JP3102867B2 - Light emitting element - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an electroluminescent device (electroluminescence (EL) device) for performing charge injection.

(Background technology)

EL devices are generally classified into intrinsic EL devices and injection EL devices. Among these, the operation mechanism of the injection type EL element is to apply a forward bias to a pn junction such as a diode, inject electrons and holes from the electrodes on both sides, and generate light by recombination. It is. Generally, this EL element
A light-emitting element having a structure in which a layer (light-emitting layer) exhibiting the light-emitting function described above is arranged between two electrodes, and a voltage is applied between the electrodes to directly convert electric energy into light. . As a feature of this element, it operates in a wide driving frequency range from DC to AC, and can be driven at a low voltage, and has a good conversion efficiency from electricity to light. Unlike incandescent lamps, fluorescent lamps, etc., various shapes such as thin-film panels, belts, cylinders, etc., for example, display members for lines, figures, images, etc., or planar light emission from large-area panels, etc. It has the potential to realize the body.

Conventionally, inorganic materials such as GaP have been mainly used as the material used for the injection type EL element. On the other hand, recently, a thin film of an organic compound having both hole conductivity and electron conductivity has been developed.
Layered injection light emitting diode devices were reported (CW
Tang: Appl. Phys. Lett., 51 (12) , (1987) 193). A light-emitting element using the organic material has attracted attention because of its features such as various thin film formation methods and the ability to accurately form a large area thin film.

However, when an element is formed using only an organic material for EL that is currently known, the intensity of light emission is limited to some extent.
In addition, there is a problem such as unstable light emission intensity and it has not yet been put to practical use, and it is possible to manufacture a large area and uniform thin film, and it is rich in mass productivity and advantageous in cost. Is strongly required. In this regard, the present inventor has proposed a light emitting device in which a charge injection layer made of an inorganic semiconductor thin film and a light emitting layer made of an organic compound are laminated between electrodes in Japanese Patent Application No. 63-292467.

The present inventors have further studied and found a light-emitting element having excellent durability and will disclose it here.

[Disclosure of the Invention]

That is, the present invention includes two electrode layers,
A light-emitting element provided with a light-emitting layer having an organic compound thin film layer composed of an extended conjugated quinone-based compound between two electrode layers, and preferably an organic compound thin-film layer composed of a mixed layer of a metal complex and an extended conjugated quinone-based compound. A light-emitting element having a light-emitting layer having a light-emitting layer, and more preferably a light-emitting element having a structure in which the light-emitting layer and the charge injection layer are stacked, and the light-emitting layer and the injection layer are interposed between two electrode layers. is there.

 Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 shows one embodiment. 2
This is a light emitting device having two electrode layers 2 and 4 and a light emitting layer having an organic compound thin film layer 3 interposed between the two electrodes 2 and 4. This organic compound thin film layer may be composed of an extended conjugated quinone-based compound, or may be composed of a mixed layer (or laminated) of a metal complex and an extended conjugated quinone-based compound. FIG. 2 shows another embodiment of the present invention, in which an organic compound thin film layer 13 and a charge injection layer 15 are laminated between electrodes 12 and 14. The second
In the figure, the electrode in contact with the charge injection layer is called a first electrode, and the electrode in contact with the organic compound thin film layer is called a second electrode.

The organic compound thin film layer in the present invention is composed of an extended conjugated quinone-based compound, and as a more preferred embodiment, is an organic compound thin film composed of a metal complex and an extended conjugated quinone-based compound. Used by lamination. Preferably, it is a thin film in a state where an extended conjugated quinone compound is mixed in a metal complex.

As the extended conjugated quinone-based compound, parabenzoquinone, diphenoquinone, stilbenequinone, the compounds represented by general structural formulas 1 and 2, and derivatives thereof are effective. Is an organic compound having a π-electron system and easily excited. In the structural formula 1, X represents an atom such as oxygen (O), sulfur (S), and selenium (Se). Derivatives such as redenebisbenzoquinone. Structural formula 2 is dihydrothienothiophenediilidenebisbenzoquinone and its derivatives. In these structural formulas, R is hydrogen, methyl, ethyl, propyl, tertiary butyl, methoxy, ethoxy, halogen, phenyl, phenoxy, hydroxy (OH)
Group, a mercapto (SH) group, an amino group and the like. n is 1,2,3 and 4.

The metal complex in the present invention is a complex compound formed from a metal and an organic ligand. Specifically,
Al, Ga, Ir, Zn, Cd, Mg, Pb, T
a, Tb, Eu, etc., and are not particularly limited. As ligands for organic substances, porphyrin, chlorophyll, 8-hydroxyquinoline (oxine (Ox)), 5,
7-dibromooxin, 5,7-diiodoxin, thiooxin, selenooxin, methyloxin, phthalocyanine, salicylaldehyde oxime, 1-nitroso-2
Naphthol, kuferon, dithizone, acetylacetone and the like are used.

Further, in the present invention, having a high emission quantum efficiency,
It does not prevent the use of an organic compound which has a π-electron system which is easily subjected to external perturbation and which is easily excited, in combination with a metal complex. Examples of the organic compound include condensed polycyclic aromatic hydrocarbons, p-terphenyl, 2,5-diphenyloxazole, 1,4-bis- (2-methylstyryl) -benzene, xanthine, coumarin, acridine,
A cyanine dye, benzophenone, phthalocyanine, aromatic amine, aromatic polyamine, a compound having a quinone structure and forming a complex in an excited state, polyacetylene, polysilane, or the like is used.

The organic compound thin film is used in the form of an amorphous, microcrystalline, amorphous including polycrystalline, polycrystalline or single crystal thin film. The thickness of the thin film is not particularly limited, but usually 50 to 5000
Å degree is adopted. Of course, other ranges can be used.

The organic compound thin film is formed by various physical or chemical thin film forming methods such as a vacuum evaporation method,
A sublimation method, a coating method, and the like are also effectively used.

In the present invention, an inorganic semiconductor thin film layer can be effectively used as a charge injection layer as an electron or hole injection layer. Further, an amine-based organic compound can also be used for the hole injection layer.

The inorganic semiconductor thin film layer is composed of one kind of inorganic semiconductor thin film or a laminated film of two or more kinds of inorganic semiconductor thin films. These are amorphous thin films, microcrystalline thin films, polycrystalline thin films,
A single crystal thin film, a thin film in which amorphous and microcrystals are intermingled, a laminated thin film thereof, an artificial lattice thin film, and the like are used.

Inorganic semiconductor materials useful for forming these thin films include C, Ge, S
Primary semiconductors such as i and Sn, binary IV-IV semiconductors such as SiC, AlSb, BN, BP, GaN, GaSb, GaAs, GaP, InSb, InAs, InP
III-V group semiconductors such as CdS, CdSe, CdTe, ZnO, ZnS, ZnSe
And multi-component compound semiconductor materials. Specific examples of preferred material Si (silicon) include amorphous silicon (a-Si), hydrogenated amorphous silicon (a-Si: H), microcrystalline silicon (μc-Si), Polycrystalline silicon, single crystal silicon, hydrogenated amorphous silicon carbide (Si _1-X C _x : H), microcrystalline silicon carbide (μc-SiC), single crystal silicon carbide, amorphous silicon nitride, non-hydrogenated Amorphous silicon nitride, microcrystalline silicon nitride and the like are preferably used.

Here, the above-mentioned inorganic semiconductor thin film itself has p
It has a type or n-type property, or is doped and used as a p-type or n-type. In addition, the thickness is not particularly limited, but usually about 10 to 3000 mm is used. Of course, other things can also be used.

As a method for producing the above inorganic semiconductor thin film, there is a photo CVD method.
Various physical or chemical thin film forming methods such as a plasma CVD method, a thermal CVD method, a molecular beam epitaxy (MBE) method, an organic metal decomposition method (MOCVD), a vapor deposition method, and a sputtering method are used.

The two electrode layers in the present invention include metals, alloys,
A metal oxide, a metal silicide, etc., or one or two or more kinds of laminated thin films thereof are used. More preferably, a material having a high efficiency of injecting electrons or holes into the contacting thin film is selected.

As an example below, the order of a first electrode layer, an inorganic semiconductor thin film layer made of a p-type a-SiC: H thin film layer, an organic thin film layer which is a light emitting layer made of a metal complex and an extended conjugated quinone-based compound, and an order of a second electrode layer The element formed by the above will be specifically exemplified and described.

The first electrode layer is preferably made of an electrode material having a good hole injection efficiency into the p-type a-SiC: H semiconductor thin film. More specifically, as this electrode material, a metal compound thin film such as a metal, an alloy, or a metal oxide having a large electron work function, a conductive polymer material, a stacked thin film thereof, or the like is used. . Further, light generated from the first electrode can be extracted. To this end, the first electrode is formed of a transparent or translucent material. Specifically, a thin film of a metal oxide such as tin oxide (SnO ₂ ), indium oxide, indium-tin oxide (ITO), a laminated film thereof, Pt, Au, Se, Pd, Ni , W, Ta, Te and other metal and alloy thin films,
Alternatively, a laminated film thereof, a metal salt thin film of CuI or the like, a laminated film thereof, and the like can be given as preferable examples. Since the second electrode layer injects electrons into an organic thin film composed of a metal complex and an extended conjugated quinone-based compound, a metal or alloy thin film having a small electron work function, a laminated thin film thereof, or the like is generally used. Even more specifically, Mg, Li, Na,
K, Ca, Rb, Sr, alkali metals such as Ce, alkaline earth metals, rare earth elements, alloys such as Mg-Ag, Cs-O- Ag, Cs 3 S
Thin films such as b, Na ₂ KSb, (Cs) Na ₂ KSb, and a laminated thin film thereof are suitable.

The device of the present invention comprises an electrode layer / light-emitting layer / electrode layer / light-emitting layer /
The electrode layer / light emitting layer / electrode may be stacked in multiple stages. With this element structure, it is also possible to adjust the color tone and make the color multi-colored. In addition, this element may be arranged in a large number on a plane.
The elements arranged on this plane can also exhibit a function as a color display member by changing the emission color of each element or using an RGB filter.

[Comparative Example 1] An ITO film having a film thickness of 800 上 on a glass substrate, and further having a Sn film thereon
O ₂ film is formed to a thickness of 200 mm, a transparent conductive film (TCO) is formed,
This was the first electrode layer. Using a resistance heating vacuum evaporation method, an aluminum trisoxynate (Al (Ox) ₃ ) thin film, bisdihydrothiophenedylidenebisditertiarybutylbenzoquinone (in the structural formula 1, X = S, R = t-butyl group, n = 2) thin film, aluminum tris oxinate (Al (Ox) ₃ ) thin film
The light emitting layer was formed by depositing at 00 ° and 100 °. further,
A Mg thin film was deposited on this layer by an electron beam evaporation method to obtain a light emitting device of the present invention shown in FIG. 1 as a second electrode layer. The area of the deposited Mg metal film is 3 mm square.

When a DC voltage was applied to the light-emitting device, bright light emission that could be confirmed under an indoor fluorescent lamp was observed at 10 V or more. The light emission luminance was high, and a stable light emission state was maintained for a long time.

[Example 1] In Comparative Example 1, p-type a was provided between the first electrode and the light emitting layer.
A light emitting device shown in FIG. 2 was obtained in the same manner as in Comparative Example 1 except that -SiC: H150Å was formed.

In the present light emitting device, when the ITO side was plus and the Mg side was minus, the current increased with an increase in voltage, and a current did not flow with the opposite polarity, so-called diode characteristics were obtained. At a forward voltage application of 10 V, bright light emission was observed under an indoor fluorescent lamp. Light emission luminance was comparative example 1.
And the decrease in luminance over time was small.

[Comparative Example 2] In Comparative Example 1, an electrode having a laminated structure in which thiophene was subjected to electric field polymerization to obtain polythiophene was used on the first electrode. Further, as a light emitting layer on the first electrode, dihydrothiophenedylidenebisditert-butylbenzoquinone (in the structural formula 1, X = S, R = t-butyl group, n =
1) Thin film, aluminum trisoxynate (Al (Ox)
₃ ) The films were deposited at a film thickness of 200 ° and 100 ° in the order of thin films. Except for this, the light-emitting device of the present invention was manufactured in the same manner as in Comparative Example 1.

At a forward voltage of 12 V, bright light emission was observed under an indoor fluorescent lamp. The emission luminance was almost the same as that of Comparative Example 1, and the decrease in luminance with the passage of time was small.

〔The invention's effect〕

The present invention provides an injection-type EL element that operates by injecting electrons from one electrode and holes from the other electrode, in which the light-emitting layer includes an organic compound thin film including an extended conjugated quinone-based compound, preferably a light-emitting layer. By using a light emitting function expressing layer composed of an organic compound thin film composed of a metal complex and an extended conjugated quinone compound, an EL device having sufficient light emitting luminance and stable light emitting luminance can be obtained. As is clear from the examples, the injection type light emitting device according to the present invention is a light emitting device having high performance which could not be attained in the prior art, and is industrially extremely useful as a display member or the like.

[Brief description of the drawings]

FIG. 1 and FIG. 2 are explanatory diagrams showing an example of the layer structure of the light emitting device of the present invention. In the figure, 1,11 ... a substrate such as a glass plate, 2,12 ... a first electrode layer composed of a TCO thin film, etc., 3,13 ... a light emission composed of a metal complex and an organic compound thin film of an extended conjugated quinone compound. Layers 4, 14,..., Second electrode layer made of Mg metal thin film, etc., 15... P-type a-SiC: H
The charge injection layer is made of an inorganic semiconductor thin film layer.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C09K 11/06 CA (STN) REGISTRY (STN)

Claims (2)

(57) [Claims] A light emitting layer having an organic compound layer comprising a quinone compound represented by the general formula (1) between two electrode layers and a p-type hydrogenated amorphous SiC (p-type a-SiC: H A light emitting device comprising a charge injection layer comprising: (In the formula (1), X is selected from oxygen (O), sulfur (S), and selenium (Se) atoms, and R is hydrogen, methyl, ethyl, propyl, tertiary butyl, methoxy, Ethoxy, halogen, phenyl, hydroxy (O
H) group, mercapto (SH) group, amino group, n
Is an integer of 1 to 4. ) 2. The light emitting device according to claim 1, wherein a metal complex is mixed or laminated with an organic compound layer made of a quinone-based compound.