JP3428051B2 - 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) 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, an EL element is composed of a light emitting layer and a pair of counter electrodes sandwiching the light emitting layer.

Light emission is caused when an electric field is applied between both electrodes.
Electrons are injected from the cathode side, holes are injected from the anode side, the electrons recombine 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. It is a phenomenon.

The conventional organic EL element has a higher driving voltage and lower emission brightness and emission efficiency than the 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 element using an organic compound having a high fluorescence quantum efficiency that emits light at a low voltage of 10 V or less has been reported,
Interesting (see Applied Physics Letters, Vol. 51, p. 913, 1987).

In this method, a metal chelate complex is used for the phosphor thin film layer and an amine compound is used for the hole injection layer to obtain high-luminance green light emission, and the luminance is several hundred cd at a DC voltage of 6 to 7V. / M ² and the maximum luminous efficiency of 1.5 lm / W, which is close to the practical range.

However, the organic EL devices to date have been improved in the emission intensity due to the improved structure, but still do not have sufficient emission brightness. Further, it has a big problem that it is inferior in stability when repeatedly used. Therefore, under the present circumstances, it is desired to develop an organic EL device having a larger emission brightness and excellent stability in repeated use.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide an organic EL device having a large emission intensity and excellent stability in repeated use. As a result of diligent studies by the present inventors, they found that an organic EL element using an organic compound represented by a specific general formula [1] has a large emission intensity and excellent stability during repeated use. The present invention has been reached.

[0008]

That is, the first invention is an electroluminescent device having a layer containing at least a phosphor between a pair of electrodes, and an organic compound represented by the general formula [1] It is an organic electroluminescence device characterized by using at least one kind.

A second aspect of the invention is an electroluminescence 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 a ligand. The organic electroluminescence device according to the first invention is characterized by using a metal complex. General formula

[0010]

[Chemical 2]

(Wherein R ¹ to R ¹⁰ are each independently 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, siloxy group. Group, acyl group, cycloalkyl group, carboxylic acid group, sulfonic acid group, substituted or unsubstituted aliphatic hydrocarbon group, substituted or unsubstituted aromatic hydrocarbon group, substituted or unsubstituted aromatic heterocyclic group R ¹ to R ¹⁰ may have any substituent, but at least one of R ⁶ to R ¹⁰ forms an aromatic ring or a heterocycle between adjacent substituents. , May form a complex with a metal.)

Typical examples of the compound of the general formula [1] used in the present invention are specifically shown in the following compounds (j) to (l), but the present invention is not limited to the following representative examples. Not something.

Compound (j)

[Chemical 12]

Compound (k)

[Chemical 13]

Compound (l)

[Chemical 14]

The compound of the general formula [1] used in the present invention is
A stable metal complex can be formed with a wide range of metal ions. The position of the substituent is not particularly limited, but in order to obtain a stable metal complex, a large number of metals and complexes are formed between> C═O at the 4-position and the hydroxyl group at the 3- or 5-position. Then, the emission intensity can be further improved. Further, the compound of the general formula [1] may have any substituent. The metal constituting the metal complex is beryllium,
Magnesium, aluminum, silicon, scandium,
Titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, gallium, ruthenium, palladium, silver, cadmium, indium, tin, lanthanoid element, actinoid element, etc., but are not limited to these. .

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. The organic compound represented by the general formula [1] or a metal complex thereof is 3
It is effective to use in any of the layers 5 to 5, but since it has a light emitting function, it is desirable to use it in the phosphor layer 4, but it is not limited to this. Phosphor layer 4 of FIG.
If necessary, a hole-transporting material or an electron-transporting material that carries carriers can be used in addition to the light-emitting substance.

The structure shown in FIG. 2 has a phosphor layer 4 and a 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 shown 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. As described above, by forming the organic EL element into a multi-layer structure, it is possible to prevent a decrease in brightness and life due to quenching.

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 at least the electrode A represented by 2 or the electrode B represented by 6 is a transparent electrode in order to emit light efficiently. 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 light-transmitting property 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,
Examples of the transparent resin include a polyethylene plate, a polyether sulfone plate, and a polypropylene plate.

For formation of 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 solution in which the material forming each layer is dissolved or dispersed in an appropriate solvent such as chloroform, tetrahydrofuran, dioxane, etc. is used. Is also good. Further, an appropriate resin or additive may be used for improving film-forming property and preventing pinholes in the film.

The compound of the general formula [1] or its metal complex used in the organic EL device of the present invention is effective when used in any of layers 3 to 5.

In the organic EL device shown in FIG. 1,
High light emission characteristics can be achieved by using the compound of the general formula [1] or a metal complex thereof as a light emitting substance. In addition, this compound can obtain more efficient emission luminance by using an auxiliary agent of a light emitting substance in the same layer.

In the present organic EL device, if necessary, in addition to the compound of the general formula [1] or a metal complex thereof, a known light emitting substance, light emission auxiliary, hole transporting substance, electron transporting substance is used. You can also

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

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 substance, a substance 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.

It is also possible to sensitize by adding an electron accepting substance to the hole transporting substance and adding an electron donating substance to the electron transporting substance. Organic EL shown in FIGS. 2 and 3
In the device, the compound of the general formula [1] or a metal complex thereof can be used in any layer, and at least one of a light emitting substance, a light emission auxiliary, a hole transporting substance and an electron transporting substance is contained in the same layer. May be done. As described above, in the present invention, since the compound of the general formula [1] or the metal complex thereof is used for the organic EL device, the luminous efficiency and the luminous 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. The organic EL device of the present invention can be used as various display devices.

[0042]

The present invention will be described in more detail based on the following examples.

Example 1 A compound of the compound (j) was vacuum-deposited on a washed glass plate with an ITO electrode to obtain a phosphor layer having a thickness of 0.08 μm. An electrode having a film thickness of 0.2 μm was formed thereon with an alloy in which magnesium and silver were mixed at a ratio of 10: 1 to obtain the organic EL device shown in FIG. This device has a DC voltage of 5 V
Light emission of 0 cd / m ² was obtained. Example 2 Example 1 was repeated, except that the phosphor layer was formed by spin coating in which the aluminum complex having the compound of the compound (k) as a ligand and polyvinylcarbazole were dissolved in chloroform at a ratio of 2: 8. An organic EL device was produced by the same method. The device emitted light of about 500 cd / m ² at a DC voltage of 5 V. Examples 3 to 8 Organic compounds were prepared in the same manner as in Example 1 except that a metal complex containing a metal shown in Table 1 was used as a phosphor instead of the aluminum complex containing the compound (k) as a ligand. An EL device was produced. The device emitted the light shown in Table 2 at a DC voltage of 5V. Table 1

[Table 1] Table 2

[Table 2] Example 9 On a washed glass plate with an ITO electrode, N, N'-diphenyl-N, N '-(3-methylphenyl) -1,1'
-Biphenyl-4,4'-diamine was vacuum-deposited to obtain a hole injection layer having a thickness of 0.03 μm. Then, the compound (1) was vacuum-deposited to obtain a phosphor layer having a thickness of 0.02 μm. On top of that, add magnesium and silver 10: 1.
2 is formed by forming an electrode with a film thickness of 0.2 μm using the alloy mixed in
The organic EL device shown in was obtained. This element has a DC voltage of 5V
The emission of about 600 cd / m ² was obtained. Example 10 N, N′-diphenyl-N, N ′-(3-methylphenyl) -1,1′-biphenyl-4,4′-diamine was dissolved in chloroform and spin-coated to a film thickness of 0.03 μm. An organic EL device was manufactured in the same manner as in Example 9 except that a hole injection layer was formed, a compound of the compound (h) was vacuum-deposited on the hole injection layer, and a phosphor layer having a thickness of 0.015 μm was used. It was made. The device emitted light of about 750 cd / m ² at a DC voltage of 5V. Comparative Example 1 A compound of the following compound (a) was vacuum-deposited on a washed glass plate with an ITO electrode to obtain a phosphor layer having a thickness of 0.08 μm. On top of that, add magnesium and silver 10: 1.
Fig. 1
The organic EL device shown in was obtained. This element has a DC voltage of 5V
In this way, a light emission of about 100 cd / m ² was obtained. Compound (a)

[Chemical 15]

Comparative Example 2 In the phosphor layer, an aluminum complex having a compound of the following compound (b) as a ligand and polyvinyl carbazole were used in a ratio of 2:
An organic EL device was produced in the same manner as in Example 1 except that it was dissolved in chloroform at a ratio of 8 and was formed by spin coating. This element has a DC voltage of 5V
Thus, light emission of about 150 cd / m ² was obtained. Compound (b)

[Chemical 16]

Comparative Examples 3 to 8 The same as Example 1 except that a metal complex containing a metal shown in Table 1 was used as the phosphor instead of the aluminum complex containing the compound (b) as a ligand. An organic EL device was produced by the method. The device emitted light shown in Table 3 at a DC voltage of 5V.

Table 3

[Table 3]

Comparative Example 9 N, N'-diphenyl-N, N'-di (3-methylphenyl) -1, on a cleaned glass plate with ITO electrodes
1′-biphenyl-4,4′-diamine was vacuum-deposited to obtain a hole injection layer having a thickness of 0.03 μm. Then, the following compound (e) is vacuum-deposited to a film thickness of 0.02 μm.
m phosphor layer was obtained. On top of that, add 1 magnesium and 1 silver
An electrode having a film thickness of 0.2 μm was formed from the alloy mixed at 0: 1 to obtain the organic EL device shown in FIG. The device emitted light of about 200 cd / m ² at a DC voltage of 5V. Compound (e)

[Chemical 17]

Comparative Example 10 N, N'-diphenyl-N, N'-di (3-methylphenyl) -1,1'-biphenyl-4,4'-diamine was dissolved in chloroform and spin-coated to form a film. A hole injection layer having a thickness of 0.03 μm is formed, and a compound of the following compound (h) is vacuum-deposited on the hole injection layer to form a film having a thickness of 0.015.
An organic EL device was produced in the same manner as in Example 9 except that the phosphor layer of μm was used. This element has a DC voltage of 5
Light emission of about 240 cd / m ² was obtained at V. Compound (h)

[Chemical 18]

When all the organic EL elements shown in this example were continuously made to emit light 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.
Luminescent auxiliary substance, hole transporting substance, electron transporting substance, sensitizer,
The resin, the electrode material and the like and the method for manufacturing the element are not limited.

[0051]

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.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a schematic structure of an organic EL.

FIG. 2 is a cross-sectional view showing a schematic structure of an organic EL.

FIG. 3 is a cross-sectional view showing a schematic structure of an organic EL.

[Explanation of symbols]

1. substrate 2. Electrode A 3. Hole injection layer 4. Phosphor layer 5. Electron injection layer 6. Electrode B

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H05B 33/14 C09K 11/06 CA (STN) REGISTRY (STN)

Claims (2)

(57) [Claims] 1. An electroluminescent device having a layer containing at least a phosphor between a pair of electrodes, wherein at least one organic compound represented by the general formula [1] is used. element. General formula [1] (In the formula, R ¹ to R ¹⁰ are each independently 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. Represents a 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. ¹ to R ¹⁰ may have any substituents, but at least one of R ⁶ to R ¹⁰ forms an aromatic ring or a heterocycle between adjacent substituents. It may form a complex.) 2. The organic electroluminescence device according to claim 1, wherein a metal complex having at least one kind of the compound represented by the general formula [1] as a ligand is used.