Continuous-wave photoinduced absorption studies in polythiophene and fullerene blended thin films

摘要

The generation and recombination dynamics of photocarriers (polarons) in poly(3-hexylthiophene) and [6,6]-phenyl-C_(61)-butyric acid methyl ester blended thin films have been investigated by means of continuous-wave photoinduced absorption spectroscopy. Continuous-wave photoinduced absorption spectroscopy has the advantage of being used to investigate long-lived excited species with lifetimes that range from microseconds to milliseconds. In this time range, three kinds of excited species are recognized in the blends: trapped, mobile, and delocalized polarons. From the modulation-frequency dependence, the mean lifetimes of the three types of polarons at low temperature were estimated. It is known that polarons are not generated directly by the pump beam but rather through Coulombically bound radical pairs. We have found that this two-step model for polaron generation can be recognized on a microsecond time scale by continuous-wave photoinduced absorption measurements.