The effects of electronic structures of two non-fullerene systems on their photovoltaic performances.

In this contribution, the electronic structures of two polymer donors (PBDB-T and PBDB-T-SF) and two non-fullerene acceptors (ITIC and IT-4F) are researched by density functional theory and time-dependent density functional theory, respectively. The research purpose is to rationalize the relationship between observed experimental performances and structural properties and obtain the effects of structures on their photovoltaic performances. The investigated properties involve in the structure characteristics, absorption spectra, carrier mobilities, and exciton dissociation properties at interfaces to locate the essences of different power conversion efficiency between PBDB-T/ITIC and PBDB-T-SF/IT-4F. The results suggest that both PBDB-T/ITIC and PBDB-T-SF/IT-4F systems have stable structures and relatively high HOMO levels, which benefits to relatively large V values. In addition, the larger PCE of PBDB-T-SF/IT-4F system originates from PBDB-T-SF's large hole transport properties and better exciton dissociation ability. Furthermore, the F and S incorporations enhance hole mobilities and exciton dissociation ability. Consequently, the theoretical results coincide well with the experimental ones.