Surface Sn(IV) Hydrolysis Improves Inorganic Sn-Pb Perovskite Solar Cells

Cesium tin–lead (Sn–Pb) perovskites are exceptional for their combined capabilities in unlocking ideal bandgaps for solar cells and mitigating the stability issue faced by their hybrid organic–inorganic counterparts. But the development of high-performance solar cells using these materials is retarded by their inherent high density of detrimental Sn(IV) defects. Herein, we demonstrate a sequential surface treatment method, which entails a Sn(II) halide treatment to displace the buried Sn(IV) ions underneath the film surface, followed by a H₂O treatment to hydrolyze the displaced Sn(IV) ions. The surface treatment induces chemical and microstructural reconstructions that significantly improve the optoelectronic properties and stability of perovskites. As a result, a power conversion efficiency of 16.79% and a T₉₀ stability of 958 h are achieved, topping all previously reported performance parameters for inorganic Sn–Pb PSCs. This achievement further shortens the performance gap between all-inorganic and hybrid organic–inorganic Sn–Pb PSCs with sub-1.4 eV bandgaps.