Reductive Sn Compensator for Efficient and Stable Sn-Pb Mixed Perovskite Solar Cells.

Tin-lead (Sn-Pb) mixed perovskite with a narrow bandgap is an ideal candidate for single-junction solar cells approaching the Shockley-Queisser limit. However, due to the easy oxidation of Sn, the efficiency and stability of Sn-Pb mixed perovskite solar cells (PSCs) still lag far behind that of Pb-based solar cells. Herein, highly efficient and stable FAMAPbSnIBr compositional PSCs are achieved by introducing an appropriate amount of multifunctional Tin (II) oxalate (SnCO). SnCO with compensative Sn and reductive oxalate group CO effectively passivates the cation and anion defects simultaneously, thereby leading to more n-type perovskite films. Benefitting from the energy level alignment and the suppression of bulk nonradiative recombination, the Sn-Pb mixed perovskite solar cell treated with SnCO achieves a power conversion efficiency of 21.43%. More importantly, chemically reductive CO effectively suppresses the notorious oxidation of Sn, leading to significant enhancement in stability. Particularly, it dramatically improves light stability.