Numerical Simulation and Optimization of Highly Stable and Efficient Lead-Free Perovskite FA 1-x Cs x SnI 3 -Based Solar Cells Using SCAPS.

Formamidinium tin iodide (FASnI 3 )-based perovskite solar cells (PSCs) have achieved significant progress in the past several years. However, these devices still suffer from low power conversion efficiency (PCE=6%) and poor stability. Recently, Cesium (Cs)-doped Formamidinium tin iodide (FA1-xCsxSnI3) showed enhanced air, thermal, and illumination stability of PSCs. Hence, in this work, FA1-xCsxSnI3 PSCs have been rigorously studied and compared to pure FASnI 3 PSCs using a solar cell capacitance simulator (SCAPS) for the first time. The aim was to replace the conventional electron transport layer (ETL) TiO 2 that reduces PSC stability under solar irradiation. Therefore, FA1-xCsxSnI3 PSCs with different Cs contents were analyzed with TiO 2 and stable ZnOS as the ETLs. Perovskite light absorber parameters including Cs content, defect density, doping concentration and thickness, and the defect density at the interface were tuned to optimize the photovoltaic performance of the PSCs. The simulation results showed that the device efficiency was strongly governed by the ETL material, Cs content in the perovskite and its defect density. All the simulated devices with ZnOS ETL exhibited PCEs exceeding 20% when the defect density of the absorber layer was below 1015 cm-3, and deteriorated drastically at higher values. The optimized structure with FA75Cs25SnI3 as light absorber and ZnOS as ETL showed the highest PCE of 22% with an open circuit voltage Voc of 0.89 V, short-circuit current density Jsc of 31.4 mA·cm-2, and fill factor FF of 78.7%. Our results obtained from the first numerical simulation on Cs-doped FASnI 3 could greatly increase its potential for practical production.