Interfacial and Thickness Engineering Enabling 19.67% Efficient Lead‐Free FASnI ₃ Perovskite Solar Cells

Perovskite solar cells established with tin‐ and lead‐free active materials offer high‐efficiency, low‐cost, and nontoxic technology for future energy applications. However, tin‐based perovskites, such as FASnI 3 , still face challenges, including charge recombination and poor energy‐level alignment with adjacent transport layers, which limit device performance. Optimizing the cell layers to perform their functions is essential for improving overall performance. In this work, we tackled those limits through targeted material and interfacial engineering. We inserted the organic semiconductor C 46 H 46 N 2 (TAPC) as a hole transport/electron blocking layer to improve the alignment of energy levels at the anode interface and suppress recombination, and we added an ultrathin NiO buffer to optimize charge extraction and enhance film quality. Furthermore, we precisely tuned the total film stack thickness to strike the best balance between lateral conductivity and leakage suppression, avoiding shunts while preserving efficient carrier transport. To further improve performance, different transparent conductive oxides were investigated as the top electrode to achieve optimal light transmission and efficient carrier transport. After optimization, the final FASnI 3 device delivered a stabilized power conversion efficiency of 19.67%.