Multiple-Time Scale Exciton Dynamics in Organic Photovoltaic Devices.

Organic photovoltaics (OPVs) are regarded as one of the most promising candidates for various outdoor and indoor application scenarios. The development and application of nonfullerene acceptors have pushed power conversion efficiencies (PCEs) of single-junction cells to exceed 19%, and values approaching 20% are within sight. This progress has resulted in some unexpected photophysical observations deserving more in-depth spectroscopic research. In this Perspective, we have summarized recent photophysical advances in accordance with results of ultrafast spectroscopy in our and other groups and provide our point of view on multiple-time scale exciton dynamics involving the following aspects: long-range exciton diffusion driven by dual Förster resonance energy transfer, origins of driving force for hole transfer under small energy offsets, trap-induced charge recombination in outdoor and indoor OPVs, and a picture of real-time evolution of excitons and charge carriers regarding stability. Moreover, our understanding of the photophysical property-function relationship is proposed in state-of-the-art OPVs. Finally, we point out the remaining challenges devoted to the further development of versatile OPVs.