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In this work, a star-shaped planar acceptor named FTr-3PDI was synthesized via ring-fusion between truxene core and three bay-linked perylene diimide (PDI) branches. Compared to the unfused non-planar acceptor Tr-3PDI, FTr-3PDI exhibits better structural rigidity and planarity, as well as more effective conjugation between truxene core and PDI branches. As a result, FTr-3PDI shows up-shifted energy levels, enhanced light absorption coefficient, increased electron mobility, and more favorable phase separation morphology in bulk-heterojunction (BHJ) blend films as compared to Tr-3PDI. Consequently, FTr-3PDI afforded higher power conversion efficiency (PCE) in BHJ solar cells when blended with a polymer donor PTB7-Th. This work demonstrates that ring-fusion is a promising molecular design strategy to combine the merits of truxene and PDI for non-fullerene acceptors used in organic solar cells.

Two new star‐shaped and fused electron acceptors, TITT‐3IC and TITT‐3ICF have been designed and synthesized, which consist of a C3h‐symmetric coplanar trindeno[1, 2‐b: 4, 5‐b′: 7, 8‐b′′]trithiophene (TITT) as the central core and 3‐(dicyanomethylidene)indan‐1‐one and 2‐(5,6‐difluoro‐3‐oxo‐2,3‐dihydro‐1H‐inden‐1‐ylidene) malononitrile as the peripheral electron‐withdrawing groups, respectively. With the large coplanar configuration and electron‐rich nature of π‐conjugated backbone, these two acceptors exhibit strong intermolecular charge transfer absorption in the region of 500–650 nm with the optical band gaps around 1.9 eV. Relative to TITT‐3IC, TITT‐3ICF shows the downshifted LUMO level and the slightly redshifted absorption with the higher molar extinction coefficient due to the stronger electron‐withdrawing effect of fluorination. When blending with PTB7‐Th, the TITT‐3ICF‐based device displays a higher power conversion efficiency (PCE) of 4.26 % than the TITT‐3IC‐based device (PCE=3.87 %). Comparing with the TITT‐3IC‐based device, the increased short circuit current (JSC) and fill factor (FF) are responsible for the higher PCE value of the TITT‐3ICF‐based device, which benefits from its strong and redshifted absorption for light harvesting and proper phase separation morphology for effective exciton dissociation and charge transport. This work demonstrates that as an alternative electron‐donating core, TITT will be promising in designing star‐shaped non‐fullerene materials. Fusing stars: C3h‐symmetric coplanar trindeno[1, 2‐b: 4, 5‐b′: 7, 8‐b′′]trithiophene has been employed as the central core to construct star‐shaped fused‐ring electron acceptors, TITT‐3IC and TITT‐3ICF, achieving the maximum PCE of 3.87 and 4.26 %, respectively. [ABSTRACT FROM AUTHOR]