Photoinduced intra- and inter-molecular charge transfer dynamics in organic small molecules with an intra-molecular push–pull electronic structure

Abstract

As electron acceptor materials, organic small molecules with an intra-molecular push–pull electronic structure have been widely used in high-efficient organic solar cells (OSCs), usually referred to as non-fullerene acceptor (NFA) molecules. Compared with fullerene acceptor molecules, an interesting discovery is that these molecules behave in both photoinduced intra- and inter-molecular charge transfer (CT) effects, thus resulting in some unique photophysical processes and phenomena during the operation of OSCs. In this study, by separately applying a photoexcitation to a single NFA molecule and different molecular aggregates, we clarify the photoinduced electron transition details (including transition mode, peak position, and probability), the resulting intra- and inter-CT dynamics, and the modulating methods (such as the intra-molecular electronic push–pull potential, the inter-molecular aggregation mode, and the photoexcitation intensity). Clarifications of these microscopic quantum processes should be helpful to further understand the photoinduced experimental observations in NFA molecules, and thus provide a clear direction for their rational design to improve the photoinduced charge yield in their aggregates.