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

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, F13C6SO3K) into the perovskite precursor. The multifunctional sites of F13C6SO3K, including F atoms and SO3- 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 degrees 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%.