PDI-Based Hexapod-Shaped Nonfullerene Acceptors for the High-Performance As-Cast Organic Solar Cells

Three hexapod-shaped PDI-hexamers (PSM1, PSM2, and PSM3) with a diphenylmethylene-bridged triphenylamine (TPA) core and six peripheral PDI subunits have been designed and synthesized. The influence of different peripheral PDI subunits on the morphology and crystallinity of acceptors is investigated. Distinctly different from the previously reported PDI trimers with a TPA core, which exhibit amorphous morphologies, these hexapod-shaped acceptors display improved crystallinities and photophysical properties. Our studies have shown that PSM3 with six peripheral thiophene-fused PDI subunits gives the best result. The as-cast blend films of PBDB-T and PSM3, which possess appropriate phase separation and higher crystallinity, show high and balanced charge mobilities. As expected, OSCs with PBDB-T:PSM3 as the active layer achieve the highest power conversion efficiency of 6.71% among these three acceptors, which is the highest one in TPA-based acceptors and one of the best for the as-cast OSCs based on PDI derivatives.