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Proceedings Paper

Conduction and trapping in electroluminescent polymer devices
Author(s): Alasdair J. Campbell; Michael S. Weaver; David G. Lidzey; Donal D. C. Bradley; Ekkehard Werner; Wolfgang Bruetting; Markus Schwoerer
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Paper Abstract

The current-voltage characteristics of ITO/polymer film/Al or Au devices of poly(phenylene vinylene) (PPV) and a dialkoxy PPV copolymer can be fitted at high applied bias to a power law of the form J equals KVm where m increases with decreasing temperature, log(K) is proportional to m, and K is proportional to d-(alpha m) where d is the film thickness and (alpha) is a constant. (alpha) 2 and 1 for the Al and Au cathode devices respectively. Different single carrier space charge limited conduction (SCLC) theories, including either an exponential trap distribution or a hopping transport field and temperature dependent mobility, are used to try and explain this behavior. Both models are in good agreement with the general experimental results, but can also be criticized on a number of specific issues.Mixed SCLC models and the effect of dispersive transport are also explored. It is concluded that carrier mobility and trap measurements are required to distinguish between these models. To this end, initial trap measurements of ITO/PPV/Al devices using deep level transient spectroscopy (DLTS) are reported. Very deep positive carrier transport with emptying times > 4 minutes have been detected. The non-exponential DLTS transients have been successfully modeled on an isoelectronic trap level emptying to a Gaussian distribution of transport states, with a trap depth and density of 0.8eV and 4 by 1016 cm-3 respectively.

Paper Details

Date Published: 16 December 1998
PDF: 13 pages
Proc. SPIE 3476, Organic Light-Emitting Materials and Devices II, (16 December 1998); doi: 10.1117/12.332603
Show Author Affiliations
Alasdair J. Campbell, Univ. of Sheffield (United Kingdom)
Michael S. Weaver, Univ. of Sheffield (United States)
David G. Lidzey, Univ. of Sheffield (United Kingdom)
Donal D. C. Bradley, Univ. of Sheffield (United Kingdom)
Ekkehard Werner, Univ. Bayreuth (Germany)
Wolfgang Bruetting, Univ. Bayreuth (Germany)
Markus Schwoerer, Univ. Bayreuth (Germany)

Published in SPIE Proceedings Vol. 3476:
Organic Light-Emitting Materials and Devices II
Zakya H. Kafafi, Editor(s)

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