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%.