Stable tin–lead perovskite inks for efficient all-perovskite tandems

Low-bandgap ( E g  ~ 1.25 eV) tin–lead perovskite solar cells hold great potential for constructing efficient all-perovskite tandem solar cells (TSCs). However, rapid degradation of perovskite precursor solutions, owing to easy oxidation of Sn 2+ , remains a major challenge. Here we elucidate oxidation pathways in Sn–Pb perovskite precursors. We further introduce basic amino acids and basic amino acids sulfate (BAAS) as proton scavengers, which stabilize the ink for over 300 days. BAAS neutralizes excess protons to mitigate dimethyl sulfoxide-driven oxidation reactions, whereas sulfate ions coordinate Sn 2+ to passivate defects and regulate crystallization. The optimized low-bandgap perovskite solar cell achieves a power conversion efficiency of 24.06% with an open-circuit voltage of 0.905 V, enabling two-terminal all-perovskite TSCs with a power conversion efficiency of 30.24% (certified 29.56%). The BAAS-passivated TSCs retain over 85% of their initial performance after 1,000 hours of the maximum power point operation under 1-sun illumination.