Simply planarizing nonfused perylene diimide based acceptors toward promising non-fullerene solar cells

This work focuses on developing high-efficiency perylene diimide (PDI)-based small molecular nonfullerene acceptors with a simple synthetic strategy. We reported a new electron acceptor, Py-e-PDI, obtained via cross-coupling four PDI units with a planar pyrene core through ethynyl groups. Although the ring-fusion synthetic procedure was omitted, the large planar core and significantly reduced intramolecular steric hindrance endowed this nonfused PDI-tetramer derivative with moderate planarity. Differing from most of the PDI-tetramers with highly twisted geometries, Py-e-PDI could self-assemble into a highly ordered structure. The inverted solar cells with PTB7-Th/Py-e-PDI blends exhibited the best power conversion efficiency of up to 7.59%, which mainly resulted from the combined contribution of complementary absorption with a donor polymer, desirable aggregation and high electron mobility. Most importantly, this result demonstrates that simply planarizing 3D nonfused perylene diimide based acceptors is effective to improve the performance of the corresponding non-fullerene (NF) acceptors.