Atomistic Insight Into Donor/Acceptor Interfaces in High-Efficiency Nonfullerene Organic Solar Cells

Donor/acceptor (D/A) interfaces play a crucial role in photoelectric conversion for organic solar cells. However, it is impossible to experimentally probe D/A interfaces at the atomistic level to date, in particular for organic solar cells based on nonfullerene acceptors due to their anisotropic structures. In this work, we have investigated the interfacial structures of a representative D-A copolymer donor PBDB-T with a well-known A-D-A structured nonfullerene acceptor ITIC, in comparison with a fullerene acceptor PC71BM, by means of atomistic simulations. It is found that owing to different side-chain steric hindrance between the polymer A and D units, both acceptors are more likely to approach the polymer A units, and more apparently for ITIC in consideration of the size and shape matching between the acceptors and the polymer A and D units. Importantly, docking of ITIC with polymer occurs mainly through local pi-pi interaction between the terminal moieties of ITIC and the A units of the polymer, and such interfacial structures are favorable for efficient exciton dissociation. Our work sheds light on the impact of side-chain nature and location as well as acceptor structures on D/A interfaces and charge-transfer dynamics, which will be very helpful for further improving the performance of organic photovoltaics.