JPH06212151A - Organic electroluminescent element - Google Patents

Abstract

PURPOSE:To improve luminance, luminescent efficiency, etc., and inhibit degradation in luminescence by incorporating a specific org. compd. into an electroluminescent element having a phosphor-contg. layer sandwiched between a pair of electrodes. CONSTITUTION:At least one compd. of formula I (wherein R<1> to R<7> are each H, oxygen halogen, cyano, nitro, amino, dialkylamino, diphenylamino, hydroxyl, alkoxy, mercapto, siloxy, acyl, cycloalkyl, carboxyl, sulfo group, etc.; and X is N, S, Se, etc.) (e.g. a compd. of formula II, III, or IV) is incorporated into an electroluminescent element which at least has a phosphor-contg. layer sandwiched between a pair of electrodes. The compd. or its metal complex is effective when incorporated into any of the hole injection layer, the phosphor layer, and the electron injection layer.

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 layer and the amine compound for the hole injecting layer, high-luminance green light emission is obtained.
With a DC voltage of V, a brightness of several hundred cd / m ² and a maximum luminous efficiency of 1.5 lm / W are achieved, which is close to a practical range. However, although the organic EL devices to date have improved the emission intensity due to the improved structure, they 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.

[0003]

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.

[0004]

As a result of intensive investigations by the present inventors, an organic EL device using an organic compound represented by a specific general formula [1] has a large emission intensity and is stable in repeated use. The inventors have found that they are also excellent in properties and have reached the present invention.

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

General formula [1]

[Chemical 2]

[In the formula, R ¹ to R ⁷ are each independently a hydrogen atom, an oxygen 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 or 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 heterocycle Represents a group. Further, it may be an aromatic ring which may have a substituent, an aromatic ring containing a hetero atom or a hetero ring. R ¹ to R ⁷ may have any substituent, may form an aromatic ring or a heterocycle between the substituents, or may form a complex with a metal. X is a nitrogen, sulfur or selenium atom, and the number of R ⁷ bonded to X may be any number. ]

Representative examples of the compound of the general formula [1] used in the present invention are specifically shown in the following formulas (a) to (j), but the present invention is not limited to the following representative examples. Not something. The compound of the general formula [1] used in the present invention may have any substituent.

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]

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 compound represented by the general formula [1] or a metal complex thereof is used as the hole injection layer 3,
It is effective to use it for any of the phosphor layer 4 and the electron injection layer 5.

For the phosphor layer 4 of FIG. 1, if necessary, a hole transporting material or an electron transporting material for carrier transport can be used in addition to the light emitting substance. In the structure of FIG. 2, the phosphor layer 4 and the hole injection layer 3 are separated. This structure allows
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 an electron injection layer 5 in addition to the hole injection layer 3, and improves 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 to improve the transparency of at least the electrode A represented by 2 or the electrode B represented by 6 in order to efficiently emit light. Also,
The substrate 1 is preferably transparent. The transparent electrode is made of the above-mentioned conductive material and has a film thickness set by a method such as vapor deposition or sputtering so as to ensure a predetermined translucency.

The substrate is not limited as long as it has mechanical and thermal strength and is transparent, but for example,
Examples of the transparent resin include a glass substrate, an ITO substrate, a NESA substrate, a polyethylene plate, a polyether sulfone plate, and a polypropylene plate.

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 is used, and the solvent may be any one. . 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] used in the organic EL device of the present invention is effective when used in any of layers 3 to 5. The organic EL device shown in FIG. 1 has the general formula [1]
High light emission characteristics can be achieved by using the above compound. Further, this compound can also obtain a more efficient emission luminance by using an auxiliary agent of a light emitting substance in the same layer.

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

Examples of such known luminescent materials or auxiliaries of known luminescent materials 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 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. Further, 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. In the organic EL devices shown in FIGS. 2 and 3, the compound of the general formula [1] can be used in any of the layers, 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.

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

Example 1 A compound (a) and tris (8-hydroxyquinolinol) aluminum complex were vacuum-deposited at a ratio of 1: 1 on a washed glass plate with an ITO electrode to form a phosphor having a thickness of 0.1 μm. Layers were obtained. On top of that, add magnesium and silver 10:
The alloy mixed in 1 was vapor-deposited to form an electrode having a film thickness of 0.2 μm to obtain the organic EL device shown in FIG. This element is
Light emission of about 200 cd / m ² was obtained at a DC voltage of 5V.

Example 2 Compound (b) and tris (8-hydroxyquinolinol) aluminum complex were dissolved in chloroform at a ratio of 3: 1 and spin-coated to form a phosphor layer.
An organic EL device is manufactured in the same manner as in Example 1 except that it is formed.
A device was produced. This device has a DC voltage of 5V
Light emission of cd / m ² was obtained.

Example 3 Compound (c) was vacuum-deposited on a washed glass plate with an ITO electrode to obtain a hole injection layer having a thickness of 0.04 μm.
Next, 9,10-diphenylanthracene was vacuum-deposited to obtain a phosphor layer having a thickness of 0.04 μm. On top of that, deposit an alloy of magnesium and silver mixed at a ratio of 10: 1,
An electrode having a film thickness of 0.2 μm was formed to obtain the organic EL device shown in FIG. This element is approximately 220 cd / d at a DC voltage of 5V.
A light emission of m ² 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, Tris (8
-Hydroxyquinolinol) aluminum complex was vacuum-deposited to obtain a phosphor layer having a thickness of 0.05 μm. Further, the compound (g) was vacuum-deposited to obtain an electron injection layer having a thickness of 0.03 μm. 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. This device emitted light of about 270 cd / m ² at a DC voltage of 5V.

When all the organic EL devices shown in this example were made to continuously 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.

[0038]

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 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 device used in Example 3.

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

[0000]

[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 ⁷ are each independently a hydrogen atom, an oxygen 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 which may have a substituent, an aromatic ring containing a hetero atom or a hetero ring. R ¹ to R ⁷ may have any substituent, may form an aromatic ring or a heterocycle between the substituents, or may form a complex with a metal. X is a nitrogen, sulfur or selenium atom, and the number of R ⁷ bonded to X may be any number. ]