Fullerene Derivative-Modified SnO2 Electron Transport Layer for Highly Efficient Perovskite Solar Cells with Efficiency over 21%

Tin dioxide (SnO2) has been widely applied as an electron transport layer (ETL) for the n-i-p-type perovskite solar cells (Pero-SCs). However, the existence of defects at the surface of SnO2 and the hysteresis behavior of the devices with SnO2 ETL limit its application in the Pero-SCs. In this study, a fullerene derivative pyrrolidinofullerene C60-substituted phenol (NPC60-OH) was synthesized and applied to modify the SnO2 ETL in Pero-SCs for the first time. The systematic and comparative characterizations demonstrated that, after the introduction of an NPC60-OH modification layer on the SnO2 ETL, the perovskite films in the corresponding device showed enlarged grain size and these devices presented enhanced electron transport and decreased charge recombination velocity. Besides, the NPC60-OH layer could significantly reduce the trap-state density in the perovskite film. As a result, a champion power conversion efficiency (PCE) of 21.39% was achieved for the SnO2/NPC60-OH-based Pero-SCs, with suppressed hysteresis and improved stability, while the control devices with pristine SnO2 ETL showed a lower PCE of 19.04%.