Multiple active site additive-mediated suppression of Sn²⁺ oxidation and regulation of crystallization for high-performance Sn–Pb mixed perovskite solar cells

The oxidation of Sn²⁺ and fast crystallization jointly limit the photovoltaic performances and stability of tin (Sn)-lead (Pb) mixed perovskite solar cells, but the mitigation of a single issue only obtains restricted enhancement of device performance. Herein, we introduce <i>N</i>-hydroxythiophene-2-carboximidamide (NHC) as a multiple active site additive, the rich functional groups of which can interact with perovskite to form strong Lewis acid-base coordination and abundant hydrogen bonds, simultaneously suppressing Sn²⁺ oxidation and regulating crystallization rate. The NHC-treated Sn-Pb mixed perovskite exhibited lower defect density, reduced non-radiative recombination, and improved carrier transport dynamics. As a result, the optimized device showed superior champion efficiency of 23.49% with a high open-circuit voltage of 0.882 V, as well as outstanding stability, maintaining 89% of its original value after 880 hours of continuous one-sun illumination.