Deep defect levels and exciton dissociation in conjugated polymers

Abstract

We study the localized deep electronic level within the bandgap of conjugated polymers in the presence of structure or oxygen (carbonyl group) defects. The structure defect is modeled as a chain twist, including the chain ends as a special case. Analytic expressions for both the energy and the wavefunction of the deep levels and the itinerant levels are obtained and supplemented by clear intuitive pictures. Carbonyl group is treated numerically within the tight-binding models. The rates of free carrier capture and exciton dissociation through the defect level via multi-phonon emission are calculated. We conclude that the defect dissociation dominates the intrinsic dissociation through thermal activation, and is the primary carrier generation mechanism in photoconductivity, Our results explain the photoconductivity enhancement due to oxidation, as well as the recent observation on the temperature-independent photocurrent in the sweep-out regime. (C) 2001 Elsevier Science B.V. All rights reserved.