JP3137631B2 - 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
The light-emitting element has a structure in which a layer (light-emitting layer) exhibiting the above light-emitting function is arranged between two electrodes, and converts electric energy directly into light by applying a voltage between the electrodes. 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 and fluorescent lamps, various shapes such as thin-film panels, belts, and cylinders, for example, display members for lines, diagrams, 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. Recently, an injection-type light emitting diode device in which two organic compound thin films having hole conductivity and electron conductivity are stacked (CWTan).
g: Appl. Phys. Lett., 51 (12) , (1987) 193). Light-emitting elements using such organic materials have attracted attention because of their features such as various thin film formation methods and the ability to form thin films with a large area with high accuracy.

However, when an element is formed using only the organic materials for EL known at present, the intensity of light emission is limited to some extent, and there are problems such as instability of the light emission intensity. Therefore, there is a strong demand for an EL element that can produce a large-area and uniform thin film, has high mass productivity, and is advantageous in terms of cost. In this regard, the present inventors have proposed in Japanese Patent Application No. 63-292467 a light-emitting device in which a charge injection layer composed of an inorganic semiconductor thin film and a light-emitting layer composed of an organic compound are laminated between electrodes.

The present inventors have further studied and found a light-emitting element having more excellent durability, which is disclosed herein.

[Disclosure of the Invention]

That is, the present invention includes two electrode layers,
A light-emitting element having a light-emitting layer having an organic compound thin film layer mainly containing an organic complex compound of a rare earth metal between two electrode layers. Preferably, a charge injection layer is provided between the two electrode layers. A light-emitting element having a structure in which the light-emitting elements are stacked.

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

FIG. 1 shows one embodiment. 2
The light-emitting element includes two electrode layers 2 and 4, and a light-emitting layer having an organic compound thin film layer 3 mainly containing an organic complex compound of a rare earth metal is provided between the two electrodes 2 and 4. FIG. 2 shows another embodiment of the present invention.
The organic compound thin film layer 13 and the charge injection layer 15 are provided between the layers 2 and 14. In FIG. 2, the electrode in contact with the charge injection layer 15 is the first electrode, and the organic compound thin film layer 13
The electrode in contact with is referred to as a second electrode.

The light emitting layer in the present invention is an organic compound thin film containing a rare earth metal organic complex compound.

Rare earth metals include yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), Terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Y
b), lutetium (Lu), but cerium (C
e), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu),
Terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), and ytterbium (Yb) are preferred. Divalent, trivalent or tetravalent ions of these metals are used.

Examples of the ligand of the organic compound include those having a β-diketone group such as acetylacetone, dibenzoylmethane, and 2-thenoyltrifluoroacetone; and carboxylic acids such as o-benzoylbenzoic acid, salicylic acid, and o-phthalic acid. Those having an acid group; those having a ketone group or aldehyde group adjacent to the hydroxyl group of salicylaldehyde, o-hydroxyacetophenone, or o-hydroxybenzophenone; oxines such as 8-hydroquinquinoline and 5,7-dibromooxin , 2.2'-bipyridine, 2,
There are pyridines such as 2 ', 2 "-tripyridine and 1,10-phenanthroline, and these ligands are used alone or in combination.

Further, in the present invention, having a high emission quantum efficiency,
It does not preclude the use of an organic compound having a π-electron system which is easily susceptible to external perturbation and which is easily excited when mixed with the above metal complex. Examples of the organic compound include condensed polycyclic aromatic hydrocarbons such as rubrene; p-terphenyl, 2,5-diphenyloxazole, 1,4-bis-
(2-methylstyryl) -benzene, xanthine, coumarin, acridine, cyanine dye, benzophenone, phthalocyanine, aromatic amine, aromatic polyamine, a compound having a quinone structure and forming a complex in an excited state, polyacetylene, polysilane, It is an organometallic complex.

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. As the hole-injection layer, an amine-based organic compound or a conductive polymer such as polypyrrole or polythiophene can be used.

As the inorganic semiconductor thin film layer in the present invention, 1
It is composed of a kind of inorganic semiconductor thin film or a laminated film of two or more kinds of inorganic semiconductor thin films. As these, an amorphous thin film, a microcrystalline thin film, a polycrystalline thin film, a single crystal thin film, a thin film in which amorphous and microcrystals are mixed, 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 a multi-component compound semiconductor material.

Here, specific examples of Si (silicon) as a preferable material include amorphous silicon (a-Si), hydrogenated amorphous silicon (a-Si: H), and microcrystalline silicon (μc).
-Si), polycrystalline silicon, single crystal silicon, hydrogenated amorphous silicon carbide (Si ₁ -xCx: H), microcrystalline silicon carbide (μc-Si
C), single-crystal silicon carbide, amorphous silicon nitride, hydrogenated amorphous silicon nitride, microcrystalline silicon nitride, and the like are preferably used.

The above-mentioned inorganic semiconductor thin film has a p-type or n-type property, or is doped to be 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-mentioned inorganic semiconductor thin film, a photo CVD
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. Hereinafter, when the layer configuration of the element is as shown in FIG. 2, for example, the first electrode layer, the p-type
-An inorganic semiconductor thin film layer composed of a SiC: H thin film layer, an organic thin film layer which is a light emitting layer composed of an organic complex compound of a rare earth metal,
The elements formed in the order of the second electrode layers 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 the electrode material, a metal compound thin film having a large electron work function, an alloy, a metal compound thin film such as a metal oxide, 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, and indium-tin oxide (ITO), a laminated film thereof, Pt, Au, Se, Pd, Ni , W, Ta, Te and other metal and alloy thin films,
Preferred examples thereof include a laminated film thereof, a metal salt thin film such as CuI, and a laminated film thereof.

Further, since the second electrode layer injects electrons into an organic thin film made of an organic complex compound of a rare earth metal, generally, a metal or alloy thin film having a small work function of electrons, a laminated thin film thereof, or the like is used. Even more specifically, Mg, Li, N
a, 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 multi-tiered. With this element structure, it is also possible to adjust the color tone and make the color multi-colored. Also, a large number of such elements may be arranged on a plane.
In the elements arranged on this plane, a desired function as a color display member can be exhibited by changing the emission color of each element or using an RGB filter.

 Hereinafter, the present invention will be described with reference to examples.

[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. Film thickness with terbium acetylacetonate (Tb (acac) ₃ ) using resistance heating vacuum evaporation
A light emitting layer of 600 mm was formed. Further, a Mg thin film was deposited on this layer by an electron beam evaporation method to obtain a light emitting device shown in FIG. 1 as a second electrode layer. The area of the deposited Mg metal film is 1 cm square.

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

[Comparative Example 2] An ITO film having a film thickness of 800 に on a glass substrate, and further having a Sn film
O ₂ film is formed to a thickness of 200 mm, a transparent conductive film (TCO) is formed,
This was the first electrode layer. A light emitting layer having a thickness of 600 mm was formed from a mixed thin film of terbium acetylacetonate (Tb (acac) ₃ ) and rubrene by using a resistance heating vacuum evaporation method. Furthermore, Mg is deposited on this layer by electron beam evaporation.
A thin film was deposited to obtain a light emitting device as shown in FIG. 1 as a second electrode layer. The area of the deposited Mg metal film is 1 cm square.

When a DC voltage was applied to this light-emitting device, bright yellow light emission was observed at 10 V or higher under an indoor fluorescent lamp. 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: H 150 ° 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 green light emission was observed under an indoor fluorescent lamp. The emission luminance was higher than in Comparative Example 1, and the decrease in luminance with the passage of time was very small.

[Example 2] In Comparative Example 1, the 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 2 except that -SiC: H 150 ° 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 yellow luminescence was observed under an indoor fluorescent lamp. The emission luminance was higher than in Comparative Example 1, and the decrease in luminance with the passage of time was very small.

Comparative Example 3 In Comparative Example 1, an electrode having a multilayer structure in which thiophene was subjected to electric field polymerization to obtain polythiophene was used on the first electrode. In addition, terbium acetylacetonate (Tb (acac) ₃ ) was deposited on the first electrode as a light emitting layer to a thickness of 600 °. 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 application of 12 V, bright green 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 very 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, by using a light-emitting function expression layer made of an organic complex compound of a rare earth metal as a light-emitting layer. The EL device has sufficient light emission luminance and stability of light emission luminance. As is clear from the examples, the injection type light emitting device according to the present invention is a high performance light emitting device that could not be reached in the prior art, and is said to be extremely useful industrially as a display member or the like. I have no choice.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an example of a layer configuration of a comparative example, and FIG. 2 is an explanatory diagram showing an example of a layer configuration of an element 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 emitting layer composed of an organic compound thin film of an organic complex compound of a rare earth metal, 4 , 14... A second electrode layer made of a Mg metal thin film or the like; 15... A charge injection layer made of a p-type a-SiC: H or other inorganic semiconductor thin film layer.

──────────────────────────────────────────────────の Continued on the front page (58) Fields investigated (Int. Cl. ⁷ , DB name) C09K 11/06 H05B 33/00 CA (STN) REGISTRY (STN) WPI (DIALOG) Patent file (PATOLIS)

Claims (2)

(57) [Claims] 1. A light emitting layer having two electrode layers, an organic compound thin film layer mainly containing an organic complex compound of a rare earth metal between these two electrode layers, and a p-type hydrogenated amorphous SiC (p-type a -SiC: H). A light-emitting element comprising a charge injection layer formed by stacking layers. 2. The light emitting device according to claim 1, wherein the rare earth metal organic complex compound is terbium acetylacetonate.