A simple method to experimentally determine the accurate RC-constant in nanosecond timescale transient photocurrent measurements on organic solar cells

Abstract

Nanosecond timescale transient photocurrent (ns-TPC) measurements on organic solar cells (OSCs) are commonly used in combination with numerical simulation to study charge transport and recombination phenomenon in these devices. But the ns-TPC measurement itself is influenced by the RC-effects of the test circuit. Thus the RC-constant of the test circuit is needed to mathematically eliminate the RC-effects to reconstruct an accurate TPC signal. Nowadays, an estimated RC-constant is used by researchers to reconstruct the TPC signal. So, a reliable method is needed to experimentally determine the RC-constant accurately to reconstruct the accurate TPC signal. Here, a simple method, by analyzing the transient response of the test circuit after a square voltage pulse excitation, is used to experimentally determine the RC-constant in ns-TPC measurements on typical planar hetero-junction small-molecule organic solar cells and typical bulk hetero-junction polymer solar cells. In the meantime, in order to verify the correctness of the experimentally determined RC-constant, three verification methods, which are valid under specific conditions, are selectively adopted to verify whether the experimentally determined RC-constant is reliable. Finally, all the results given by the verification methods show that this simple method could be used as a reliable method to experimentally determine the correct RC-constant in ns-TPC measurements on OSCs.