JPH06212152A - Organic electroluminescent element - Google Patents

Abstract

PURPOSE:To provide a high-reliability EL element which has high luminance and emission efficiency and hardly undergoes degradation in luminescence. CONSTITUTION:An azo compd. having at least one azo group having a group capable of forming a complex with a metal, or a complex of the azo compd. with a metal, is incorporated into an org. EL element at least having a phosphor sandwiched between a pair of electrodes. Thus is obtd. the objective element having a high luminous intensity and an excellent stability during repeated use.

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) element used for a flat light source or a display.

[0002]

2. Description of the Related Art An EL element using an organic substance is expected to be used as a solid-state light emitting type inexpensive large area full color display element, and many developments have been made. Generally EL
Is composed of a light emitting layer and a pair of counter electrodes sandwiching the light emitting 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, this is a phenomenon in which 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. A conventional organic EL element has a higher driving voltage and lower emission brightness and emission efficiency than an inorganic EL element. In addition, the deterioration of the characteristics was remarkable and it was not put to practical use. In recent years, an organic EL device in which a thin film containing an organic compound having a high fluorescence quantum efficiency that emits light at a low voltage of 10 V or less is stacked has been reported and attracted attention (Applied Physics Letters, 51.
Vol., Page 913, 1987). in this way,
Using the metal chelate complex for the phosphor thin film layer and the amine compound for the hole injecting layer, high-luminance green emission is obtained.
With a DC voltage of up to 7 V, a brightness of several 100 cd / m ² and a maximum luminous efficiency of 1.5 lm / W are achieved, which is close to the practical range. However, the emission intensity of the organic EL elements up to the present has been improved by the improvement of the structure,
It has a major problem of poor stability when used repeatedly. Therefore, under the present circumstances, there is a demand for the development of an organic EL element having a larger light emission intensity and excellent stability in repeated use.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a thin film EL device having a large emission intensity and excellent stability in repeated use. As a result of intensive studies by the present inventors, an organic E having at least a phosphor between a pair of electrodes
The L element contains an azo compound consisting of at least one azo group having a substituent forming a complex with a metal,
Furthermore, they have found that an organic EL element using a metal complex of an azo compound and at least one metal has a large emission intensity and excellent stability during repeated use, and has reached the present invention.

[0004]

That is, the first invention is an electroluminescence device having a layer having at least a phosphor between a pair of electrodes and having a substituent group which forms a complex with a metal. , An organic electroluminescence device containing an azo compound having at least one azo group. A second invention is an electroluminescence device having a layer containing at least a phosphor between a pair of electrodes, and an organic compound containing a metal complex of an azo compound having at least one azo group and at least one metal. It is an electroluminescence element.

The substituents of the azo compound are, independently of each other,
Hydrogen atom, halogen atom, cyano group, nitro group, amino group, dialkylamino group, diphenylamino group, hydroxyl group, alkoxy group, mercapto group, siloxy group, acyl group, cycloalkyl group, carboxylic acid group, sulfonic acid group, substitution Alternatively, it is an unsubstituted aliphatic hydrocarbon group, a substituted or unsubstituted aromatic hydrocarbon group, or a substituted or unsubstituted aromatic heterocyclic group, but is not limited thereto. Further, a ring such as an aromatic ring or a heterocycle may be formed between the substituents.

The substituents contained in the azo compound used in the present invention are illustrated in more detail below. Hydrogen atom, or halogen atom such as chlorine atom, bromine atom, iodine atom, cyano group, nitro group amino group, hydroxyl group, mercapto group, siloxy group, acyl group, cycloalkyl group,
Carboxylic acid group, sulfonic acid group, or substituted or unsubstituted aliphatic hydrocarbon group such as methyl group, ethyl group, t-butyl group, n-stearyl group, trichloromethyl group, aminomethyl group and hydroxymethyl group, phenyl Group, naphthyl group, anthryl group, 2-methylphenyl group, 4-chloromethyl group, substituted or unsubstituted aromatic hydrocarbon group such as 4-dimethylaminonaphthyl group, or pyridyl group,
Substituted or unsubstituted aromatic heterocyclic group such as carbazolyl group, dibenzofuryl group, benzothiazolyl group, 4-methylpyridyl group, methoxy group, ethoxy group, stearyloxy group, phenoxy group, hexylthio group, t-butylthio group, phenylthio group Group, amino group, n-butylamino group, dimethylamino group, diphenylamino group, methylphenylamino group, dibenzylamino group, carbazole group and the like, but are not limited to these substituents.

The representative examples of the azo compounds used in the present invention will be illustrated more specifically below, but the present invention is not limited to the following representative examples. Also, any number of azo groups may be used. The metal of the metal complex of these compounds may be any metal.

1 to 3 show the organic EL used in the present invention.
A schematic diagram of the device is shown. In the figure, the electrode A is generally 2
Is an anode, and electrode 6 is a cathode.

Compound (a)

[Chemical 1]

Compound (b)

[Chemical 2]

Compound (c)

[Chemical 3]

Compound (d)

[Chemical 4]

Compound (e)

[Chemical 5]

Compound (f)

[Chemical 6]

Compound (g)

[Chemical 7]

Compound (h)

[Chemical 8]

Compound (i)

[Chemical 9]

The compound of the present invention and its metal complex are effective when used in any of the hole injection layer 3, the phosphor layer 4 and the electron injection layer 5, but the metal complex has excellent light emitting characteristics. Since it is included, it is desirable to use it for the phosphor layer 4, but it is not limited to this. In addition to the light emitting substance, a light emission assisting substance, a hole transporting material for transporting carriers, and an electron transporting material can be used for the phosphor layer 4 of FIG. 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 emission brightness and the emission efficiency can be increased. The structure of FIG. 3 has a hole injection layer 3
In addition, the electron injection layer 5 is provided to improve the efficiency of recombination of holes and electrons in the phosphor layer 4.

As the conductive material used for the anode of the organic EL device, those having a work function larger than 4 eV are suitable, and carbon, aluminum, vanadium, iron, cobalt, nickel, tungsten, silver, gold and the like, and Those alloys and metal oxides such as tin oxide and indium oxide are used.

The conductive material used for the anode is 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 the electrode A represented by at least 2 or the electrode B represented by 6 is a transparent electrode in order to efficiently emit light. Further, it is desirable that the substrate 1 is also transparent. Transparent electrode A or B
Is set using the above-mentioned conductive material so as to ensure a predetermined translucency by a method such as vapor deposition or sputtering.

The substrate 1 is not limited as long as it has mechanical and thermal strength and is transparent. For example, a glass substrate, an ITO glass plate, a NESA glass plate, a polyethylene plate or a poly Examples include transparent resins such as ether sulfone plates and polypropylene plates.

For forming each layer of the organic EL device according to the present invention, any of dry film forming methods such as vacuum deposition and sputtering and wet film forming methods such as spin coating and dipping can be applied. It is necessary to set each layer to an appropriate film thickness. If the film thickness is too thick, a large applied voltage is required to obtain a constant light output, resulting in poor efficiency.
If the film thickness is too thin, pinholes and the like will occur, and even if an electric field is applied, sufficient emission brightness cannot be obtained.

In the case of the wet film forming method, a liquid in which the material forming each layer is dissolved or dispersed in an appropriate solvent such as chloroform, tetrahydrofuran, dioxane, etc. is used, but any solvent may be used. Further, an appropriate resin or additive may be used for improving film-forming property and preventing pinholes in the film.

The azo compound and its metal complex used in the organic EL device of the present invention are effective when used in any of layers 3 to 5. If necessary, in addition to the azo compound and the metal complex thereof, known luminescent substances, hole transporting substances, and electron transporting substances can be used in the present organic EL device. Such known luminescent substances include anthracene, naphthalene, phenanthrene, pyrene, tetracene, coronene, chrysene, fluorescein, perylene,
Phthaloperylene, naphthaloperylene, perinone, phthaloperinone, naphthaloperinone, diphenylbutadiene,
Tetraphenyl butadiene, coumarin, oxadiazole, ardazine, bisbenzoxazoline, bisstyryl, pyrazine, CPD, oxine, aminoquinoline, imine, diphenylethylene, vinylanthracene, diaminocarbazole, pyran, thiopyran, polymethine,
Examples thereof include, but are not limited to, merocyanine, imidazole chelated oxinoid compound and the like, and their derivatives.

As the hole transport material, oxadiazole, triazole, imidazolone, which are electron donating materials,
Imidazolethione, pyrazoline, tetrahydroimidazole, oxazole, hydrazone, acylhydrazone, stilbene, butadiene, benzidine type triphenylamine, styrylamine type triphenylamine, diamine type triphenylamine, and their derivatives, and polyvinylcarbazole, polysilane, There is a polymer material such as a conductive polymer, but the material is not limited to these.

As the electron transporting material, a material having an appropriate electron accepting property is used. For example, anthraquinodimethane,
Examples thereof include, but are not limited to, diphenylquinone, oxadiazole, and perylene tetracarboxylic acid. Further, an electron accepting substance may be added to the hole transporting substance, and an electron donating substance may be added to the electron transporting substance to sensitize.

In the organic EL devices shown in FIGS. 2 and 3, the azo compound and its metal complex can be used in any of the layers, and at least one of a light emitting substance, a hole transporting substance and an electron transporting substance can be used. It may be contained in one layer. As described above, when the azo compound and / or its metal complex is used in the organic EL device, it is possible to increase the charge injection efficiency, and as a result, it is considered that the light emission efficiency and the light emission brightness can be increased. Further, this element is very stable against heat and current, and the deterioration, which has been a big problem until now, could be greatly reduced. Organic E of the present invention
The L element can be used as various display elements.

[0029]

The present invention will be described in more detail based on the following examples. Example 1 An aluminum complex of compound (b) was vacuum-deposited on a washed glass plate with an ITO electrode to obtain a phosphor layer having a thickness of 0.06 μm. On top of that, add magnesium and silver 10:
An electrode with a thickness of 0.2 μm was formed from the alloy mixed in 1.
The organic EL device shown in FIG. 1 was obtained. With this device, light emission of about 250 cd / m ² was obtained at a DC voltage of 5V.

Example 2 Example 2 was repeated except that the phosphor layer was formed by spin coating in which the indium complex of compound (a), diisopropylphenylperylene and polyvinylcarbazole were dissolved in chloroform at a ratio of 2: 1: 7. An organic EL device was produced in the same manner as in 1. The device emitted light of about 200 cd / m ² at a DC voltage of 5V.

Example 3 A compound (g) 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.
Then, (8-hydroxyquinolinol) aluminum metal complex was vacuum-deposited to obtain a phosphor layer having a thickness of 0.02 μm. Then, an electrode having a film thickness of 0.2 μm was formed from 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 has a DC voltage of 5 V
Light emission of 40 cd / m ² was obtained.

Example 4 Compound (i) was dissolved in chloroform and spin-coated to form a hole injection layer having a thickness of 0.03 μm.
An organic EL device was produced in the same manner as in Example 3 except that the lutetium complex of the compound (d) was vacuum-deposited thereon and a phosphor layer having a thickness of 0.02 μm was used. This device emitted light of about 270 cd / m ² at a DC voltage of 5V.

Example 5 Example 3 was repeated, except that the compound (f) and tris (8-hydroxyquinolinol) aluminum metal complex were co-evaporated in a vacuum at a ratio of 1: 1 and a phosphor layer having a thickness of 0.05 μm was used. An organic EL device was produced by the same method. With this device, light emission of about 250 cd / m ² was obtained at a DC voltage of 5V.

Example 6 1,1-Diphenyl-4,4-bis (4-diethylaminophenyl) butadiene was vacuum-deposited on a washed glass plate with an ITO electrode to form a hole injection layer having a thickness of 0.03 μm. Obtained. Then, 9,10-diphenylanthracene was vacuum-deposited to obtain a phosphor layer having a thickness of 0.02 μm. Then, the compound (g) is vacuum-deposited to a film thickness of 0.01 μm.
The electron injection layer of was obtained. On top of that, add 1 magnesium and 1 silver
An electrode having a thickness of 0.2 μm was formed from the alloy mixed with 0: 1 to obtain the organic EL device shown in FIG. With this device, light emission of about 260 cd / m ² was obtained at a DC voltage of 5V.

When all the organic EL devices shown in this embodiment were made to emit light continuously at 1 mA / cm ² , 10
Stable light emission could be observed for 00 hours or more. The organic EL device of the present invention achieves improvement in luminous efficiency, luminous brightness, and long life.
The hole transport material, electron transport material, sensitizer, resin and the like are not limited.

[0036]

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

[0037]

[Brief description of drawings]

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

FIG. 2 is a sectional view showing a schematic structure of an organic EL element used in Examples 3 to 5.

FIG. 3 is a sectional view showing a schematic structure of an organic EL device used in Example 6.

[Explanation of symbols]

 1: Substrate 2: Electrode A 3: Hole injection layer 4: Phosphor layer 5: Electron injection layer 6: Electrode B

Claims (2)

[Claims] 1. An electroluminescent device having a layer containing at least a phosphor between a pair of electrodes, containing an azo compound having a substituent forming a complex with a metal and having at least one azo group. An organic electroluminescence device characterized by being. 2. An electroluminescent device having a layer containing at least a phosphor between a pair of electrodes, containing a metal complex of an azo compound having at least one azo group and at least one metal. The organic electroluminescence device according to claim 1, which is characterized in that.