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

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.