Non-fullerene small molecule acceptors with three-dimensional thiophene/selenophene-annulated perylene diimides for efficient organic solar cells

New three-dimensional non-fullerene small molecule acceptors were synthesized with the structure of a spiro core, 4,4'-spirobi[cyclopenta[2,1-b;3,4-b']dithiophene] (SCPDT) linked with S/Se fused perylene diimides (PDIs). The three-dimensional structure suppresses the aggregation of PDIs and the formation of excessively large crystalline domains. The well-conjugated structure and electron-rich property of the spiro core give rise to high electron mobility, making for more balanced carrier transport. The introduction of S/Se aromatic rings leads to appropriate energy levels and more twisted molecular configurations. Organic solar cells based on the PBDB-T-S:SCPDT-PDI₄-S bulk heterojunction exhibit a high power conversion efficiency of 6.95% along with a highV_ocof 1.00 V, aJ_scof 11.72 mA cm^-2and a fill factor of 59.27%.