Ytterbium Acetylacetonate as Cathode Buffer Layer for Tin‐Based Perovskite Solar Cells

ABSTRACT Tin (Sn)‐based perovskite solar cells (PSCs) are promising candidates for low‐toxicity photovoltaics. However, their performance remains limited by interfacial energy losses and cathode degradation. Here, we report a facile strategy of adopting ytterbium acetylacetonate (Yb(acac) 3 ) as a solution‐processed cathode buffer layer (CBL) to regulate the C 60 /Cu interface in Sn‐based PSCs. The introduction of Yb(acac) 3 improves energy‐level alignment, suppresses charge accumulation and recombination, and facilitates electron extraction. Meanwhile, Yb(acac) 3 forms a chemically anchored interlayer with C 60 through π – π interactions, and its hydrophobic chelate structure hinders moisture ingress and iodide‐ion migration, thereby enhancing the corrosion resistance of the Cu electrode. These interfacial effects are consistent with the strong Lewis acidity and coordination capability of Yb 3+ , which support stable interfacial binding and modified charge transport at the cathode interface. As a result, the optimized Sn‐based PSCs deliver a champion efficiency of 14.92% together with substantially improved stability, maintaining 92% of the initial efficiency after 3000 h in N 2 and ∼85% after 350 h of continuous illumination in ambient air. This work provides an acetylacetonate‐based interfacial engineering strategy for achieving high‐performance Sn‐based PSCs.