Alkyl Branching Sites on π-Spacers for Dipyran-Based High-Efficiency Organic Solar Cells

The configuration of A-π-D-π-A type is one effective way for nonfullerene acceptor (NFA) design to achieve excellent photovoltaic performance with reduced synthetic complexity. Additional side chain engineering either around the center or at the terminus of the D core has been widely adopted in the molecular optimization of A-D-A type NFAs. Herein, the branch alkyl and branched sites of the side chains on π-spacers of A-π-D-π-A type acceptors are carefully evaluated, where dipyran ladder-type core Ph -DTDP i is employed as the D core. All three dipyran-based acceptors have been fully characterized and distinct behaviors have been detected in solid UV–vis absorption spectra, molecular stacking orientation, and miscibility with the polymer donor accompany with the side chain alternation. The balanced crystallization characteristics and good miscibility endows the blend film of DTDP i -C2:PBDB-T with a uniform morphology containing even smaller nanoscopic structures with interweaved fibers and balls, which enlarges the donor–acceptor contact and facilitates efficient exciton diffusion and separation. Hence, Ph -DTDP i -C2 -based devices achieved a high PCE of 12.4% with a high J SC of 21.88 mA/cm 2 and significantly enhanced FF of 69.26%. In short, adjusting the alkyl branch point on the π bridge is an effective strategy for dipyran-based acceptor and future molecular design.