Core-expanded naphthalenediimide derivatives as non-fullerene electron transport materials for inverted perovskite solar cells

Two core-expanded naphthalenediimide (NDI) derivatives NDI3HU-DTYM2 (1) and (DTYM-NDI-DTYA)(2) (2) with coplanar and twisted molecular backbones, respectively, were used as low-temperature solution-processed electron transport materials (ETMs) for CH3NH3PbI3-based inverted planar perovskite solar cells (PSCs). The high electron mobility as well as low-lying lowest unoccupied molecular orbital (LUMO) energy levels and good film-formation ability on perovskite layers make 1 and 2 both promising ETMs for PSCs. The PSCs devices based on 1 show a power conversion efficiency (PCE) of 8.7%, while the PSCs devices based on 2 that has twisted molecular backbone exhibit a PCE value of up to 12.9%, a short-circuit current density (J(sc)) value of 22.80 mA cm(-2) with negligible hysteresis, which is comparable to that of PCBM-based PSCs devices. Our results demonstrate that core-expanded NDI-based n-type organic semiconductors, especially those with twisted molecular backbones, have great potential for high-performance, low-cost, solution-processed non-fullerene ETMs in PSCs.