Efficient Small-Molecule Organic Solar Cells by Modulating Fluorine Substitution Position of Donor Material

The fluorine substitution position in organic semiconductors is critical in improving device performance for organic solar cells (OSCs). Herein, two similar small-molecule donors, B3T-PoF and B3T-PmF, are designed and synthesized, which only differ on the fluorine substitution position on the pendent benzene unit. Although both small-molecule donors exhibit similar absorption profiles and molecular energy levels, B3T-PmF has stronger crystallinity and lower energetic disorder than B3T-PoF. After blending with the non-fullerene acceptor of BO-4Cl, B3T-PmF shows better phase separation and more ordered molecular packing in blend film. As a result, the B3T-PoF:BO-4Cl-based OSC shows a power conversion efficiency (PCE) of 12.3%. In contrast, the B3T-PmF:BO-4Cl-based cell demonstrates obviously increased J(SC) and FF values, thus yielding an excellent PCE of 14.7%. This study indicates that reasonable selection of fluorine atom substitution position in conjugated side chains is one of the promising strategies for achieving high-performance SM-OSCs.