Synergistic Chemical and Field-Effect Passivation Inhibits Sn2+ Oxidation and Non-Radiative Recombination in Tin–Lead Perovskite Solar Cells

Narrow-bandgap tin–lead (Sn–Pb) perovskite solar cells (PSCs) are essential for high-performance tandem photovoltaics, yet their operational stability and efficiency suffer from spontaneous Sn2+ oxidation, interfacial defects, and non-radiative recombination. Current passivation strategies often provide only a single modification mode and struggle to adequately stabilize Sn2+ without introducing charge-transport barriers. Here, we introduce morpholine acetate (MPAC) as a novel interfacial passivator to achieve synergistic chemical and field-effect passivation in Sn–Pb perovskites. The acetate group of MPAC coordinates with undercoordinated metal cations, suppressing Sn2+ oxidation and minimizing defect states. Simultaneously, the morpholine moiety forms an interfacial dipole layer that aligns energy levels to facilitate charge extraction. Consequently, MPAC-modified PSCs achieve a champion power conversion efficiency of 22.64%. Under continuous AM 1.5G illumination without optical filters (xenon lamp, 65 °C, open-circuit conditions), the unencapsulated devices maintain over 90% of their initial efficiency after 192 h, providing a promising route to balance performance and durability.