Efficient and Stable Surface Passivation of Tin–Lead Perovskite Using Basicity Weakened Oxamide

Tin–lead (Sn–Pb) perovskites, owing to their ideal optical bandgap, have emerged as the preferred material for constructing high-efficiency, low-cost perovskite tandem solar cells (TSCs). Organic amines like ethylenediamine (EDA) have been demonstrated as efficient surface passivation agents for Sn–Pb perovskite due to their ability to chelate tin atoms and selectively remove excess tin from the surface. However, their strong basicity can cause irreversible damage to the surface of Sn–Pb perovskite, compromising interfacial stability and even the long-term device stability. To overcome this limitation, this study introduces basicity weakened oxamide (OAM) as an alternative to EDA for Sn–Pb perovskite surface passivation. Compared to EDA-treated films, the OAM-passivated Sn–Pb perovskite films exhibit a higher photoluminescence quantum yield and superior thermal stability, even under harsh aging conditions of 85 °C for 5 days. The champion power conversion efficiency (PCE) was increased from 21.43 to 22.50%, and the OAM-based devices retained 83.35% of their initial PCE after 707 h operation, far surpassing the EDA-treated devices (80% retention after 147 h). When this approach was extended to TSCs, a PCE of 28.10% was achieved alongside a substantial enhancement in operational stability, with the T 90 lifetime (the time to retain 90% of the initial PCE) increasing from 161 to 670 h.