The polaron and bipolaron contributions to the electronic structure of polypyrrole films

UPS and NEXAFS spectroscopy have been used to study the changes in the elec tronic structure of polypyrrole films by varying the dopant anion. In parti cular, we find the density of states within the electronic gap to be influe nced by the chemical structure of the dopant anion. From the position of th e Fermi level in the bandgap, the charge carriers in the polymer can be ide ntified either as polarons or as bipolarons. For the first time, we used co pper phthalocyanine trisulfonate as dopant, resulting in a high concentrati on of bipolarons which have a high contribution from the wavefunctions of t he pyrrole-nitrogen atoms. Interaction of the pi-systems of the polymer and the dopant causes a change in the chemical nature of the nitrogen from ami no-like to imino-like. (C) 1999 Elsevier Science B.V. All rights reserved.