Picosecond time-resolved infrared absorption study on photoexcited dynamics of regioregular poly(3-hexylthiophene)

Picosecond time-resolved infrared absorption spectra of the photoexcited states of a spin-coated film of regioregular poly(3-hexylthiophene) (RR-P3HT) have been recorded at 77 K. The time-resolved photoinduced infrared absorptions due to electronic transitions at 2500 cm−1 and vibrational transitions at 1575 cm−1 have fast and slow decay components. By comparing the picosecond time-resolved infrared absorption spectrum of long-lived (slow decay component) transient species with the doping-induced infrared difference spectrum of RR-P3HT, the long-lived transient species are assigned to polarons. The short-lived transient species are assigned to singlet excitons and/or polaron pairs.