Abstract

Open-circuit photovoltage decay from the steady state for the determination of bimolecular recombination constants has been studied in organic solar cells (OSCs) with three prototypical bulk heterojunctions including fullerene and non-fullerene acceptors. A simple theory for the determination of recombination constants from the initial decay rate of the open-circuit photovoltage was shown. The effective lifetimes were experimentally determined from the initial decay rates and were proportional to the −0.5 power of the excitation light intensity, indicating that the recombination process under the open-circuit condition in the OSCs is bimolecular. The experimental setup was also simple, and hence the experiment and the analysis are applicable to a variety of OSCs under operation. Information on the transport properties including bimolecular recombination constants is useful for the design and the optimization of the device architecture of OSCs.