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 T₉₀ lifetime (the time to retain 90% of the initial PCE) increasing from 161 to 670 h.