Charge carrier dynamics in benzoporphyrin thin films investigated by time-resolved THz spectroscopy

We performed optical pump-terahertz (THz) probe measurements to investigate the charge carrier dynamics of benzoporphyrin (BP) and BP-based bulk heterojunction (BHJ) thin films. In both samples, we observed an instantaneous appearance of transient THz signals which are attributed to polaron pairs. These polaron pairs recombine and/or trap in a defect site to localize within 1 ps time scale. From analysis of the transient complex conductivity spectra, we found that the conductivity spectra can be well reproduced by Drude-Smith model. For BP-based BHJ films, a faster decay dynamics of the transient THz signals was observed compared to BP films.