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.