Estimating donor:acceptor compatibility for polymer solar cells through nonfused-ring acceptors with benzoxadiazole core and different halogenated terminal groups

Benzoxadiazole derivatives have been rarely employed in designing non-fused ring electron acceptors (NFREAs). Herein, two novel NFREAs consisting of uniform difluorobenzoxadiazole cores, cyclopentadithiophene bridges, and different fluorinated/chlorinated dicyanoindanone end-groups were developed and named as BOCIC-4F and BOCIC-4Cl, respectively. Apart from the differences in physical properties, different halogenations on NFREAs simultaneously lead to variations in compatibility with different polymer donors. In succession, the polymer donors, PBDB-T and PBDB-TF, were employed to form different donor:acceptor pairs with two NFREAs to estimate the compatibility in varied blends. Polymer solar cells (PSCs) based on fluorinated BOCIC-4F yielded the best photovoltaic performance with nonhalogenated PBDB-T. However, the efficiency diminished when PBDB-T was changed to halogenated PBDB-TF. In contrast, the chlorinated BOCIC-4Cl, which achieved the poorest performance with PBDB-T, could work better with PBDB-TF. Disparities in aggregation behaviors, miscibility factors, blend morphologies, and carrier dynamics derived from the different halogenations on NFREAs were responsible for the contrary compatibility in different blends. This work demonstrates the potential of benzoxadiazole derivatives in the design of efficient NFREAs. Moreover, these results will also be useful for constructing high-performance PSCs by estimating the compatibility of various donor:acceptor pairs.