Ultrafast relaxation dynamics of photoexcitations in poly(3-hexylthiophene) for the determination of the defect concentration

Abstract

Ultrafast pump-probe spectroscopy of poly(3-hexylthiophene) (P3HT) films was performed using a 9-fs laser and a broadband lock-in detection system. The fast geometrical relaxation (GR) time was attributed to the transition from a free exciton (FE) to form a bound polaron pair (BPP), and the time constant was estimated to be tau(GR) = 90 +/- 2 fs. The relaxation time constant of BPP was determined as tau(BPP) = 710 +/- 40 fs. The measurement of pump-power dependence enabled us to distinguish the defect trapping process of BPPs from other parallel decay processes and to determine the defect concentration of a P3HT thin film. (C) 2010 Elsevier B.V. All rights reserved.