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Loss Process in Efficiency of Blue Organic Electroluminescent Devices

Published online by Cambridge University Press:  15 February 2011

Yasuo Enatsu ,
Chimed Ganzorig  and
Masamichi Fujihira
Yasuo Enatsu
Affiliation:
Department of Biomolecular Engineering, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8501, Japan
Chimed Ganzorig
Affiliation:
Department of Biomolecular Engineering, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8501, Japan
Masamichi Fujihira
Affiliation:
Department of Biomolecular Engineering, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8501, Japan
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Abstract

We report EL characteristics of blue organic electroluminescent (EL) devices with a hole transport layer (HTL) as an emitter i.e. ITO/NPD/BCP/Alq3/Cs(0.5 nm)/Al. Here, ITO, NPD, BCP, and Alq3 are abbreviations for indium-tin-oxide, 4,4'-bis[N-(1-naphthyl)-N-phenylamino]- biphenyl, 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline, and tris(8-hydroxyquinoline) aluminum, respectively. Three different chemically modified ITO electrodes were used. As a hole-injecting buffer layer, copper phthalocyanine (CuPc) or 4,4',4''-tris-(3-methylphenylphenylamino) triphenylamine (MTDATA) was used in this study. We found that the luminance increased less than linearly with an increase in current for all EL devices studied even when hole and electron injection were enhanced. The luminance loss in the device is attributed to quenching singlet excited states (1NPD*) by large excess radical cations (NPD+.) accumulated in the emission zone due to large overlap between a fluorescence spectrum of 1NPD* and an absorption spectrum of NPD+.. In addition, 1NPD* can be also quenched by radical anions (NPD-.) when excess electrons are injected.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 771: Symposium L – Organic and Polymeric Materials and Devices , 2003 , L4.38
Copyright
Copyright © Materials Research Society 2003

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