TiO₂-ZnS Cascade Electron Transport Layer for Efficient Formamidinium Tin Iodide Perovskite Solar Cells

Achieving high open-circuit voltage (V_oc) for tin-based perovskite solar cells is challenging. Here, we demonstrate that a ZnS interfacial layer can improve the V_oc and photovoltaic performance of formamidinium tin iodide (FASnI₃) perovskite solar cells. The TiO₂-ZnS electron transporting layer (ETL) with cascade conduction band structure can effectively reduce the interfacial charge recombination and facilitate electron transfer. Our best-performing FASnI₃ perovskite solar cell using the cascaded TiO₂-ZnS ETL has achieved a power conversion efficiency of 5.27%, with a higher V_oc of 0.380 V, a short-circuit current density of 23.09 mA cm^-2, and a fill factor of 60.01%. The cascade structure is further validated with a TiO₂-CdS ETL. Our results suggest a new approach for further improving the performance of tin-based perovskite solar cells with a higher V_oc.