Abstract
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(2+), 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 FA(0.5)MA(0.5)Pb(0.5)Sn(0.5)I(0.47)Br(0.03) compositional PSCs are achieved by introducing an appropriate amount of multifunctional Tin (II) oxalate (SnC(2)O(4)). SnC(2)O(4) with compensative Sn(2+) and reductive oxalate group C(2)O(4) (2-) 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 SnC(2)O(4) achieves a power conversion efficiency of 21.43%. More importantly, chemically reductive C(2)O(4) (2-) effectively suppresses the notorious oxidation of Sn(2+), leading to significant enhancement in stability. Particularly, it dramatically improves light stability.