Facile synthesis of high-performance nonfullerene acceptor isomers a one stone two birds strategy

Two isomeric fused undecacyclic electron acceptors (FUIC and i -FUIC) are designed and synthesized via a one stone two birds strategy based on core unit 4TT (four thienothiophene units condensed with three cyclopentadienyl rings) and end groups 2FIC (2-(5,6-difluoro-3-oxo-2,3-dihydro-1 H -inden-1-ylidene)-malononitrile). The only difference is the two attachment positions between 4TT and 2FIC, α, α-positions for FUIC and α, β-positions for i -FUIC. FUIC exhibits stronger and red-shifted absorption with an ultra-narrow bandgap of 1.22 eV (1.28 eV for i -FUIC), a down-shifted lowest unoccupied molecular orbital energy level of −4.06 eV (−3.99 eV for i -FUIC), the same highest occupied molecular orbital energy level of −5.31 eV and a higher electron mobility of 6.8 × 10 −4 cm 2 V −1 s −1 (3.0 × 10 −4 cm 2 V −1 s −1 for i -FUIC). Organic solar cells based on a blend of PTB7-Th:FUIC exhibit a power conversion efficiency as high as 11.2% with a high fill factor of 70.6%, higher than that of PTB7-Th: i -FUIC (10.3%). Two isomeric fused undecacyclic electron acceptors (FUIC and i -FUIC) with strong near-infrared absorption are designed and synthesized via a one stone two birds strategy.