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

Abstract

We investigated charge-carrier dynamics in benzoporphyrin (BP) and BP-based bulk heterojunction (BHJ) films with optical pump-broadband terahertz (THz) probe spectroscopy. In both samples, we observed instantaneous appearance of transient THz signals, which are attributed to mobile charge carriers that are much lower in transition energy than excitons. These carriers recombine and/or trap at defect sites within a few ps. In the BP-based BHJ films, the decay dynamics of transient THz signals was faster relative to that in the BP films. In contrast to the BP films, approximately 10% of the transient signal does not decay within 35 ps, indicating survival of free charge carriers.