A Multifunctional Reducing Molecular Dopant for 16% Efficient Tin Perovskite Solar Cells

Although lead‐based photovoltaics have seen remarkable progress, tin‐based perovskite solar cells (Sn‐PSCs) continue to face challenges due to their limited power conversion efficiency and insufficient operational stability. The primary cause of this performance gap is the susceptibility of Sn 2+ to oxidation, which promotes rapid defect formation within the material. To address these issues, we introduced a multifunctional reducing agent—6‐(TrifluoroMethyl)benzo[b]thiophen‐3(2H)‐one 1,1‐Dioxide (CF3BTD)—into the FASnI 3 absorber layer. This molecular additive serves a dual purpose: it effectively suppresses the oxidation of Sn 2+ ions while simultaneously passivating bulk defects. As a result, the treated films exhibit improved carrier dynamics and enhanced crystallinity. Devices optimized with CF3BTD achieved a champion power conversion efficiency of 16.00%, with a certified efficiency of 15.06%, ranking them among the highest‐performing Sn‐PSCs reported to date. Furthermore, these unencapsulated devices demonstrated exceptional operational stability, retaining over 90% of their initial performance after 600 h under continuous white LED illumination at 100 mW cm −2 with maximum power point tracking in a nitrogen atmosphere. This work represents a significant step forward in the development of efficient and stable lead‐free perovskite photovoltaics.