JP3151987B2 - Organic electroluminescence device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic electroluminescence (EL) device used for a flat light source and a display.

[0002]

2. Description of the Related Art An EL device using an organic substance is expected to be used as an inexpensive, large-area, full-color display device of a solid light emitting type, and many developments have been made. Generally EL
Is composed of a light-emitting layer and a pair of opposed electrodes sandwiching the layer. In light emission, when an electric field is applied between both electrodes, electrons are injected from the cathode side, and holes are injected from the anode side. Further, the electrons are recombined with holes in the light emitting layer, and energy is emitted as light when the energy level returns from the conduction band to the valence band. The conventional organic EL element has a higher driving voltage and lower light emission luminance and light emission efficiency than the inorganic EL element. In addition, the characteristic deterioration was remarkable, and it had not been put to practical use. In recent years, an organic EL device formed by laminating a thin film containing an organic compound having a high fluorescence quantum efficiency and emitting light at a low voltage of 10 V or less has been reported and has attracted attention (Applied Physics Letters, 51
Vol., P. 913, 1987). in this way,
Using a metal chelate complex for the phosphor layer and an amine compound for the hole injection layer, a high-luminance green light emission is obtained.
At a DC voltage of V, the luminance has reached several hundred cd / m ² and the maximum luminous efficiency has reached 1.5 lm / W. However, organic EL devices up to now have improved light emission intensity due to the improved structure, but do not yet have sufficient light emission luminance. In addition, there is a major problem that the stability upon repeated use is poor. Therefore, at present, it is desired to develop an organic EL device having higher emission luminance and excellent stability when repeatedly used.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide an organic EL device having a high luminous intensity and excellent stability when used repeatedly.

[0004]

As a result of diligent studies by the present inventors, an organic EL device using an organic compound represented by a specific general formula [1] has a large luminous intensity and is stable when repeatedly used. The inventors have also found that the properties are excellent, and have reached the present invention.

That is, the present invention relates to an electroluminescent device having a layer containing at least a phosphor between a pair of electrodes, wherein at least one of the organic compounds represented by the general formula [1] is provided. The organic electroluminescent element is

The general formula [1]

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Wherein R ¹ to R ⁶ each independently represent a hydrogen atom, a halogen atom, a cyano group, a nitro group, an amino group, a dialkylamino group, a diphenylamino group, a hydroxyl group, an alkoxy group, a mercapto group, a siloxy group Represents an acyl group, a cycloalkyl group, a carboxylic acid group, a sulfonic acid group, a substituted or unsubstituted aliphatic hydrocarbon group, a substituted or unsubstituted aromatic hydrocarbon group, or a substituted or unsubstituted aromatic heterocyclic group . Further, it may be an aromatic ring optionally having a substituent, an aromatic ring containing a hetero atom or a hetero ring. R ¹ to R ⁶ may have any substituents, may form an aromatic ring or a heterocyclic ring between the substituents, or may form a complex with a metal. n is a positive integer. ]

Hereinafter, typical examples of the basic skeleton of the compound represented by the general formula [1] used in the present invention will be specifically exemplified by compounds (a) to (e). However, the present invention is not limited to this. The molecular weight of the compound having the basic skeleton may be any, and may be any of a monomer, an oligomer and a polymer, or a mixture thereof.

Compound (a)

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Compound (b)

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Compound (c)

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Compound (d)

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Compound (e)

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The compound of the general formula [1] used in the present invention is
It may have any substituent. FIGS. 1 to 3 show schematic views of an organic EL device used in the present invention. In the figure,
Generally, electrode 2 is an anode and electrode B is 6
Is a cathode. The compound of the general formula [1] or a metal complex thereof is effective when used in any of the hole injection layer 3, the phosphor layer 4, and the electron injection layer 5. If necessary, a hole transporting material or an electron transporting material for transporting carriers can be used for the phosphor layer 4 in FIG. 1 if necessary.
In the structure of FIG. 2, the phosphor layer 4 and the hole injection layer 3 are separated. With this structure, the hole injection efficiency from the hole injection layer 3 to the phosphor layer 4 is improved, and the light emission luminance and the light emission efficiency can be increased. The structure in FIG. 3 has an electron injection layer 5 in addition to the hole injection layer 3 to improve the efficiency of recombination of holes and electrons in the phosphor layer 4. In this manner, by making the organic EL element have a multilayer structure, it is possible to prevent a decrease in luminance and life due to quenching.

As the conductive material used for the anode of the organic EL device, those having a work function of more than 4 eV are preferable, and carbon, aluminum, vanadium, iron, cobalt, nickel, tungsten, silver, gold, etc. Alloys thereof and metal oxides such as tin oxide and indium oxide are used.

As the conductive material used for the anode, 4
Those having a work function smaller than eV are preferable, and magnesium, calcium, titanium, yttrium, lithium, ruthenium, manganese and the like, and alloys thereof are used, but not limited thereto.

In the organic EL device, it is desirable that at least the electrode A indicated by 2 or the electrode B indicated by 6 be transparent in order to emit light efficiently. Further, it is desirable that the substrate 1 is also transparent. The thickness of the transparent electrode is set by using the above-described conductive material by a method such as vapor deposition or sputtering so that a predetermined light-transmitting property is ensured.

The substrate is not limited as long as it has mechanical and thermal strength and is transparent.
Transparent resins such as a glass substrate, an ITO substrate, a NESA substrate, a polyethylene plate, a polyethersulfone plate, and a polypropylene plate can be used.

The layers of the organic EL device according to the present invention can be formed by any of dry film forming methods such as vacuum evaporation and sputtering and wet film forming methods such as spin coating and dipping. Each layer must be set to an appropriate thickness. If the film thickness is too large, a large applied voltage is required to obtain a constant light output, resulting in poor efficiency.
If the film thickness is too small, pinholes and the like are generated, and sufficient light emission luminance cannot be obtained even when an electric field is applied.

In the case of the wet film formation method, a liquid in which the material for forming each layer is dissolved or dispersed in a suitable solvent such as chloroform, tetrahydrofuran, dioxane or the like is used, and any solvent may be used. . Further, an appropriate resin or additive may be used for improving the film forming property, preventing pinholes in the film, and the like. The compound of the general formula [1] used in the organic EL device of the present invention is effective when used in any of layers 3 to 5. By using the compound represented by the general formula [1] in the organic EL device shown in FIG. 1, high emission characteristics can be achieved. In addition, this compound can also achieve higher efficiency of light emission luminance by using a light emitting substance auxiliary agent in the same layer.

The organic EL device of the present invention can
In addition to the compound represented by the general formula [1], a known light-emitting substance, a light-emission aid, a hole-transport substance, and an electron-transport substance can also be used.

Examples of such known luminescent substances or luminescent auxiliary substances include anthracene, naphthalene, phenanthrene, pyrene, tetracene, coronene, chrysene and the like.
Fluorescein, perylene, phthaloperylene, naphthaloperylene, perinone, phthaloperinone, naphthaloperinone, diphenylbutadiene, tetraphenylbutadiene, coumarin, oxadiazole, aldazine, bisbenzoxazoline, bisstyryl, pyrazine, CPD, oxine, aminoquinoline, imine, diphenylethylene, Examples include, but are not limited to, vinylanthracene, diaminocarbazole, pyran, thiopyran, polymethine, merocyanine, imidazole chelated oxinoid compounds, and the like.

As the hole transporting material, oxadiazole, triazole, imidazolone,
Imidazolethione, pyrazoline, tetrahydroimidazole, oxazole, hydrazone, acylhydrazone, stilbene, butadiene, benzidine-type triphenylamine, styrylamine-type triphenylamine, diamine-type triphenylamine, and the like, and derivatives thereof, and polyvinyl carbazole, polysilane, There is a polymer material such as a conductive polymer, but it is not limited thereto.

As the electron transporting substance, an appropriate substance having an electron accepting property is used. For example, anthraquinodimethane,
Examples include, but are not limited to, diphenylquinone, oxadiazole, perylenetetracarboxylic acid, and the like. The sensitization can also be performed by adding an electron-accepting substance to the hole-transporting substance and adding an electron-donating substance to the electron-transporting substance. In the organic EL device shown in FIGS. 2 and 3, the compound of the general formula [1] can be used in any layer, and at least one of a luminescent material, a luminescent auxiliary, a hole transport material, and an electron transport material. May be contained in the same layer.

As described above, in the present invention, since the compound of the general formula [1] was used for the organic EL device, the luminous efficiency and the luminous brightness could be increased. In addition, this element was extremely stable against heat and current, and the degradation, which had been a major problem until now, could be greatly reduced.

The organic EL device of the present invention can be used as various display devices.

The present invention will be described in more detail with reference to the following examples. Example 1 A compound (a) and a tris (8-hydroxyquinolinol) aluminum complex were vacuum-deposited at a ratio of 1: 1 on a washed glass plate with an ITO electrode to obtain a phosphor layer having a thickness of 0.1 μm. Was. Add magnesium and silver 10:
The alloy mixed in Step 1 was deposited to form an electrode having a thickness of 0.2 μm to obtain the organic EL device shown in FIG. This element
Emission of about 180 cd / m ² was obtained at a DC voltage of 5 V.

Example 2 Compound (b) and tris (8-hydroxyquinolinol) aluminum complex were dissolved in chloroform at a ratio of 3: 1, and the phosphor layer was formed by spin coating.
Except for forming, the organic EL was formed in the same manner as in Example 1.
An element was manufactured. This device has about 200
Light emission of cd / m ² was obtained.

Example 3 A compound (c) was dissolved in chloroform on a washed glass plate with an ITO electrode, and a hole injection layer having a thickness of 0.04 μm was formed by spin coating. Next, 9,
10-diphenylanthracene was vacuum-deposited to obtain a phosphor layer having a thickness of 0.04 μm. An alloy in which magnesium and silver were mixed at a ratio of 10: 1 was deposited thereon to form a film having a thickness of 0.1 mm.
An organic EL device shown in FIG. 2 was obtained by forming a 2 μm electrode. This device emitted about 250 cd / m ² at a DC voltage of 5 V.

Example 4 The compound (d) was vacuum-deposited on a washed glass plate with an ITO electrode to obtain a hole injection layer having a thickness of 0.03 μm.
Next, a tris (8-hydroxyquinolinol) aluminum complex was vacuum-deposited to obtain a phosphor layer having a thickness of 0.05 μm. Further, perylene was vacuum-deposited to form a film having a thickness of 0.
An electron injection layer of 03 μm was obtained. An electrode having a thickness of 0.2 μm was formed thereon using an alloy in which magnesium and silver were mixed at a ratio of 10: 1 to obtain an organic EL device shown in FIG. This device emitted light of about 280 cd / m ² at a DC voltage of 5 V.

When all the organic EL devices shown in this embodiment were continuously emitted at 1 mA / cm ² ,
Stable light emission could be observed for 00 hours or more. The organic EL device of the present invention achieves luminous efficiency, improved luminous brightness and longer life, and a luminescent material used in combination therewith,
Luminescence auxiliary substances, hole transport substances, electron transport substances, sensitizers,
It does not limit the resin, the electrode material and the like, and the element manufacturing method.

[0031]

According to the present invention, it is possible to obtain an organic EL device having higher luminous efficiency, higher luminance and longer life than the conventional one.

[0032]

[Brief description of the drawings]

FIG. 1 is a sectional view showing a schematic structure of an organic EL device used in Examples 1 and 2.

FIG. 2 is a sectional view showing a schematic structure of an organic EL device used in Example 3.

FIG. 3 is a sectional view illustrating a schematic structure of an organic EL device used in Example 4.

[Explanation of symbols]

 1. Substrate 2. Electrode A3. 3. Hole injection layer Phosphor layer 5. Electron injection layer 6. Electrode B

Claims (1)

(57) [Claims] 1. An organic electroluminescent device having a layer containing at least a phosphor between a pair of electrodes, comprising at least one compound represented by the general formula [1]. . General formula [1] [Wherein, R ¹ to R ⁶ each independently represent a hydrogen atom, a halogen atom, a cyano group, a nitro group, an amino group, a dialkylamino group, a diphenylamino group, a hydroxyl group, an alkoxy group, a mercapto group, a siloxy group, an acyl group. , A cycloalkyl group, a carboxylic acid group, a sulfonic acid group, a substituted or unsubstituted aliphatic hydrocarbon group, a substituted or unsubstituted aromatic hydrocarbon group, and a substituted or unsubstituted aromatic heterocyclic group. Further, it may be an aromatic ring optionally having a substituent, an aromatic ring containing a hetero atom or a hetero ring. R ¹ to R ⁶ may have any substituents, may form an aromatic ring or a heterocyclic ring between the substituents, or may form a complex with a metal. n is a positive integer. ]