Charge Carrier Dynamics in Bulk Heterojunction Organic Semiconductor by Optical-Pump Terahertz-Probe Spectroscopy

We use optical-pump terahertz (THz)-probe spectroscopy to investigate charge carrier dynamics in bulk heterojunction (BHJ) organic semiconductor thin films based on diketopyrrolopyrrole-linked tetrabenzoporphyrin and fullerene derivative (PCBM). Transient THz signals decay with time constants of 0.7 ps and 18 ps. Compared with BP:PCBM thin film, we find that mobile charge carriers survive on a longer time scale. Furthermore, the amplitude of the fast decay components depends on the excitation fluence, which is due to charge pair annihilation at the higher carrier density.