JPH06228551A - Organic electroluminescent element - Google Patents

Abstract

(57) [Summary] (Correction) [Purpose] To provide an electroluminescence device having high brightness and high light emission efficiency, low emission deterioration, and high reliability. An electroluminescent element having at least a phosphor between a pair of electrodes, wherein at least one organic compound represented by the following general formula is used. (In the formula, R ¹ to R ¹⁸ are H, halogen atom, CN
Group, nitro group, amino group, dialkylamino group, diphenylamino group, OH, alkoxy group, SH group, siloxy group, acyl group, cycloalkyl group, carboxylic acid group, sulfonic acid group, aliphatic hydrocarbon group, aromatic A hydrocarbon group, a plurality of cyclic groups, etc., and A and B represent different oxygen atoms, sulfur atoms, and —NR ¹⁹ . R ¹⁹ may be any substituent. )

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 in which thin films containing an organic compound having a high fluorescence quantum efficiency that emits light at a low voltage of 10 V or less are laminated
The device has been reported and is of great interest (see Applied Physics Letters, 51, 913, 1987). In this method, the metal chelate complex is added to the phosphor layer,
High-luminance green light emission is obtained by using an amine compound in the hole injection layer, and the luminance is several hundreds at a DC voltage of 6 to 7V.
It has cd / m ² and a 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.

[0005]

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 device using an organic compound represented by the general formula [1] has high emission intensity and excellent stability during repeated use. Came to.

[0006]

That is, the present invention relates to an electroluminescent device having a layer containing at least a phosphor between a pair of electrodes, and has the general formula [1]
It is an organic electroluminescent element using at least 1 type of the organic compound shown by.

General formula [1]

[0008]

[Chemical 2]

(In the formula, R ¹ to R ¹⁸ 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, 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, A substituted or unsubstituted heterocyclic group, which may form an aromatic ring or a heterocyclic ring between the two substituents, and A and B represent different oxygen atoms, sulfur atoms, and -NR ^{19. 19} may be any substituent.)

The representative examples of the compound of the general formula [1] used in the present invention are specifically exemplified by the compounds (a) to (o), but the present invention is limited to the following representative examples. Not a thing.

Compound (a)

[Chemical 3]

Compound (b)

[Chemical 4]

Compound (c)

[Chemical 5]

Compound (d)

[Chemical 6]

Compound (e)

[Chemical 7]

Compound (f)

[Chemical 8]

Compound (g)

[Chemical 9]

Compound (h)

[Chemical 10]

Compound (i)

[Chemical 11]

Compound (j)

[Chemical 12]

Compound (k)

[Chemical 13]

Compound (l)

[Chemical 14]

Compound (m)

[Chemical 15]

Compound (n)

[Chemical 16]

Compound (o)

[Chemical 17]

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. Since the compound of the general formula [1] has both strong light emission and a large carrier transport ability, the hole injection layer 3, the phosphor layer 4,
It is effective to use any of the electron injection layers 5. For the phosphor layer 4 of FIG. 1, if necessary, a light emission auxiliary agent, a hole transport material for carrying carriers, and an electron transport material 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 cathode 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 transparent in order to efficiently emit light. Further, it is desirable that the substrate 1 is also transparent. The transparent electrode is made of the above-mentioned conductive material and is set by a method such as vapor deposition or sputtering so as to ensure a predetermined translucency.

The substrate 1 is not limited as long as it has mechanical and thermal strength and is transparent, but examples thereof include a glass substrate, an ITO substrate, a NESA substrate, a polyethylene plate, and a polyether sulfone. Examples include transparent resins such as plates and polypropylene plates.

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. The film thickness is not particularly limited, but each layer needs to be set 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 or dioxane is used, and 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.

In the organic EL device shown in FIG. 1,
By using the compound of the general formula [1] as the light emitting substance, high light emitting characteristics can be achieved. 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], known light emitting substances, light emission auxiliary agents, hole transporting substances and electron transporting substances can be used.

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-transporting substance, oxadiazole, triazole, imidazolone, which are electron-donating substances,
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 transport 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] 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 may be contained in the same layer. . As described above, in the present invention, since the compound of the general formula [1] 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.

[0041]

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

Example 1 Compound (e) was dissolved in chloroform on a washed glass plate with an ITO electrode, and a phosphor layer was formed by spin coating to obtain a phosphor layer having a thickness of 0.05 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 element has a DC voltage of 5V
A luminescence of 0 m ² was obtained.

Example 2 Organic E was prepared in the same manner as in Example 1 except that the phosphor layer was formed by vacuum deposition using the compound (g).
An L element was produced. This device has a DC voltage of 5 V
A luminescence of 0 m ² was obtained.

Example 3 N, N'-diphenyl-N, N '-(3-methylphenyl) -1,1' was placed on a washed glass plate with an ITO electrode.
-Biphenyl-4,4'-diamine was vacuum-deposited to obtain a hole injection layer having a thickness of 0.03 μm. Next, the compound (i) was dissolved in chloroform and spin coating was performed 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 element is approximately 290 cd / m ² at a DC voltage of 5 V.
Luminescence was obtained.

Example 4 N, N'-diphenyl-N, N '-(3-methylphenyl) -1,1' was placed on a washed glass plate with ITO electrodes.
-Biphenyl-4,4'-diamine was vacuum-deposited to obtain a hole injection layer having a thickness of 0.03 μm. Next, the compound (k) was dissolved in chloroform and spin coating was performed to obtain a phosphor layer having a thickness of 0.02 μm. further,
Perylene was vacuum-deposited to obtain an electron injection layer having a thickness of 0.03 μm. An electrode having a film thickness of 0.2 μm was formed on it by an alloy in which magnesium and silver were mixed at a ratio of 10: 1 to obtain an organic EL device shown in FIG. The device emitted light of about 320 cd / m ² at a DC voltage of 5V.

When all the organic EL devices shown in this example 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.
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.

[0047]

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.

[0048]

[Brief description of drawings]

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

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

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

[Explanation of symbols]

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

Claims (1)

[Claims] 1. An electroluminescent device having a layer containing at least a phosphor between a pair of electrodes, wherein at least one compound represented by the general formula [1] is used. . General formula [1] (In the formula, R ¹ to R ¹⁸ 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. 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, substituted or unsubstituted It is a substituted heterocyclic group and may form an aromatic ring or a heterocyclic ring between two substituents.
And B are different oxygen atoms, sulfur atoms, -NR
Represents ¹⁹ . R ¹⁹ may be any substituent. )