Exciton dissociation and charge photogeneration in pristine and doped conjugated polymers

Abstract

There is abundant experimental and theoretical evidence of the fact that the primary optical excitation in conjugated polymers is a singlet exciton with a binding energy of typically 0.5 eV. In the absence of excess photon energy, free or geminately bound charge carriers (polarons) have to be generated from relaxed excitons via a secondary dissociation process. This process requires further excitation of several tenths of eV in order to compensate for the exciton binding energy. Concomitantly, exciton breaking can occur either in a strong external electric field or via charge transfer to an electron or hole scavenger. Experimentally, these processes are revealed in field- and dopant-assisted photoluminescence quenching, photoinduced optical absorption, and photoconductivity. Experimental and theoretical aspects of these phenomena are reviewed in the present article. © 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.