Pioneering Interface Configuration with Fermi‐Level Tailoring for Tin Perovskite Photovoltaics

Abstract Tin‐based perovskite solar cells (TPSCs) have attracted attention for their environmentally friendly and high theoretical efficiency. However, their current efficiency remains substantially lower than that of lead‐based devices, which due to nonideal film quality and interfacial energy level mismatch. In the inverted structure, conventional hole transport materials, PEDOT:PSS, exhibits nonideal energy level alignment with perovskite, leading to carrier accumulation and recombination. Here, we designed and synthesized a carbazole‐based phosphonic acid self‐assembled monolayer with terminal methylthio groups, which was introduced beneath PEDOT:PSS to construct a composite hole transport layer structure. This architecture, enabled by methylthio groups linkages that ensured intimate interfacial contact and improved energy‐level alignment, effectively suppressed recombination losses and facilitated more efficient hole extraction. Consequently, the optimized device achieved an impressive power conversion efficiency of 15.11% along with excellent operational stability under various conditions. This work provides new insights into interfacial fermi‐level tailoring, paving the way for high‐performance TPSCs.