Antisolvent‐Free Dual‐Anion Regulation for High‐Efficient Sn‐Pb and All‐perovskite Tandem Solar Cells

Mixed tin-lead (Sn-Pb) perovskites are integral to all-perovskite tandem solar cells (TSCs), offering significant potential to surpass the theoretical efficiency limits of single-junction solar cells. However, the rapid crystallization of Sn-Pb perovskite thin films and the propensity of Sn²⁺ to oxidize into Sn⁴⁺ remain critical challenges, hindering device performance and stability. Herein, it is demonstrated that a multifunctional dual-anion synergistic regulation strategy to fabricate high-quality MA-free Cs_0.1FA_0.9Pb_0.5Sn_0.5I₃ perovskite thin films with superior morphology and crystallinity via a simplified antisolvent-free spin-coating process. Acetate anions (Ac^-) derived from formamidinium acetate (FAAc) effectively regulate crystallization kinetics and mitigate Sn²⁺ oxidation via intermediate phase formation and anion exchange process. Simultaneously, the combination of Ac^- and thiocyanate anions (SCN^-) from guanidinium thiocyanate (GuaSCN) promotes larger crystal grain growth and stabilizes Sn²⁺ via strong coordination interactions. The dual-anion strategy effectively minimizes grain boundaries, suppresses non-radiative recombination, and optimizes the energy level alignment at interfaces. As a result, the champion single-junction Sn-Pb perovskite solar cell (PSC) achieves an impressive power conversion efficiency (PCE) of 23.26%, setting a new benchmark for Sn-Pb PSCs fabricated without antisolvent. While all-perovskite TSCs reach 28.07% efficiency with remarkable operational stability, retaining 81% of initial performance after 600 h under maximum power point tracking.