PDI Derivative through Fine-Tuning the Molecular Structure for Fullerene-Free Organic Solar Cells

A perylenediimide-based (PDI-based) small molecular (SM) acceptor with both an extended π-conjugation and a three-dimensional structure concurrently is critical for achieving high-performance PDI-based fullerene-free organic solar cells (OSCs). Herein, a novel PDI-based SM acceptor has been successfully synthesized through fusing PDI units with a spiro core 4,4'-spirobi[cyclopenta[2,1-b;3,4-b']dithiophene (SCPDT) together via β-position coupling with thiophene bridges. An enhanced absorption from 350 to 520 nm has been observed. Moreover, compared with previously reported acceptor SCPDT-PDI₄, in which the PDI units and SCPDT are not fused together, the LUMO energy level of FSP (the new SCPDT-based molecule) increases. OSCs containing PTB7-Th as a donor and FSP as an acceptor have been demonstrated to show an excellent performance with a power conversion efficiency as high as 8.89%. This result might be attributed to the efficient and complementary photoabsorption, balanced carrier mobilities, and favorable phase separation in the blend film. This research could offer an effective strategy to design novel high-performance PDI-based acceptors.