The effects of the side-chain length of non-fullerene acceptors on their performance in all-small-molecule organic solar cells

A series of acceptor-donor-acceptor type non-fullerene acceptors (NFAs), FCn-2Cl, with gradient substitution lengths of side chains (SCs) on molecular backbones, have been designed and synthesized for all-small-molecule organic solar cells (ASM-OSCs). The effects of SC length ranging from n-butyl to n-dodecyl on their optoelectronic properties, molecular packing, blend film morphology and overall photovoltaic performance have been systematically studied. Our results show that the BSFTR:FC10-2Cl-based ASM-OSC exhibited the best power conversion efficiency of over 12% due to its more efficient exciton dissociation, less charge recombination, balanced charge mobility and favorable morphology. Our work highlights the importance of fine-tuning the length of SCs of NFAs for further improving the performance of ASM-OSCs.