Electronic processes at interfaces involving conducting polymers

Abstract

We present quantum chemical calculations based on self-consistent molecular dynamics to discuss the processes involved in electroluminescence of conducting polymers (especially trans-polyacetylene (t-PA)). Specifically addressed are issues of finite and variable chain length, and of the charge transfer needed to make the chemical potential for the polymer and the metal Fermi energy equal, a necessary preliminary to calculations of injection dynamics. We examine the effects of the image interaction of carriers with a metal electrode, including the self-consistent prediction of the bonding pattern. Dynamic calculations include carrier mobilities obtained from computer experiments with an applied electric field, and initial studies of the evolution of two oppositely charged polarons into an exciton. There is a complex link between the behaviour of single polymer chains and descriptions of the polymer as a bulk semiconductor. One significant emerging issue concerns the fraction of polymer molecules contributing to electroluminescence. We comment on what can be learnt about the nature of the contact from scanning probe microscopies. A second major issue concerns the nature of the non-radiative processes competing with luminescence and the way this might be influenced.