compound is used alone. The aromatic diamine-containing polyether, which is a hole transporting polymer,
Although a Tg exceeding 00 ° C. is disclosed, the light-emitting characteristics and stability of the device are not sufficient (see JP-A-9-188756).

As described above, in actuality, the organic electroluminescent device has a serious problem in heat resistance and driving life of the device for practical use.

The fact that the heat resistance of the organic electroluminescent device is not improved and the light emitting characteristics are unstable is a serious problem for a light source such as a facsimile, a copying machine, and a backlight of a liquid crystal display. This is an undesirable characteristic as an element. This is particularly serious when considering the application to in-vehicle displays.

The present invention has been made in view of the above-mentioned conventional situation, and has as its object to provide an organic electroluminescent device capable of maintaining stable luminescent characteristics at high temperatures.

[0011]

According to the present invention, there is provided an organic electroluminescent device comprising a substrate having a light emitting layer and a hole transport layer sandwiched between an anode and a cathode. The layer has the following general formula (I) or (II)
And a polyether containing aromatic diamine having a weight average molecular weight of 1,000 to 100,000 and a low molecular weight aromatic amine compound having a molecular weight of 1,000 or less.

[0012]

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[0013]

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Where Ar ¹ , Ar ² , Ar ³ , Ar ⁴ , Ar ⁵ ,
Ar ⁶ , Ar ⁷ , Ar ⁸ , and Ar ⁹ each independently represent a divalent aromatic ring residue which may have a substituent, and R ¹ , R ² , R
³ represents an aromatic ring group or an aromatic heterocyclic group which may have a substituent, and X and Y are selected from a direct bond or the following linking group. )

[0015]

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(Wherein R ′ represents an alkylene group which may have a substituent, and R ″ represents an alkyl group or an aromatic ring group which may have a substituent.) The present inventors have conducted intensive studies to provide an organic electroluminescent device capable of maintaining stable light-emitting characteristics at high temperatures. As a result, an aromatic diamine-containing polyether having a high Tg in the hole transport layer and a specific low-molecular aromatic It has been found that by containing a group III amine compound, the heat resistance stability of the organic electroluminescent device is improved, and the present invention has been completed.

In the present invention, the combination of the specific aromatic diamine-containing polyether having a Tg of 100 ° C. or higher and a low molecular weight aromatic amine compound is used to simultaneously improve the luminous characteristics and heat resistance of the device. Made it possible. The improvement of the light emission characteristics according to the present invention is achieved by including a low molecular weight aromatic amine compound having excellent mobility in the hole transport layer, and the heat resistance is improved by an aromatic diamine-containing polyether having a high Tg. Is contained in the hole transport layer.

In the present invention, the hole transport layer can be formed of a layer of an aromatic diamine-containing polyether and a layer of a low molecular weight aromatic amine compound. Further, the hole transport layer can be formed by a mixed layer of an aromatic diamine-containing polyether and a low molecular weight aromatic amine compound.

In the present invention, the low molecular weight aromatic amine compound is represented by the following general formula (III) or the following general formula (I)
Those represented by V) are preferred.

[0020]

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[0021]

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(Wherein, Ar ¹⁰ represents a divalent aromatic reduced residue which may have a substituent or a divalent aromatic heterocyclic residue which may have a substituent; R ⁴ , R ⁵ , R ⁶ , R ⁷
Represents an aromatic substituent which may have a substituent or an aromatic heterocyclic group which may have a substituent, and Z is selected from the following linking groups. )

[0023]

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In the organic electroluminescent device of the present invention, a buffer layer is preferably provided between the anode and the hole transport layer. In this case, the buffer layer preferably contains a porphyrin derivative.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the organic electroluminescent device of the present invention will be described below.

First, the aromatic diamine-containing polyether and the low molecular weight aromatic amine compound according to the present invention will be described.

The aromatic diamine-containing polyether according to the present invention has a repeating unit represented by the above general formula (I) or (II) and has a weight average molecular weight of 1,000 to 100,000.

In the above general formulas (I) and (II),
Ar ^{1 to} Ar ⁹ are preferably a divalent benzene ring, a naphthalene ring, an anthracene ring, or a biphenyl, each of which may independently have a substituent, wherein the substituent is a halogen atom; a methyl group; An alkyl group having 1 to 6 carbon atoms such as an ethyl group; an alkenyl group such as a vinyl group; an alkoxycarbonyl group having 1 to 6 carbon atoms such as a methoxycarbonyl group and an ethoxycarbonyl group; 6, an aryloxy group such as a phenoxy group and a benzyloxy group; and a dialkylamino group such as a diethylamino group and a diisopropylamino group. The substituent preferably includes an alkyl group having 1 to 3 carbon atoms, particularly preferably a methyl group.

R ^{1 to} R ³ are preferably a phenyl group, a naphthyl group, an anthryl group, a pyridyl group, a triazyl group, a pyrazyl group, a quinoxalyl group, a thienyl group, each of which may independently have a substituent. A biphenyl group; a halogen atom; an alkyl group having 1 to 6 carbon atoms such as a methyl group and an ethyl group; an alkenyl group such as a vinyl group; a carbon atom having 1 carbon atom such as a methoxycarbonyl group and an ethoxycarbonyl group. Alkoxycarbonyl groups having 1 to 6 carbon atoms; alkoxy groups having 1 to 6 carbon atoms such as methoxy group and ethoxy group; aryloxy groups such as phenoxy group and benzyloxy group; dialkylamino groups such as diethylamino group and diisopropylamino group. .

X and Y are selected from a direct bond or a linking group shown below.

[0031]

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In the above formula, R 'is preferably a methylene group, a dimethylmethylene group, an ethylene group or a propylene group, and R "is preferably an alkyl group having 1 to 6 carbon atoms such as a methyl group or an ethyl group. Group: an aromatic ring group such as a phenyl group, a naphthyl group, an anthryl group, and a tolyl group.

The aromatic diamine-containing polyethers represented by the general formulas (I) and (II) can be prepared, for example, by the method of Kido et al. (Polymers for Advanced Technologies, Vol. 7, 31).
Page, 1996; JP-A-9-188756).

Preferred specific examples of the aromatic diamine-containing polyether represented by the general formula (I) are shown in Tables 1 to 3, but are not limited thereto.

[0035]

[Table 1]

[0036]

[Table 2]

[0037]

[Table 3]

Preferable specific examples of the aromatic diamine-containing polyether represented by the general formula (II) are shown in Tables 4 and 5, but are not limited thereto.

[0039]

[Table 4]

[0040]

[Table 5]

The low molecular weight aromatic amine compound used in combination with the above-mentioned aromatic diamine-containing polyether includes a tertiary amine substituted with an aromatic ring having a molecular weight of
It is sufficient that the thickness is 1,000 or less, but it is necessary to satisfy the following requirements for the hole transport layer.

That is, the material of the hole transport layer is required to be a material having high hole injection efficiency from the anode and capable of transporting the injected holes efficiently. 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.

As a result of intensive studies, the present inventors have found that the low-molecular aromatic amine compound represented by the general formula (III) or (IV) is extremely effective for the purpose of the present invention. Was.

In the general formulas (III) and (IV), Ar ¹⁰ is preferably an aryl group which may have a substituent.
Benzene ring, naphthalene ring, anthracene ring, binaphthyl, fluorene ring, phenanthrene ring, pyrene ring,
Acridine ring, phenazine ring, phenanthridine ring, phenanthroline ring, bipyridyl ring, biphenyl,
Examples of the substituent include a halogen atom; an alkyl group having 1 to 6 carbon atoms such as a methyl group and an ethyl group; an alkenyl group such as a vinyl group; an alkoxycarbonyl group having 1 to 6 carbon atoms such as a methoxycarbonyl group and an ethoxycarbonyl group; A C1-C6 alkoxy group such as a methoxy group and an ethoxy group; an aryloxy group such as a phenoxy group and a benzyloxy group;
And a dialkylamino group such as a diethylamino group and a diisopropylamino group. As this substituent,
Particularly preferred are a methyl group and a phenyl group.

R ^{4 to} R ⁷ are preferably a phenyl group, a naphthyl group, an anthryl group, a pyridyl group, a triazyl group, a pyrazyl group, a quinoxalyl group, a thienyl group, each of which may independently have a substituent. A biphenyl group, wherein the substituent is a halogen atom; an alkyl group having 1 to 6 carbon atoms such as a methyl group and an ethyl group; an alkenyl group such as a vinyl group; and a 1 to 6 carbon atom such as a methoxycarbonyl group and an ethoxycarbonyl group. An alkoxycarbonyl 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; and a dialkylamino group such as a diethylamino group and a diisopropylamino group.

Z is selected from the following linking groups.

[0047]

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Preferred specific examples of the low molecular weight aromatic amine compound represented by the general formula (III) are shown in Tables 6 and 7, but are not limited thereto.

[0049]

[Table 6]

[0050]

[Table 7]

Preferred specific examples of the low molecular weight aromatic amine compound represented by the general formula (IV) are shown in Table 8.
It is not limited to these.

[0052]

[Table 8]

In the present invention, the method for forming the hole transporting layer from such an aromatic diamine-containing polyether and the low molecular weight aromatic amine compound includes a method in which each is laminated as an independent layer, and a method in which each is mixed and used alone. Although there is a method of forming a layer, any of the methods can achieve the effects of the present invention.

That is, in the present invention, the Tg of the hole transport layer is formed by laminating or mixing such an aromatic diamine-containing polyether and a low molecular weight aromatic amine compound.
Is substantially 100 ° C. or higher, and by improving the heat resistance, it is possible to realize an amorphous thin film that is not easily crystallized. In particular, the interdiffusion of molecules at the interface with the light emitting layer is reduced to 100 ° C. or higher. Sufficiently suppressed even at a high temperature, and the emission characteristics are improved by using a low molecular weight aromatic amine compound having excellent mobility.

Hereinafter, the structure of the organic electroluminescent device of the present invention will be described in detail with reference to the drawings.

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

The substrate 1 serves as a support for the organic electroluminescent device, and may be 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 these synthetic resin substrates, it is necessary to pay attention to gas barrier properties. That is, if the gas barrier property of the substrate is too low, the organic electroluminescent device may be deteriorated by 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 one or both surfaces of the synthetic resin substrate to secure gas barrier properties is also one of the preferable methods.

The anode 2 is provided on the substrate 1, and the anode 2 plays a role of injecting holes into the hole transport layer 4. This anode 2 is usually made of a metal such as aluminum, gold, silver, nickel, palladium, platinum, indium and / or
Alternatively, it is composed of a metal oxide such as a tin oxide, a metal halide such as copper iodide, carbon black, or a conductive polymer such as poly (3-methylthiophene), polypyrrole, or 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 volumes, 2711
P., 1992). The anode 2 may have a laminated structure made of 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 1
000 nm, preferably about 10 to 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.

The hole transport layer 4 is provided on the anode 2. As described above, the material required for the hole transport layer is a material that has a high hole injection efficiency from the anode 2 and that 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 a heat resistance of 100 ° C or more.

In the present invention, as the hole transport material,
Formula (I) or (I) having a Tg of 100 ° C. or higher.
Molecular weight 1,000 to 1 having a repeating unit represented by I)
By using a polyether containing 0.000 aromatic diamine and a low molecular weight aromatic amine compound having excellent mobility and a molecular weight of 1,000 or less in combination, light emission characteristics and heat resistance are improved.

The hole transport layer 4 composed of the aromatic diamine-containing polyether and the low molecular weight aromatic amine compound is formed on the anode 2 by a coating method or a vacuum evaporation method.

The layer made of the aromatic diamine-containing polyether is preferably formed by a coating method.

When the hole transport layer 4 has a laminated structure of an aromatic diamine-containing polyether layer and a low molecular weight aromatic amine compound layer, first, the aromatic compound represented by the general formula (I) or (II) is used. A diamine-containing polyether and, if necessary, an additive such as a binder resin or a coating improver that does not trap holes are added and dissolved to prepare a coating solution, and the anode is formed by a method such as spin coating or dip coating. 2 and dried to form an aromatic diamine-containing polyether layer.

The low molecular aromatic amine compound layer is formed by a coating method or a vacuum evaporation method. In the case of the coating method, except that a coating solution is prepared using a solvent that does not dissolve the aromatic diamine-containing polyether layer already thinned, the coating is performed in the same manner as the aromatic diamine-containing polyether layer, It is laminated. In the case of the vacuum evaporation method, the substrate on which the aromatic diamine-containing polyether layer is formed is placed in a chamber of a vacuum evaporation apparatus, and the inside of the chamber is evacuated to 10 ^-6 Torr by an appropriate vacuum pump. The low-molecular aromatic amine compound previously set in the crucible is evaporated by heating the crucible, and is laminated and formed on a substrate facing the crucible to complete the hole transport layer.

When the stacking order is opposite to the above, a low molecular aromatic amine compound layer is formed by a coating method or a vacuum evaporation method, and then an aromatic diamine-containing polyether layer is formed using a solvent which does not dissolve this layer. What is necessary is just to apply | coat and form and to laminate.

As described above, when the hole transport layer 4 has a laminated structure of the aromatic diamine-containing polyether layer and the low molecular weight aromatic amine compound layer, the film thickness of the aromatic diamine-containing polyether layer is 10 to 100 nm. The thickness of the low molecular aromatic amine compound layer is preferably from 20 to 200 nm, and the total thickness of the hole transport layer is usually from 10 to 300 nm, preferably from 20 to 100 nm.

When the hole transporting layer 4 is formed of a mixed layer of an aromatic diamine-containing polyether and a low molecular weight aromatic diamine compound, the above-described coating solution is prepared by mixing both materials in a desired ratio in advance. The hole transport layer 4 is formed into a thin film in the same manner as in the method of coating.

In this case, the thickness of the hole transport layer 4 is usually
10 to 300 nm, preferably 30 to 100 nm, and the content of the aromatic diamine-containing polyether in the mixture of the aromatic diamine-containing polyether and the low molecular weight aromatic amine compound is:
50-90% by weight, content of low molecular weight aromatic amine compound is 50
It is preferably set to 1010% by weight.

In the present invention, the anode 2 and the hole transport layer 4
It is conceivable to provide an anode buffer layer 3 as shown in FIG. The material used for the anode buffer layer 3 has good contact with the anode 2, can form a uniform thin film, and is thermally stable, that is, has a high melting point and Tg, a melting point of 300 ° C. or higher, and a T
As g, 100 ° C. or higher is required. Further, it is required that the ionization potential is low and that hole injection from the anode 2 is easy and that the hole mobility is high. Conventionally, porphyrin derivatives and phthalocyanine compounds (Japanese Patent Application Laid-Open No. 63-295695) and star-bust type aromatic triamines (Japanese Patent Application Laid-Open No.
No. 8688), a hydrazone compound (JP-A-4-320483), an alkoxy-substituted aromatic diamine derivative (JP-A-4-220995), p- (9-anthryl) -N, N-di-p-
Tolylaniline (JP-A-3-111485), polythienylenevinylene and poly-p-phenylenevinylene (JP-A-4-145192), polyaniline (Appl. Phys. Le)
tt., Vol. 64, p. 1245, 1994), sputtered carbon films (JP-A-8-31573), and metal oxides such as vanadium oxide, ruthenium oxide and molybdenum oxide. (The 43rd Joint Lecture on Applied Physics, 27
a-SY-9, 1996).

Of these, porphyrin compounds or phthalocyanine compounds are often used as the anode buffer layer material. 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 (I
I) 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 The anode buffer layer 3 can also be formed into a thin film in the same manner as the hole transport layer 4. However, in the case of an inorganic substance, a sputtering method, an electron beam evaporation method, Film formation by the CVD method is also possible.

The thickness of the anode buffer layer 3 thus formed is usually 3 to 100 nm, preferably 10 to 50 nm.

The light emitting layer 5 is provided on the hole transport layer 4. The light-emitting layer 5 is formed of a compound capable of efficiently transporting electrons from the cathode 7 toward the hole transport layer 4 between electrodes to which an electric field is applied.

The electron transporting compound used in the light emitting layer 5 needs to be a compound having high electron injection efficiency from the cathode 7 and capable of transporting the injected electrons efficiently. For that purpose, the electron affinity is high, the electron mobility is high, and the stability is excellent.
It is required that the impurities serving as traps are compounds that hardly occur during production or use.

As a material satisfying such conditions, 8
Metal complexes such as aluminum complexes of -hydroxyquinoline (JP-A-59-194393);
[h] quinoline metal complex (JP-A-6-322362),
Bisstyrylbenzene derivatives (JP-A 1-245087 and JP-A 2-222484), rare earth complexes (JP-A 1-225)
No. 6584), distyrylpyrazine derivatives (Japanese Unexamined Patent Publication No.
252793), p-phenylene compounds (JP-A-3-3
No. 3183), thiadiazolopyridine derivatives (Japanese Unexamined Patent Publication No.
-37292), pyrrolopyridine derivatives (Japanese Unexamined Patent Publication No.
37293), naphthyridine derivatives (JP-A-3-2039)
No. 82 gazette) and silole derivatives (The 70th Annual Meeting of the Chemical Society of Japan, 2D102 and 2D103, 1996).

For the purpose of improving the luminous efficiency of the device and changing the luminescent color, for example, doping a fluorescent dye for laser such as coumarin using an aluminum complex of 8-hydroxyquinoline as a host material (J. Appl. Phys. , 65
Vol. 3610, 1989). The advantages of this method are: 1) improved luminous efficiency by high-efficiency fluorescent dye, 2) variable emission wavelength by selecting fluorescent dye, 3) fluorescent dye which causes concentration quenching can be used, 4) fluorescent light with poor thin film property Dyes can also be used, and so on.

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

The light emitting layer 5 can be formed in the same manner as the hole transporting layer 4, but usually a vacuum evaporation method is used. As a method of doping the host material of the light-emitting layer with the above-mentioned fluorescent dye such as a naphthacene derivative, a quinacridone derivative, or perylene, there are a method of co-evaporation and a method of previously mixing an evaporation source at a predetermined concentration. In addition, when each of the above dopants is doped into the light emitting layer, the dopant is generally 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, may be performed only near the cathode interface.

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

As a method for further improving the luminous efficiency of the organic electroluminescent device, an electron transport layer 6 can be further laminated on the light emitting layer 5 as shown in FIG. The compound used for the electron transport layer 6 is required to be capable of easily injecting electrons from the cathode 7 and having a higher electron transport ability. Examples of such an electron transporting material include aluminum complexes of 8-hydroxyquinoline and oxadiazole derivatives (Appl. Phys. Lett., Vol. 55, 148), which have already been mentioned as the light emitting layer material.
9, 1989, etc.) and a system in which they are dispersed in a resin such as PMMA (Appl. Phys. Lett., 61, 2793, 1992),
Phenanthroline derivatives (JP-A-5-331459),
2-t-butyl-9,10-N, N'-dicyanoanthraquinone diimine (Phys. Stat. Sol. (A), 142, 489, 1994),
Examples include n-type hydrogenated amorphous silicon carbide, n-type zinc sulfide, and n-type zinc selenide.

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

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.

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, it is effective to further stack a metal layer having a high work function and being stable to the atmosphere to increase the stability of the device. For this purpose, aluminum, silver, nickel,
Metals such as chromium, gold and platinum are used.

Further, inserting an extremely thin film (0.1 to 5 nm) of LiF, Li ₂ O or the like at the interface between the cathode 7 and the light emitting layer 5 or the electron transporting layer 6 is also an effective method for improving the efficiency of the device. (Appl. Phys. Lett., 70, 152, 1997; IEEE Tran
s. Electron. Devices, 44, 1245, 1997).

FIGS. 1 to 3 show an example of an element structure employed in the present invention, and the present invention is not limited to the illustrated one. For example, the reverse structure of FIG.
That is, the cathode 7, the light-emitting layer 5, the hole transport layer 4, and the anode 2 can be laminated on the substrate in this order, and as described above, at least one of the layers is disposed between two highly transparent substrates. It is also possible to provide the organic electroluminescent device of the invention. Similarly,
2 and 3, it is also possible to laminate the respective constituent layers in a reverse structure.

The present invention can be applied to any of a single organic electroluminescent element, an element having a structure arranged in an array, and a structure in which an anode and a cathode are arranged in an XY matrix. Can be.

[0086]

EXAMPLES Next, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples unless it exceeds the gist thereof.

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

A transparent conductive film of indium tin oxide (ITO) having a thickness of 120 nm was deposited on a glass substrate (manufactured by Geomatic Corporation; electron beam film-formed product; sheet resistance: 15 Ω) by using ordinary photolithography technology and hydrochloric acid etching. Two
An anode was formed by patterning into a stripe having a width of mm.
The patterned ITO substrate was cleaned in the order of ultrasonic cleaning with acetone, water cleaning with pure water, and ultrasonic cleaning with isopropyl alcohol, dried with nitrogen blow, and finally cleaned with ultraviolet and ozone.

The aromatic diamine-containing polyether synthesized by the above-described method (No. (I-5) in Table 1 above; weight average molecular weight 9300; glass transition temperature 190 ° C.) was placed on the glass substrate under the following conditions. Spin-coated: Solvent 1,2-dichloroethane Coating solution concentration 30 [mg / ml] Spinner rotation speed 2500 [rpm] Spinner rotation time 25 [second] Drying condition 90 minutes-natural drying A uniform thin film was formed.

Next, the substrate on which the above-mentioned polyether was coated and formed was set in a vacuum evaporation apparatus. After performing rough exhaust of the above device by an oil rotary pump, the degree of vacuum in the device is 2 × 10 ⁻⁶ T
Evacuation was performed using an oil diffusion pump equipped with a liquid nitrogen trap until the pressure became orr (about 2.7 × 10 ⁻⁴ Pa) or less. Aromatic amine compound represented by the following structural formula in a ceramic crucible placed in the above-mentioned apparatus: 4,4′-bis [N- (1-naphthyl) -N-phenylamino] biphenyl (A-1) Was heated to perform vapor deposition. The degree of vacuum during deposition is 2.8 × 10 ^-6 Torr
(About 3.7 × 10 ⁻⁴ Pa), a film having a thickness of 60 nm was laminated on the polyether film to complete the hole transport layer 4.

[0091]

Embedded image

Subsequently, aluminum 8-hydroxyquinoline complex Al (C ₉ H ₆ NO) ₃ (E-1) represented by the following structural formula was used as a material for the light emitting layer 5 in the same manner as in the case of the hole transport layer. Evaporation was performed. At this time, the crucible temperature of the 8-hydroxyquinoline complex of aluminum was controlled in the range of 275 to 285 ° C., and the degree of vacuum during the deposition was 2.5 × 10 ⁻⁶ Torr (about 3.3 × 10 ⁶ Torr).
^-4 Pa), the deposition rate was 0.3 to 0.4 nm / sec, and the thickness of the deposited light emitting layer was 75 nm.

[0093]

Embedded image

The substrate temperature when the above-described hole transport layer 4 and light emitting layer 5 were vacuum-deposited was kept at room temperature.

Here, the element on which the light-emitting layer 5 was deposited was once taken out of the vacuum deposition apparatus into the atmosphere, and a 2 mm-wide stripe-shaped shadow mask was used as a cathode deposition mask. After being in close contact with the device so as to be perpendicular to the device, it is placed in another vacuum deposition apparatus and the degree of vacuum in the apparatus is set to 2 × 10 ^-6 Torr (about
Evacuation was performed until the pressure became 2.7 × 10 ⁻⁴ Pa) or less. Subsequently, as a cathode 4, an alloy electrode of magnesium and silver was vapor-deposited so as to have a thickness of 44 nm by a binary simultaneous vapor deposition method. Vapor deposition was performed using a molybdenum boat and the degree of vacuum was 1 × 10 ⁻⁵ Torr (about 1.3 × 10
^-3 Pa) and a deposition time of 3 minutes and 20 seconds. The atomic ratio of magnesium to silver was set to 10: 1.5. Subsequently, the cathode 4 was completed by laminating aluminum with a thickness of 40 nm on the magnesium-silver alloy film using a molybdenum boat without breaking the vacuum of the apparatus. The degree of vacuum during aluminum deposition is 1.5 × 10 ^-5 Torr (about 2.0 × 10 ^-3 Pa), and the deposition time is 1 minute
20 seconds. The substrate temperature at the time of vapor deposition of the two-layered cathode of magnesium / silver alloy and aluminum was kept at room temperature.

As described above, an organic electroluminescent device having a light emitting area of 2 mm × 2 mm was obtained.

Table 9 shows the emission characteristics of this device. In Table 9, the emission luminance is a value at a current density of 250 mA / cm ² , the luminous efficiency is a value at 100 cd / m ² , the luminance / current is the slope of the luminance-current density characteristic, and the voltage is 100 cd / m ² . Each value is shown.

From Table 9, it is clear that a device having high luminance and high luminous efficiency was obtained.

Comparative Example 1 An element was manufactured in the same manner as in Example 1 except that only the low-molecular aromatic amine compound (A-1) layer having a thickness of 60 nm was formed as the hole transport layer 4.

Table 9 shows the emission characteristics of this device.

Comparative Example 2 An element was manufactured in the same manner as in Example 1 except that only the aromatic diamine-containing polyether (I-5) layer having a thickness of 30 nm was formed as the hole transport layer 4. Table 9 shows the light emission characteristics of this device.

[0102]

[Table 9]

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

In the same manner as in Example 1,
The following copper phthalocyanine (B-1) placed on a O-glass substrate in a molybdenum boat placed in the device
(The crystal form was β-form) was heated to perform vapor deposition. Vacuum degree 4 × 1
Vapor deposition was performed at 0 ^-6 Torr (about 5.3 × 10 ^-4 Pa) at a vapor deposition rate of 0.1 to 0.2 nm / sec to obtain an anode buffer layer 3 having a thickness of 20 nm.

[0105]

Embedded image

Next, in the same manner as in Example 1, on the anode buffer layer 3, 30 nm of the aromatic diamine-containing polyether (I-5) and the low molecular weight aromatic amine compound (A-
1) After stacking the hole transport layer 4 of 60 nm and the light emitting layer 5 of 75 nm of the 8-hydroxyquinoline complex (E-1), the cathode 7 was formed to complete the device. Table 10 shows the emission characteristics of this device.

From Table 10, it is clear that the introduction of the anode buffer layer achieved a reduction in the driving voltage, resulting in a high-luminance, high-efficiency device.

Comparative Example 3 A device was produced in the same manner as in Example 2 except that only the low molecular weight aromatic amine compound (A-1) having a thickness of 60 nm was used as the hole transport layer 4. The emission characteristics of this device are shown in FIG.

Comparative Example 4 An element was manufactured in the same manner as in Example 2 except that only the aromatic diamine-containing polyether (I-5) layer having a thickness of 30 nm was formed as the hole transport layer 4. Table 10 shows the emission characteristics of this device.

Example 3 As the hole transport layer, the aromatic diamine-containing polyether (I-5) and the low molecular weight aromatic amine compound (A-
1) mixture solution (solvent: chloroform, aromatic diamine-containing polyether: low molecular aromatic amine compound = 5)
6:44 (weight ratio), except that a coating film was formed. Table 10 shows the emission characteristics of this device.

Example 4 As the low molecular weight aromatic amine compound, the following compound (A-
An element was fabricated in the same manner as in Example 3, except that 2) was used. Table 10 shows the emission characteristics of this device.

[0112]

Embedded image

[0113]

[Table 10]

Example 5 The devices fabricated in Examples 2 and 3 were sealed with a photo-curing resin to shut them off from the outside air.
A high-temperature storage test was performed at 0 ° C. FIG. 4 shows a temporal change in luminance when driving at a current density of 15 mA / cm ² , and FIG. 5 shows a temporal change in voltage.

As is clear from FIGS. 4 and 5, the decrease in luminance due to high-temperature storage was greatly alleviated by the use of the polyether layer, and the increase in driving voltage was also suppressed. This improvement in heat resistance can be attributed to suppression of interdiffusion at the interface of the light emitting layer.

Comparative Example 5 The device manufactured in Comparative Example 3 was sealed in the same manner as in Example 5, and then subjected to a high-temperature storage test under the same conditions. Current density
FIG. 4 shows a temporal change in luminance at the time of driving at 15 mA / cm ² , and FIG. 5 shows a temporal change in voltage.

As is clear from FIGS. 4 and 5, the luminance is greatly reduced and the voltage is also greatly increased. This is considered to be a result of the interdiffusion of the hole transport layer and the light emitting layer.

[0118]

As described in detail above, according to the organic electroluminescent device of the present invention, a hole transport layer using a specific aromatic diamine-containing polyether and a low molecular weight aromatic amine compound in combination is formed. An element with improved heat resistance and light emission characteristics can be obtained.

Accordingly, the organic electroluminescent device according to the present invention can be used as a light source (for example, a light source of a copier, a liquid crystal display or an instrument) utilizing the characteristics of a flat panel display (for example, for an OA computer or a wall-mounted television) or a surface light emitter. It can be applied to a backlight light source, a display panel, and a sign lamp, and the technical value thereof is particularly large as an in-vehicle 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 a change over time in luminance during high-temperature storage in Example 5 and Comparative Example 5.

FIG. 5 is a graph showing a change over time of a drive voltage increase during high-temperature storage in Example 5 and Comparative Example 5.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Anode 3 Anode buffer layer 4 Hole transport layer 5 Light emitting layer 6 Electron transport layer 7 Cathode

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[Procedure amendment]

[Submission date] November 19, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0001

[Correction method] Change

[Correction contents]

[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.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tomoyuki Ogata 1000 Kamoshita-cho, Aoba-ku, Yokohama-shi, Kanagawa Prefecture Mitsubishi Chemical Corporation Yokohama Research Laboratory

Claims (6)

[Claims] 1. An organic electroluminescent device in which a hole transporting layer and a light emitting layer sandwiched between an anode and a cathode are formed on a substrate, wherein the hole transporting layer has the following general formula (I) or (II): Having a repeating unit represented by, and an aromatic diamine-containing polyether having a weight average molecular weight of 1,000 to 100,000, and a low molecular weight aromatic amine compound having a molecular weight of 1,000 or less, an organic electric field characterized by comprising Light emitting element. Embedded image Embedded image (Where Ar ¹ , Ar ² , Ar ³ , Ar ⁴ , Ar ⁵ , Ar ⁶ , Ar ⁷ ,
Ar ⁸ and Ar ⁹ each independently represent a divalent aromatic ring residue which may have a substituent; R ¹ , R ² and R ³ each represent an aromatic group which may have a substituent; Represents an aromatic group or an aromatic heterocyclic group, and X and Y are selected from a direct bond or the following linking groups. ) (In the formula, R ′ represents an alkylene group which may have a substituent, and R ″ represents an alkyl group or an aromatic ring group which may have a substituent.) 2. The organic electroluminescent device according to claim 1, wherein the hole transport layer is formed of a layer containing an aromatic diamine-containing polyether and a layer containing a low molecular weight aromatic amine compound. . 3. The organic electroluminescent device according to claim 1, wherein the hole transport layer is formed of a layer containing a mixture of an aromatic diamine-containing polyether and an aromatic amine compound. 4. The organic compound according to claim 1, wherein the low molecular weight aromatic amine compound is represented by the following general formula (III) or the following general formula (IV). Electroluminescent device. Embedded image Embedded image (Wherein, Ar ¹⁰ represents a divalent aromatic ring residue which may have a substituent or a divalent aromatic heterocyclic residue which may have a substituent, and R ⁴ , R ⁵ , R ⁶ and R ⁷ represent an aromatic ring group which may have a substituent or an aromatic heterocyclic group which may have a substituent, and Z is selected from the following linking groups. ) 5. The organic electroluminescent device according to claim 1, wherein a buffer layer is provided between the anode and the hole transport layer. 6. The organic electroluminescent device according to claim 5, wherein the buffer layer contains a porphyrin derivative.