Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
1998-06-11
2001-02-27
Yamnitzky, Marie (Department: 1774)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S917000, C313S504000
Reexamination Certificate
active
06194089
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an organic electroluminescent (EL) device and more specifically to, the organic medium in the organic EL device.
BACKGROUND OF THE INVENTION
Organic electroluminescent (EL) devices are generally composed of three layers of organic materials sandwiched between transparent and metallic electrodes, the three layers including an electron transporting layer, an emissive layer and a hole transporting layer. Organic EL devices are attractive owing to the requirement for low driving voltage and the potential application to full color flat emissive displays. Though significant lifetime has been achieved in the prior art (See U.S. Pat. No. 4,720,432), further improvement is needed for applications where high brightness is required. Among other things, the lifetime of an organic EL device is affected by the stability and reliability of both the bulk morphology of the hole transporting materials and the interface between the hole and electron transporting layers when the organic EL device is under bias.
Several schemes have been proposed to address the problem of bulk morphology stability of the hole transporting materials in an organic EL device: one being a double-layer hole transporting configuration (see U.S. Pat. No. 5,256,945); and another being usage of materials of high glass transition temperatures (U.S. Pat. No. 5,061,569).
It is a purpose of this invention to address the problem of the interface stability and reliability between heterojunctions in an organic EL device.
It is another purpose of this invention to provide a new method to enhance the thermal stability and reliability of the organic electroluminescent medium of an organic EL device.
It is a further purpose of this invention to provide an organic electroluminescent device for displays with improved reliability.
SUMMARY OF THE INVENTION
The above problems and others are at least partially solved and the above purposes and others are realized in an organic EL device including a cathode, an organic electroluminescent layer and an anode, laminated in sequence, wherein said organic electroluminescent layer is composed of a continuous organic medium without heterojunctions and which includes a component of hole injecting material.
According to the present invention, there is obtained an organic EL device with an improved reliability by eliminating the heterojunctions, and suppressing the aggregation or re-crystallization tendency of organic materials with the formation of a single layer of an organic mixture. Further, the reliability is increased by including a component of hole injecting material in the single layer of organic material. The component of hole injecting material can either be graded throughout the layer with the maximum amount appearing adjacent the anode terminal or the hole injecting material can be introduced in a uniform amount throughout the single layer.
REFERENCES:
patent: 5540999 (1996-07-01), Yamamoto et al.
patent: 5674597 (1997-10-01), Fujii et al.
patent: 5804322 (1998-09-01), Shi et al.
patent: 5811834 (1998-09-01), Tamano et al.
patent: 5925980 (1999-07-01), So et al.
Choong Vi-en
Lee Hsing-Chung
Shi Song Q.
Koch William E.
Motorola Inc.
Parsons Eugene A.
Yamnitzky Marie
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