JPH01312873A - Organic thin film EL device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to organic thin film EL used for flat light sources and displays.
(Electroluminescent) device.

[Conventional technology]

EL devices made from organic materials have been studied as a means of realizing inexpensive, large-area, full-color display devices. However, conventional EL elements made from R-containing materials are ZnS:
Compared to Mn-based inorganic thin film El-elements, the luminance was lower and the characteristics deteriorated significantly, so it could not be put into practical use. However,
Recently, an organic thin film EL device with a two-layer organic thin film structure has been reported, and this device has attracted strong interest (Reference Applied Physics Letters, Vol. 51).

According to this document, a bright green light-emitting device is obtained by using a fluorescent metal chelate complex as an organic phosphor thin film layer and an amine-based material as a hole-conducting layer. Several 1 QOcd/rd when applying a DC voltage of ~7V
It has been reported that it has a luminance of 1.5 Qn/W, and a pot luminous efficiency of 1.5 Qn/W, which is close to a practical level of performance.

The structure of the organic thin film EL device is as shown in FIG. E! 22 and the back electrode 25, there is a hole injection layer 23 made of a low-molecular organic semiconductor material exhibiting hole conductivity, such as an amine type, and a metal chelate complex exhibiting electron conductivity and emitting strong fluorescence. It has a structure in which approximately 500 organic phosphor thin film layers 24 are laminated.

[Problem to be solved by the invention]

By the way, the organic thin 11! As mentioned above, the BL element has excellent initial characteristics. However, a very fast deterioration of the luminescent properties is a problem. For example, 51 in dry argon.
When driven with a constant current of ^/d, the initial value was 50Cd/
After 100 hours, the brightness that was d is 15-20 cd/rd.
It declined to . During the test, the applied voltage increased from 5.5V to 14V. Moreover, even if careful attention is paid to the device manufacturing process and the seal is sufficiently repaired, it is difficult to reduce the rate of deterioration of the characteristics.

For practical use as an EL element, it is necessary that the luminance half-life time be 1000 hours or more when a constant voltage is applied, for example.

An object of the present invention is to provide an organic thin +1QEL element that solves the above problems.

[Means to solve the problem]

In order to achieve the above object, the organic thin film EL device of the present invention has a laminated structure of an organic phosphor thin film layer and an inorganic semiconductor thin film layer exhibiting hole conductivity between a pair of electrodes, at least one of which is transparent. It has the following.

[Effect]

Conventional two-layer organic thin film 11 shown in Fig. 3! When the EL element was sufficiently sealed and the element was subjected to a knee zinc test in dry argon, deterioration in the form of a decrease in brightness and an increase in emission voltage occurred over several tens of hours as described above. As a result of investigating the cause of this deterioration, it was determined that it was mainly due to a decrease in hole injection efficiency from the hole injection layer.

The decrease in hole injection efficiency is caused by:
This is caused by deterioration of the hole injection layer material, which generally has poor heat resistance, due to Joule heat of around 2 W/d, and (2) an increase in the resistance of the hole injection layer due to the energization itself.

Although a current of about 10n+A/i is essential to obtain a practical level of luminance, it has been difficult to prevent deterioration of conventional organic thin film EL devices as long as organic hole injection layer materials are used.

Therefore, the hole-conducting type 9! has much better stability than the conventional organic hole-injection layer materials and has high hole concentration and mobility. #, we focused on mechanical semiconductor materials.

The present invention is based on the fact that an element with stable light-emitting properties can be obtained as a result of using a hole-conducting inorganic semiconductor as a hole-injection layer instead of a conventional organic hole-injection layer material. . S1+-xCx (
0≦X≦1) was practically excellent. An amorphous or microcrystalline S i +-x c8 thin film can be easily formed over a large area, and it is also easy to impart hole conductivity through doping. In addition, there is little change in electrical properties due to current flow or temperature, there is no electrochemical reaction with electrode materials, and furthermore, it has excellent translucency. In addition to 5it-xCx, Cul, CuS and G
Various P-type (hole conductive) semiconductor thin films can be used, including III-V, I[-Vl group compounds such as aAs and Zn'r'e.

Due to the structure of the present invention, P type! ! l! Holes are now injected into the organic phosphor thin film layer more stably than with the fi semiconductor thin film. Therefore, it is possible to provide an element with significantly higher reliability than the conventional one while taking advantage of the characteristics of an organic thin film EL element that is driven at a low voltage.

〔Example〕

The organic thin film EL device of the present invention will be described in detail below according to Examples.

In FIG. 1, first, a glass substrate 1 was prepared, on which approximately 2000 ITO (indium tin oxide) transparent electrodes 2, which were patterned into a suitable shape, were formed. This glass substrate 1 is thoroughly cleaned with acetone and pure water in a clean room.
A thin film layer 3 of i+-xcx (o≦X≦1) was formed. This thin film layer 3 has an electrical conductivity of 10-'10' S -ci-
It is a P-type semiconductor thin film of about . Film thickness is 100-100
An organic phosphor thin film layer 4 of 50 to 1,000 layers was formed on the surface of the zero layer, which was almost transparent. The material used here is a fluorescent metal quinoline chelate complex. Its chemical formula is shown in Figure 2.

After M, about 2000 silver/magnesium alloys were formed as the back electrode 5 by electron beam evaporation, and the surface was covered with a sealing cover 6 to complete the device.

By applying a DC voltage of about 10 V to this device with the transparent electrode (ITO) 2 side being positive and the silver/magnesium back electrode 5 side being negative, bright green light emission of about 500 cd/d could be obtained. In addition, when a constant voltage is applied, 10
After aging for 0 hours, the brightness decreased by 10
The stability was significantly improved.

Further, even at ambient temperature of 70''C, there was very little deterioration.

Incidentally, as the material forming the light-emitting layer, an organic compound exhibiting strong fluorescence can be used. For example, the quinoline chelate complex of aluminum shown in the example, copper, zinc (),
Quinoline complexes such as cadmium and magnesium, metal phthalocyanine lllii derivatives, etc., general condensed polycyclic compounds such as anthracene, naphthacene, and tetracene, and their derivatives can be used.9 The present invention does not limit the organic phosphor material used.

In addition, the inorganic hole injection layer material is not limited to 5in-xC, but may also include CuI, CuS, P type 1v group,
A thin film layer made of an inorganic semiconductor exhibiting hole conductivity due to an m-v group or I[-Vl group semiconductor thin film can be used.

In addition to silver-magnesium alloys, magnesium, indium, aluminum, tin, gold, and silver could be used for the electrodes.

However, in the case of gold electrodes, EL emission became weaker.

〔Effect of the invention〕

As explained above, the organic thin film El-element of the present invention has the following effects. That is, 1) There is almost no reduction in brightness compared to conventional organic thin film EL elements.

2) Compared to conventional organic thin 1[IEL elements, characteristics change due to ambient temperature are reduced.

3) The driving voltage could be lowered. This is because holes can now be effectively injected at low voltage. For example, a practical level of brightness was obtained even at DC6V.

As described above, the present invention makes it possible to improve organic thin film EL devices to a practical level, and has great industrial value.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a cross-sectional structure of an organic thin film EL device according to an example of the present invention, FIG. 2 is a diagram showing a chemical formula of a fluorescent metal quinoline chelate complex used in the present invention, and FIG. 3 is a diagram showing a conventional 1 is a diagram showing a cross-sectional structure of an organic thin film EL element. 1... Glass substrate 2... Transparent electrode 3 =
-P type S i + -x Cx thin film layer (inorganic semiconductor thin film layer exhibiting hole conductivity) 4...organic phosphor thin film layer
5... Back electrode patent applicant NEC Corporation Representative Patent attorney Uchihara Muka\, / Figure 3

Claims (1)

[Claims] (1) An organic thin film EL device characterized by having a laminated structure of an organic phosphor thin film layer and an inorganic semiconductor thin film layer exhibiting hole conductivity between a pair of electrodes, at least one of which is transparent.