Inner branched side chain tailoring on tethered small molecule acceptors for efficient polymer solar cells.

Herein, we progressively shift the branching sites of inner alkyl chains outward on the pyrrolic nitrogen atoms to obtain three tethered acceptors (TDL-C2, TDL-C3, and TDL-C4). Among them, TDL-C2 exhibits compact packing and thus favorable crystallinity, along with higher Tg, delivering a PCE of 19.02% with enhanced thermal and operational stability.