A Noncovalently Fused‐Ring Asymmetric Electron Acceptor Enables Efficient Organic Solar Cells

Main observation and conclusion Recently, the asymmetric nonfullerene acceptors (NFAs) with acceptor‐donor‐acceptor (A‐D‐A) structure have been developed rapidly, especially for the modification of asymmetric core, asymmetric side chains and asymmetric end groups. In this work, a novel asymmetric A‐D‐π‐A type NFA with a noncovalently fused‐ring core named PIST‐4F is synthesized, containing an indacenodithieno[3,2‐b]dithiophene (IDT), two strong electron‐withdrawing end groups and an alkylthio‐substituted thiophene π‐bridge. Benefiting from the S···S noncovalent interaction between the sulfur atom on π‐bridge and the adjacent thiophene in IDT, the PIST‐4F presents nearly planar geometry and extended conjugated area, resulting in the optimized electronic properties, charge transport, and film morphology compared to the symmetric NFA PI‐4F. As a result, PM6:PIST‐4F‐based devices achieve a higher power conversion efficiency (PCE) of 13.8%, while the PM6:PI‐4F‐based devices only show a PCE of 7.1%. Notably, the PM6:PIST‐4F‐based devices processed with nonhalogen solvent toluene exhibit an excellent PCE as high as 13.1%. These results indicate that PIST‐4F is an effective acceptor for high‐efficiency organic solar cells.