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Proceedings Paper

Materials and modeling for organic light-emitting diodes
Author(s): J. Campbell Scott; Sue A. Carter; Siegfried Karg; Marie Angelopoulos
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Paper Abstract

Polymer light-emitting diodes, based for example on MEH-PPV, are known to be susceptible to oxidative degradation. This leads to loss of conjugation, i.e. lower carrier mobility and higher operating voltage, and to the formation of carbonyl species, i.e. to luminescence quenching. In-situ FTIR has revealed that ITO can act as the source of oxygen. In order to explore further the mechanism of oxidation and to provide guidance for its elimination, we have studied the behavior of MEH-PPV LEDs prepared with a variety of conducting polymer anodes including polyaniline and polythiophene derivatives cast from various solvents and with various molecular and polymeric dopants. In all cases examined, it is found that polymer anodes lead to significant improvement in lifetime over devices with ITO as the anode contact. Moreover, in contrast to the variability observed for ITO anodes, conducting polymers with polymers with polymeric dopants yield consistently good devices with power efficiencies of about 0.5 percent at 5 volts and brightness in excess of 1000 cd/m2. Anodes prepared with small molecule dopants are more variable and exhibit short term behavior which suggests interfacial electrochemistry. We describe the device characteristics in the context of a model of hole-dominated bipolar charge injection with Langevin recombination.

Paper Details

Date Published: 4 April 1997
PDF: 6 pages
Proc. SPIE 3002, Light-Emitting Diodes: Research, Manufacturing, and Applications, (4 April 1997); doi: 10.1117/12.271028
Show Author Affiliations
J. Campbell Scott, IBM Almaden Research Ctr. (United States)
Sue A. Carter, Univ. of California/Santa Cruz (United States)
Siegfried Karg, Univ. Bayreuth (Germany)
Marie Angelopoulos, IBM Thomas J. Watson Research Ctr. (United States)

Published in SPIE Proceedings Vol. 3002:
Light-Emitting Diodes: Research, Manufacturing, and Applications
E. Fred Schubert, Editor(s)

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