Aggregation effect of acceptor molecules on the energy and charge transfer dynamics at an organic donor/acceptor interface

The synergy and competition between energy and charge transfer at organic donor/acceptor (D/A) interfaces have been confirmed to remarkably impact the interfacial photovoltaic processes of organic solar cells (OSCs). In this work, we theoretically clarify the aggregation effect of acceptor molecules on the energy/charge transfer dynamics, and present their quantitative correlations. The D/A interface is constructed by employing an extended Su-Schrieffer-Heeger tight-binding model, where the interfacial electronic structure is modulated by tuning the on-site energy of donor molecule. As a general result, for both type-I and type-II electronic structures, the aggregation of acceptor molecules always favors the energy transfer, while suppressing the charge transfer. It means that, by strengthening the aggregation of acceptor molecules, we can effectively convert donor excitation into acceptor excitation, which thus provides a direction for fully utilizing the acceptor excitation to reduce the voltage loss in OSCs.