Regulating Surface Heterogeneity Maximizes Photovoltage and Operational Stability in Tin–Lead Perovskite Solar Cells

We present a surface reconstruction strategy for tin–lead perovskites, effectively addressing the issue of oxidized Sn fragments on surfaces and interfaces. Our surface treatment involving postfabrication iodide supplementation effectively regulates undesired surface binding states and reconstructs the compositional gradient. Through surface-sensitive and depth-resolved analysis, we unveil a strong correlation among surface compositional disorder, photovoltage, and operational stability in tin–lead perovskites. Surface-reconstructed perovskite films demonstrate improved carrier lifetime, reduced defect density, and higher recombination resistance compared with untreated films. As a result, devices utilizing surface-reconstructed perovskites exhibit remarkable performance with high power conversion efficiency (up to 23%) and open-circuit voltage (0.88 V), alongside enhanced operational stability compared to untreated counterparts. These insights into the surface vulnerabilities of mixed tin–lead perovskites, coupled with the underlying chemistry of surface passivation, pave the way for significant advancements in narrow-band gap perovskite solar cells.