Perfluorinated Anionic Surfactant Assisted Homogeneous Crystallization for Efficient and Stable Formamidinium‐Based Sn‐Pb Perovskite Solar Cells

Abstract Formamidinium (FA)‐based Sn‐Pb perovskite demonstrates superior thermal stability, making it well‐suited for all‐perovskite tandem solar cells. However, the uncontrolled crystallization process remains a significant challenge. In this study, an effective strategy is presented to regulate the crystallization of FA‐based Sn‐Pb perovskite by incorporating perfluoroanionic surfactant (perfluorohexanesulfonic acid potassium salt, F ₁₃ C ₆ SO ₃ K) into the perovskite precursor. The multifunctional sites of F ₁₃ C ₆ SO ₃ K, including F atoms and SO ₃ ⁻ groups, interact with perovskite components to stabilize the colloidal distribution of the precursor and modulate the crystallization kinetics. This results in high‐quality perovskite films with fewer defects. Consequently, the FA‐based Sn‐Pb perovskite solar cell (PSC) achieves a champion efficiency of 24.33%, with an open‐circuit voltage of 0.895 V and a fill factor of 83.2%. After continuous heating at 65 °C for 1008 h, it still maintain 91% of its initial efficiency, which shows enhanced stability. When coupled with a wide‐bandgap subcell, the all‐perovskite tandem solar cell reaches a champion power conversion efficiency (PCE) of 27.57%.