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Improvement of Power Efficiency in Organic Electroluminescent Devices

Published online by Cambridge University Press:  15 March 2011

Chimed Ganzorig  and
Masamichi Fujihira
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

In order to improve power efficiency of organic electroluminescent (EL) devices, i.e., ITO/TPD/Alq3/Al, enhanced electron and hole injection at Alq3/Al and ITO/TPD interface, respectively, was attempted by designing proper charge injection at both interfaces. Enhanced charge recombination at TPD/Alq3 was also demonstrated. Here, ITO, TPD, Alq3, and Al are abbreviations for indium-tin-oxide, N,N'-diphenyl-N,N'-bis(3-methyl-phenyl)-1,1'-biphenyl-4,4'-diamine, tris(8-hydroxyquinoline) aluminum, and metal aluminum, respectively. Enhanced electron injection by introducing a thin layer of Li salts of fluoride, acetate, and benzoate was described. We have found that the electron injection was improved in the order of Li+, Na+, K+, Rb+, and Cs+, and Cs salts exhibited the best EL performance. Chemical modification of ITO has been attempted to fine-tuning the work function of ITO in order to reduce hole injection barrier height. EL characteristics were improved dramatically using ITO modified with H-, Cl-, and CF3-terminated benzoyl chlorides. By using reactive -COCl groups, ITO surfaces were covered quickly and the work function of ITO was changed widely depending upon permanent dipole moments introduced in para-position of benzoyl chlorides. Correlation between the change in the work function of ITO and the EL characteristics was examined. The improvement of charge recombination was attained by increasing the interfacial areas, i.e. introducing a mixed layer of TPD and Alq3, or inserting a thin film of rubrene with a higher recombination efficiency.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 708: Symposium BB – Organic Optoelectronic Materials, Processing and Devices , 2001 , BB3.21
Copyright
Copyright © Materials Research Society 2002

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References

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