Exciton dissociation and charge photogeneration in pristine and doped conjugated polymers

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)