Geminate charge pair recombination in sensitized photoconducting polymer

Recombination kinetics of the geminate charge pairs, generated by photoexcitation of charge transfer (CT) complexes in sensitized poly-N-epoxypropylcarbazole, have been investigated by transient absorption and time-resolved fluorescence techniques and modeled by Monte Carlo method. The quantitative agreement of simulations with experimental data is obtained by assuming the distance between the thermalized charge pairs to be several times longer than the typical distance between electron donor and acceptor in CT complexes. Faster recombination is observed in the films with higher sensitizer concentrations and explained by assuming that electron acceptor molecules act as scattering centers for hole motion during thermalization, thus reducing the thermalization distance. The dynamical blue shift of the fluorescence band and comparison of hole density with fluorescence kinetics suggest that heterogeneity of CT complexes results in different radiative probabilities and in distribution of the initial charge pair separation distances. (C) 1999 American Institute of Physics. [S0021-9606(99)51236-1].