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-pi-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 pi-bridge. Benefiting from the S center dot center dot center dot S noncovalent interaction between the sulfur atom on pi-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. [GRAPHICS] .