Side‐chain engineering of benzimidazole‐incorporated A‐<scp>DA</scp>'D‐A type acceptors for organic solar cells and field‐effect transistors

Abstract A series of A‐DA'D‐A type non‐fullerene acceptors (NFAs) using benzimidazole (BIm) as the central acceptor (A') were developed. Side‐chain engineering at the carbon‐2 (C2) position (hydrogen or methyl or ethylhexyl) of the central imidazole moiety leads to the formation of three I‐series NFAs, IM‐H, IM‐M, and IM‐EH, respectively. The PM6:IM‐M bulk heterojunction (BHJ) device demonstrated the highest power conversion efficiency (PCE) of 10.09% due to its better miscibility with the PM6 polymer. Furthermore, the planar‐mixed heterojunction (PMHJ) devices of PM6/IM‐M further improved the PCE to 12.68%. The observed enhancement can be attributed to the efficient charge transfer and the mitigation of recombination processes. Meanwhile, IM‐M exhibited ambipolar charge transport behavior in organic field‐effect transistor (OFET) devices, with balanced electron and hole mobilities of 0.028 and 0.024 cm 2 V −1 s −1 , respectively.