TiO 2 -ZnS Cascade Electron Transport Layer for Efficient Formamidinium Tin Iodide Perovskite Solar Cells.

Achieving high open-circuit voltage (Voc ) for tin-based perovskite solar cells is challenging. Here, we demonstrate that a ZnS interfacial layer can improve the Voc 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 Voc 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 Voc .