JPH06158040A - Organic electroluminescent element - Google Patents

Abstract

PURPOSE:To obtain the subject element having a high luminous intensity and an excellent stability in repeated use by using a specific org. compd. CONSTITUTION:At least one compd. represented by formula I (wherein X<1> to X<8> are each S provided some of them may be C; R<1> to R<16> are each H, halogen, cyano, nitro, carboxyl, sulfo, a (substd.)arom. hydrocarbon group, a (substd.)arom. heterocyclic group, OR<17>, SR<18>, NR<19>R<29>, SO2NR<21>R<22>, CONHR<23>R<24>, NHCOR<25>, COOR<26>, N=NR<27>, Z(CH2CH2Y)mR<28> [wherein R<17> to R<28> are each H or a (substd.)aliph., arom., or arom. heterocyclic group; Y and Z are each O or S; and (m) is 1-10]; and M is a metal optionally having an atom or atomic group bonded through a single or double bond (e.g. a compd. of formula II) is used in an electroluminescent element which has at least a phosphor-contg. layer sandwiched between a pair of electrodes.

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 is composed of a light emitting layer and a pair of counter electrodes sandwiching the light emitting layer. For light emission, when an electric field is applied between both electrodes, electrons are injected from the cathode side,
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.

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 device using an organic compound having a high fluorescence quantum efficiency which emits light at a low voltage of 10 V or less has been reported and has been attracting attention (Applied Physics Letters, Vol. 51, p. 913, 1987).

In this method, a metal chelate complex is used for the phosphor layer and an amine compound is used for the hole injection layer to obtain high-luminance green light emission, and the luminance is several 1 at a DC voltage of 6 to 7V.
The maximum luminous efficiency is 00 cd / m ² and the maximum luminous efficiency is 1.5 lm / W, which is close to the practical range.

However, although the organic EL devices to date have improved the emission intensity due to the improved structure, they have a serious problem of being inferior in stability during repeated use. 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.

[0008]

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 intensive studies by the present inventors, an organic EL using an organic compound represented by a specific general formula [1]
The inventors have found that the device has high emission intensity and excellent stability upon repeated use, and has completed the present invention.

[0010]

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 to use at least one kind of the organic compound represented by the general formula [1] in an electroluminescence device in which at least a phosphor layer and a hole injection layer are laminated between a pair of electrodes. Is an organic electroluminescent element.

General formula [1]

[Chemical 2]

[In the formula, X ¹ to X ⁸ represent a carbon atom or a sulfur atom, any of which is a sulfur atom. R ¹ to R ¹⁶ are each independently a hydrogen atom, a halogen atom, a cyano group, a nitro group, a carboxylic acid group, a sulfonic acid group, a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted aromatic heterocycle. Base, -NHCOR ²⁵ , -COOR ²⁶ , -N = N-R ²⁷ , R ²⁸ (YCH ₂ CH ₂ ) m Z-, and (wherein R ¹⁷
To R ²⁸ represent a hydrogen atom, a substituted or unsubstituted aliphatic hydrocarbon group, a substituted or unsubstituted aromatic hydrocarbon group, or a substituted or unsubstituted aromatic heterocyclic group, and Y and Z each independently. It represents an oxygen atom or a sulfur atom, and m represents a positive integer of 1 to 20. ) M represents a metal, and M may have an atom or an atomic group bonded through a single bond or a double bond. The substituents R ¹ to R ¹⁶ of the compound used in the present invention will be illustrated in more detail below.

Hydrogen atom, halogen atom such as chlorine atom, bromine atom, iodine atom, cyano group, nitro group, carboxylic acid group, sulfonic acid group, or methyl group, ethyl group,
Substituted or unsubstituted aliphatic hydrocarbon groups such as t-butyl group, n-stearyl group, trichloromethyl group, aminomethyl group, hydroxymethyl group, phenyl group, naphthyl group, anthryl group, 2-methylphenyl group, 4 -Substituted or unsubstituted aromatic hydrocarbon group such as chloromethyl group and 4-dimethylaminonaphthyl group, or substituted or unsubstituted aromatic group such as pyridyl group, carbazolyl group, dibenzofuryl group, benzothiazolyl group and 4-methylpyridyl group Group heterocyclic group, methoxy group, ethoxy group, stearyloxy group, phenoxy group, hexylthio group, t-butylthio group, phenylthio group, amino group, n-butylamino group, diethylamino group, diphenylamino group, dibenzylamino group, etc. However, it is not limited to these substituents. M represents a divalent or higher valent metal atom or a divalent metal atom having a substituent.

The compound of the general formula [1] used in the present invention generally comprises at least one compound of the general formula [2] together with urea and various metals and / or various metal salts, preferably in an organic solvent. It can be produced by heating at. As the organic solvent, methanol, ethanol,
An aliphatic organic solvent having a hydroxyl group such as alcohols such as propyl alcohol, n-butyl alcohol and hexyl alcohol, and glycols such as polyethylene glycol, polypropylene glycol and neopentyl glycol can be widely used. As the metal salt, various conventionally known metal salts can be used.

General formula [2]

[Chemical 3]

[In the formula, B ¹ and B ² represent a carbon atom or a sulfur atom, and A ¹ to A ⁴ have the same meanings as R ¹ to R ^{16 in the} general formula [1]. Specific examples of the general formula [1] used in the present invention include compounds (a) to (f) below.
The present invention is not limited to the following representative examples.

Compound (a)

[Chemical 4]

Compound (b)

[Chemical 5]

Compound (c)

[Chemical 6]

Compound (d)

[Chemical 7]

Compound (e)

[Chemical 8]

Compound (f)

[Chemical 9]

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 organic compound represented by the general formula [1] has an excellent carrier transporting ability, it is effective when used in any of the hole injection layer 3, the phosphor layer 4, and the electron injection layer 5. is there.

The phosphor layer 4 of FIG. 1 may contain a hole transport material or an electron transport material for carrier transport 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. 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 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 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 transparent in order to efficiently emit light. Further, it is desirable that the substrate 1 is also transparent. The transparent electrode A or B is
The above-mentioned conductive material is used, and a method such as vapor deposition or sputtering is set 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 plate, an ITO glass plate, a NESA glass plate, a polyethylene plate, and a polyether. Examples include transparent resins such as sulfone plates and polypropylene plates.

For forming each layer of the organic EL device according to the present invention, any one of a dry film forming method such as vacuum deposition and sputtering and a wet film forming method 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 or the like 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 organic compound represented by 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.

In the organic EL thin film element shown in FIG. 1, by adding the organic compound represented by the general formula [1] in the same layer in addition to the light emitting substance, holes and electrons can be easily emitted from the electrodes. Since it is injected, high light emission characteristics can be achieved. The organic compound represented by the general formula [1] can also be used as a luminescent substance or an auxiliary agent for the luminescent substance.

In the present organic EL device, in addition to the organic compound represented by the general formula [1], known light emitting substances, hole transporting substances and electron transporting substances can be used. Such 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, CP
D, oxine, aminoquinoline, imine, diphenylethylene, vinylanthracene, diaminocarbazole,
Examples include, but are not limited to, pyran, thiopyran, polymethine, merocyanine, imidazole chelated oxinoid compounds and the like.

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 organic compound represented by the general formula [1] 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. May be contained in the same layer. As described above, when the organic compound represented by the general formula [1] is used in the organic EL thin film element, 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 luminance 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.

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

Example 1 Compound (a) and tris (8-hydroxyquinolinol) aluminum metal complex were vacuum-deposited on a washed glass plate with an ITO electrode to obtain a phosphor layer having a film thickness of 500Å. Then, an electrode having a film thickness of 2000 Å 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 5V
Light emission of 00 cd / m ² was obtained.

Example 2 An organic EL device was produced in the same manner as in Example 1 except that the phosphor layer was formed by dissolving the compound (b), diisopropylphenylperylene and polyvinylcarbazole in chloroform and spin coating. did. The device emitted light of about 150 cd / m ² at a DC voltage of 5 V.

Example 3 Compound (c) was vacuum-deposited on a washed glass plate with an ITO electrode to obtain a hole injection layer having a film thickness of 300 Å. Then, (8-hydroxyquinolinol) aluminum metal complex was vacuum-deposited to obtain a phosphor layer having a film thickness of 200 Å.
On top of that, an electrode having a film thickness of 2000 Å was formed from an alloy in which magnesium and silver were mixed at a ratio of 10: 1.
The device was obtained. This device has a DC voltage of 5V and a capacity of about 300 cd.
Light emission of / m ² was obtained.

Example 4 N, N, N ', N'-tetraphenyl-4,4 diaminobiphenyl was dissolved in chloroform and spin-coated to form a hole injection layer having a film thickness of 300 Å, on which a compound ( d) is vacuum-deposited, and a phosphor layer having a film thickness of 150 Å is used.
A device was produced. This device has a DC voltage of 5 V
Light emission of cd / m ² was obtained.

Example 5 Film thickness 50 obtained by vacuum co-evaporating the compound (e) and tris (8-hydroxyquinolinol) aluminum metal complex.
An organic EL device was produced in the same manner as in Example 3 except that the 0Å phosphor layer was used. This element has a DC voltage of 5V
Thus, light emission of about 300 cd / m ² was obtained.

Example 6 1,1-Diphenyl-4,4-bis (4-diethylaminophenyl) butadiene was vacuum-deposited on a washed glass plate with an ITO electrode to obtain a hole injection layer having a film thickness of 300Å. . Then, 9,10-diphenylanthracene was vacuum-deposited to obtain a phosphor layer having a film thickness of 200Å. Then, the compound (f) was vacuum-deposited to obtain an electron injection layer having a film thickness of 200Å. An electrode having a film thickness of 2000 Å was formed on the alloy by mixing magnesium and silver in a ratio of 10: 1 to obtain an organic EL device shown in FIG. This element has a DC voltage of 5 V
Light emission of 50 cd / m ² was obtained. When all the organic EL devices shown in this example were made to continuously emit light at 1 mA / cm ² , stable emission could be observed for 1000 hours or more. INDUSTRIAL APPLICABILITY The organic EL device of the present invention achieves improvement in luminous efficiency, luminous brightness, and long life, and limits the light-emitting substance, hole-transporting material, electron-transporting material, sensitizer, resin, etc. used together. Not something to do.

[0043]

According to the present invention, it is possible to obtain an organic EL device having higher light emission efficiency, higher brightness, and a longer life than those of conventional ones.

[0044]

[Brief description of drawings]

FIG. 1 is a sectional view showing a schematic structure of an organic EL element of the present invention. FIG. 2 is a sectional view showing a schematic structure of the organic EL element of the present invention. FIG. 3 is a sectional view showing a schematic structure of the organic EL element of the present invention.

[0045]

[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, wherein at least one organic compound represented by the general formula [1] is used. element. General formula [1] [In the formula, X ¹ to X ⁸ represent a carbon atom or a sulfur atom, any of which is a sulfur atom. R ¹ to R ¹⁶ are each independently a hydrogen atom, a halogen atom, a cyano group, a nitro group, a carboxylic acid group, a sulfonic acid group, a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted aromatic heterocycle. Base, -NHCOR ²⁵ , -COOR ²⁶ , -N = N-R ²⁷ , R ²⁸ (YCH ₂ CH ₂ ) m Z-, and (wherein R ¹⁷
To R ²⁸ represent a hydrogen atom, a substituted or unsubstituted aliphatic hydrocarbon group, a substituted or unsubstituted aromatic hydrocarbon group, or a substituted or unsubstituted aromatic heterocyclic group, and Y and Z each independently. It represents an oxygen atom or a sulfur atom, and m represents a positive integer of 1 to 20. ) M represents a metal, and M may have an atom or an atomic group bonded through a single bond or a double bond. ] 2. An electroluminescent device comprising at least a phosphor layer and a hole injection layer laminated between a pair of electrodes, wherein at least one organic compound represented by the general formula [1] is used. Organic electroluminescent device.