JP3247148B2 - Electroluminescence element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroluminescent device provided with a light emitting layer in which a substance which emits light by current injection is formed in a layer shape by utilizing the electroluminescence of the substance.

[0002]

2. Description of the Related Art Such electroluminescent devices can be classified into a dispersion type and a thin film type when classified according to the light emitting layer structure for emitting light. In addition, when the electroluminescent elements are classified according to the light emitting layer material that emits light, they are classified into inorganic electroluminescent elements having an inorganic light emitting layer made of an inorganic substance and organic electroluminescent elements having an organic light emitting layer made of an organic substance.

For example, in an organic electroluminescence device, as shown in FIG. 1, two organic functional layers, a light emitting layer 3 and a hole transport layer 4 are sequentially formed between a pair of metal cathodes 1 and a transparent anode 2. There is a two-layer structure with a film. In addition, as shown in FIG.
It has a three-layer structure in which three organic functional layers, an electron transport layer 5, a light emitting layer 3, and a hole transport layer 4 are sequentially formed. In each case, a transparent anode 2, a hole transport layer 4, a light emitting layer 3, and an (electron transport layer 5,) cathode 1 are sequentially laminated on a glass transparent substrate 6. When a voltage is applied between the pair of electrodes, an exciton is generated by recombination of electrons injected from the cathode and holes injected from the transparent anode, and the exciton emits light in the process of radiation deactivation, This light is emitted outside through the transparent anode and the glass plate.

[0004]

However, even in the conventional organic electroluminescence device, light is applied from the transparent substrate side by applying a voltage to organic functional layers such as a hole transport layer, an organic light emitting layer and an organic electron transport layer. , There is a problem that the contrast is remarkably reduced due to reflection of external light from the metal cathode. The same applies to the inorganic electroluminescent element.

An object of the present invention is to solve the above-mentioned conventional problems, and an object of the present invention is to provide an electroluminescent device having improved contrast.

[0006]

An electroluminescent device according to the present invention has a light emitting layer that emits light by current injection, and at least one pair of transparent or translucent electrodes that face each other with the light emitting layer interposed therebetween. A light absorption / diffusion layer is provided outside one of the electrodes.

[0007]

According to the present invention, an electroluminescent device having a high contrast can be obtained.

[0008]

Embodiments of the present invention will be described below with reference to the accompanying drawings. As shown in FIG. 3, an organic electroluminescent device as an embodiment of the present invention comprises a light emitting layer 3 and a hole between a pair of transparent or translucent cathodes 1 and anodes 2 on a transparent glass substrate 6. It has a structure in which the transport layers 4 are sequentially formed, and a black light absorption / diffusion layer 7 is provided outside the transparent anode 2. The light transmittance of the cathode 1 can be controlled by the film thickness. The light absorption / diffusion layer 7 may be provided on the outermost side of the transparent glass substrate 6 as shown in FIG. 3A, or the outer side of the transparent glass substrate 6 which is in contact with the anode 2 as shown in FIG. May be provided. Furthermore, in these cases,
An uneven shape 8 may be provided at the interface between the light absorption / diffusion layer 7 and the transparent substrate 6 or the anode 2 to improve the light diffusion effect. Further, as shown in FIG. 3C, it is also possible to use a light absorption / diffusion layer substrate 7a by adding a light diffusion material such as mica to the transparent substrate itself. Although not shown, both the anode and the cathode may be transparent or translucent, and a light absorbing / diffusing layer made of only an uneven shape such as ground glass may be provided on one of the electrodes, and light may be extracted from the opposite electrode.

As described above, in the organic electroluminescence device having a two-layer structure of this embodiment, the cathode is made transparent or translucent, the light absorption / diffusion layer is provided on the anode side, and light is extracted from the cathode side. The same thing can be said for a three-layer structure if an electron transport layer is disposed between the above-described cathode and light-emitting layer. Further, for the cathode 1, a metal having a small work function such as aluminum, magnesium, indium, silver, or an alloy of each may be used. The anode 2 is made of a conductive material having a large work function, for example, indium tin oxide (IT
O), gold or the like. When gold is used as an electrode material, the electrode is in a translucent state. Further, a triphenylamine derivative or the like is used for the hole transport layer.
For the light emitting layer, Al oxine chelate, tetraphenylbutadiene derivative or the like is used. An oxadiazole derivative or the like is used for the electron transport layer.

Next, as shown in FIG. 4, the organic electroluminescent device of the second embodiment is substantially the same as the organic electroluminescent device having the structure shown in FIG. 1 or 2, but is transparent or translucent. It has a structure in which a black light absorption / diffusion layer 7 is provided outside the cathode 1. An uneven shape 8 can be provided at the interface between the light absorption / diffusion layer 7 and the cathode 1 to improve the light diffusion effect. As described above, in the organic electroluminescence device having the two-layer structure of the second embodiment, the cathode is made transparent or translucent, the light absorption / diffusion layer is provided outside the cathode, and light is extracted from the anode.

That is, as the light absorption / diffusion layer 7, a black film having high light absorption such as a carbon vapor deposition film obtained by a carbon arc method or the like can be used. By providing the light absorption / diffusion layer structure as described above, most of the light is absorbed when the light is applied to the light absorption / diffusion layer structure, so that the contrast on the viewing side can be improved.

[0012] In addition to the above organic electroluminescent element, the structure of the light absorption / diffusion layer can be applied to an inorganic electroluminescent element. As an inorganic electroluminescent element, a plurality of transparent electrodes such as ITO, a first insulating layer, a light emitting layer, a second insulating layer, and a plurality of back electrodes crossing the transparent electrodes are formed on a transparent glass substrate having a light absorbing and diffusing layer. They may be laminated and formed in order. The inorganic light emitting layer is Zn
It is preferable to use a layer containing several percent of a luminescent center substance using a semiconductor substance of a metal compound such as S, ZnSe, CaS, or SrS as a base substance. For example, when ZnS is used as a host substance, red light emission is exhibited when the emission center substance is Sm, and M
n emits yellow light, Tb emits green light, and Tm emits blue light.

[0013]

As described above, according to the electroluminescent device of the present invention, the light emitting layer which emits light by applying current and at least one pair of transparent or translucent electrodes which face each other with the light emitting layer interposed therebetween are provided. And the light absorption / diffusion layer on one outside of the electrode, so that the contrast can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic structural view of a conventional organic electroluminescence element.

FIG. 2 is a schematic structural view of a conventional organic electroluminescence element.

FIG. 3 is a schematic structural diagram of an organic electroluminescence element of an example.

FIG. 4 is a schematic structural view of an organic electroluminescence device according to a second embodiment.

[Explanation of Signs of Main Parts]

 DESCRIPTION OF SYMBOLS 1 Cathode 2 Anode 3 Light emitting layer 4 Organic hole transport layer 5 Organic electron transport layer 6 Glass substrate 7 Light absorption diffusion layer

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H05B 33/00-33/28

Claims (1)

(57) [Claims] 1. An anode is provided on a substrate, and light is emitted by current injection.
And a plurality of organic layers including a light-emitting layer comprising an organic compound.
Organic light-emitting device in which a cathode and a cathode are sequentially laminated
A sensing element, wherein the cathode is a transparent or translucent electrode.
An organic electroluminescence device , wherein the substrate outside the anode has a light absorption / diffusion layer.