JPH03105898A - Organic el device - Google Patents

Abstract

PURPOSE:To prevent light emitting efficiency from lowering, driving voltage from increasing, and a service life from shortening by composing a hole transporting layer and an electron transporting layer with a P-type amorphous semiconductor and an n-type amorphous semiconductor, respectively. CONSTITUTION:A material with high work function is used for a hole injection electrode 2 which is formed on a glass substrate 1 and ITO is used as the material. A hole transporting layer 3 to be formed on the ITO electrode is composed with a P-type amorphous semiconductor and an organic phosphor layer 4 is composed with 8-hydrooxyquinoline aluminum (Alq3) and then an electron transporting layer 5 to be formed on the phosphor layer is composed with an N-type amorphous semiconductor and an electron injection electrode 6 to be formed finally is obtained by MgAg deposition. Like this, the hole transporting layer 3 and the electron transporting layer 5 are composed with a P-type amorphous semiconductor and an n-type amorphous semiconductor, respectively. As a result, without increasing driving voltage and lowering light emitting efficiency, a long service life is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial Application Field The present invention relates to an mEL (electroluminescence) device.

(b) Conventional technology Inorganic EL devices and organic EL devices are known as EL devices. Inorganic EL X-ray elements are of the collision type EI, ie, excitation-emission type due to the collision between accelerated electrons and luminescent centers, whereas organic EL elements are of the injection type, ie, the emission type due to recombination of electrons and holes. Due to the difference in the light emitting principle between the two, the driving voltage of the inorganic EL element is 100 to 200V, whereas the organic EL element is superior in that it has a low driving voltage of about 10 to 20V. In addition, for organic EL elements,
By selecting fluorescent materials, three primary color light emitting elements can be
It is expected that a full-color display device will be realized.

However, although the @E Lll child has such advantages, it still has various technical problems that need to be solved.

Currently, the mainstream of research is C. W. Ta
ngetal. Appl. Phys. Lett. V
ol. 51. No. 12. 913 (1987)
The two-layer structure shown in C. Adachi etal,
J. J. A. P. Vol1. 27, No. 2, L
269 (1988).

A typical three-layer structure consists of a glass substrate (
1) On top, hole injection electrode (2), hole transport layer (3)
, an organic phosphor layer (4), an electron transport layer (5), and an electron injection electrode (6) are sequentially laminated, and in particular, a hole transport layer (3), an organic phosphor layer (4), and an electron transport It is called a three-layer structure because it has a three-layer junction of layer (5). Note that the two-layer structure has a two-layer junction of a hole transport layer and a light emitting layer, and lacks an electron transport layer.

(c) Problems to be Solved by the Invention In the conventional two-layer structure and three-layer structure, the hole transport layer and the electron transport layer are composed of organic thin films. It is difficult to obtain a uniform film due to precipitation, etc. For this reason, the produced EL device has drawbacks such as a decrease in luminous efficiency, an increase in driving voltage, and a decrease in life. The present invention therefore seeks to overcome such drawbacks.

(2) Means for Solving the Problems In the organic EL device of the present invention, in the two-layer structure or the three-layer structure, the hole transport layer and the electron transport layer are respectively composed of a p-type amorphous semiconductor and an n-type amorphous semiconductor. It is characterized by

(e) Function Amorphous semiconductors have better film formation conditions than organic thin films,
Provides a uniform film.

(F) Embodiment An embodiment of the present invention will be explained using a three-layer structure shown in FIG. Glass substrate (1). A hole injection electrode shaped as h (
As for 2), a material with a large work function such as gold or ITO (indium-tin oxide) is used as in the past, and in this embodiment, ITO with a thickness of 100 mm was used.

The next deposited hole transport layer (3) is comprised of a P-type amorphous semiconductor, which is a feature of the present invention. This semiconductor is formed by a plasma reaction caused by glow discharge, and is typically amorphous silicon (hereinafter abbreviated as a-Si) and amorphous silicon carbide C (hereinafter abbreviated as a-SiC). In this example, a-Si is used in terms of high light transmittance.
C was used, and its film thickness was 500A. P type a-
More specifically, SiC is Si}1s'CH<:B*
It was formed using a glow plate electrode using a mixed gas of L-50'50'0.5 as a reactant gas.

The organic phosphor layer (4) is made of g-hydroox as before.
y quinoline aluminum (hereinafter referred to as A
(abbreviated as lqs) and had a depth of 400 people. The manufacturing method of Ajqg is as described above in C. W. Tang eta
As detailed in the literature, it is formed by a vacuum evaporation method, and the conditions at that time are: degree of vacuum: 10-'Torr, substrate temperature:
At room temperature, the deposition rate was 1-3 A/sec.

The subsequently deposited electron transport layer (5) is filled with an n-type amorphous semiconductor as a feature of the invention.

This semiconductor is shaped similarly to the hole transport layer (3),
More specifically, it is formed by glow discharge using PH,:Si}1♂1:100} combination gas as the reaction gas,
It was made of n-type a-Si with a thickness of 0.

The electron injection t-pole (6〉) formed last is the same as before.
It was obtained by depositing MgAg by 300 people using co-evaporation method.

When a DC voltage of 20 V was applied between the hole injection electrode (2) and the electron injection electrode (6>) in the organic EL device manufactured in this way, a luminance of 900 Cd/m' was observed. , the same green color as A'qs's fluorescence,
As shown in FIG. 2, the spectrum was broad centered at 550 nm. In addition, the half-life of brightness was 70 hours, which significantly extended the lifespan compared to the conventional method (about 10 hours).

The present invention is applicable not only to a three-layer structure but also to a two-layer structure. In that case, a P-type amorphous semiconductor is used as the hole transport layer, more specifically P-type a-Si or a-S.
iC, preferably P-type a-SiC, is suitable.

(G) Effects of the Invention According to the present invention, the quality of the hole transport layer and the electron transport layer is improved in organic EL devices having a two-layer structure or a three-layer structure, thereby preventing an increase in driving voltage and a decrease in luminous efficiency. It has now been possible to extend the lifespan without any problems.

[Brief explanation of drawings]

Fig. 1 is a side view for explaining an embodiment of the present invention;
The figure is an emission spectrum diagram of the same example. (3)...Hole transport layer, (4)...Organic phosphor layer, (5)...Electron transport layer.

Claims (1)

[Claims] (1) In the structure in which a hole transport layer and/or an electron transport layer are bonded to an organic phosphor layer, the hole transport layer and the electron transport layer are respectively made of a P-type amorphous semiconductor and an n-type amorphous semiconductor. Organic EL element.