Suppressing faradaic reaction induced surface nonradiative recombination on a perovskite to improve its photovoltaic performance.

Surface nonradiative recombination in perovskites, which deteriorates the performance of perovskite solar cells (PSCs), is usually ascribed to perovskite surface defects and interface energy level mismatch. In this study, by combining in situ X-ray photoelectron spectroscopy (XPS), electrochemical methods and photoluminescence (PL) spectroscopy, we find that surface nonradiative recombination is induced by faradaic reactions between Pb2+/Pb2-x and I-/I-1+x on the FAPbI3 surface under illumination. Depositing Tm(NO3)3 on the FAPbI3 surface suppresses the Pb2+ + xe- ↔ Pb2-x faradaic reaction, thereby decreasing the surface nonradiative recombination and boosting the power conversion efficiency of an FAPbI3 solar cell from 20.29% to 23.15%. The finding offers new understanding of surface nonradiative recombination in perovskites, which is helpful for designing and constructing high-performance perovskite photovoltaics.