Polythiophene, Electrochemical Doping and Photoexcitation

Abstract Absorption spectra, electrical conductivity and ESR of polythiophene during electrochemical cycles are studied. The existence of a shallow polaron is proposed below the doping level of 3 mol%. Drastic change of conductivity is conjectured to the shallow polaron which is also induced by the photoexcitation. The evolution of gap states at intermediate doping levels is consistent with the picture of polaron → bipolaron.