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Proceedings Paper

Influence of conductivity and work function of polyaniline-based HIL on PLED device performance
Author(s): Joerg R. Posdorfer; Bettina Werner; Bernhard Wessling; Susanne Heun; Heinrich Becker
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Paper Abstract

Polyaniline (PAni) dispersions can be efficiently used as hole injection layers (HIL) for passive and active matrix display applications. In earlier work the influence of conductivity and work function of HILs spin coated from water based PAni/PSS dispersions on device performance had already been presented. Recent investigations on hole transport mechanism in polyaniline systems now show the necessity of a minimum conductivity and an optimum work function for hole injection. Electrochemical Impedance Spectroscopy measurements combined with luminescence investigations showed that the lateral conductivity in the PAni films must be >10-6 S/cm. Otherwise, a decrease in maximum efficiency and an increase in driving voltage in dependence on coating thickness occurs. Work function investigations on water-free, highly conductive polyaniline dispersions emphasize the theory of an optimum range for hole injection from the anode into the light emitting polymer. The work function of highly conductive, non-aqueous PAni dispersion (0.1-5 S/cm) was determined by Scanning Kelvin Probe method to be 4.5 - 4.7 eV, which is outside of the optimum range at about 4.95 - 5.05 eV for polymeric light emitting diodes, resulting in poor efficiency values (max. 30 - 50% compared to PAni/PSS standard).

Paper Details

Date Published: 16 February 2004
PDF: 9 pages
Proc. SPIE 5214, Organic Light-Emitting Materials and Devices VII, (16 February 2004); doi: 10.1117/12.510006
Show Author Affiliations
Joerg R. Posdorfer, Ormecon GmbH (Germany)
Bettina Werner, Ormecon GmbH (Germany)
Bernhard Wessling, Ormecon GmbH (Germany)
Susanne Heun, Covion Organic Semiconductors GmbH (Germany)
Heinrich Becker, Covion Organic Semiconductors GmbH (Germany)

Published in SPIE Proceedings Vol. 5214:
Organic Light-Emitting Materials and Devices VII
Zakya H. Kafafi; Paul A. Lane, Editor(s)

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