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 Sn to oxidize into Sn 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 CsFAPbSnI 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 Sn 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 Sn 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.