Perovskite Solar Cells (PSC) research has increased noticeably in recent years as a result of significant improvements in their performance. Perovskite solar cells are a new development in Photovoltaic technology. Because PSCs are inexpensive, have the ability to tune the bandgap and are a promising future option for meeting cell efficiency limits and strong broad optical absorption. Toxicity is an important factor in the development of organic and inorganic Perovskite solar cells. PSCs based on Sn are a worthy competitor to PSCs based on Lead (Pb). The majority of them used Methylammonium tin iodide (CH3NH3SnI3) material as an absorber layer because it has greater absorption but suffers from temperature instability. As a result, in this work, we use Formamidinium tin iodide (FASnI3) absorber, which has higher temperature stability than CH3NH3SnI3Methylammonium tin iodide with a band gap of 1.4 eV. Solar cell Capacitance simulation used in this work to create FASnI3-based solar cells. This paper proposes a Power Conversion Efficiency of 24.22% for PSCs. For maximum Power Conversion Efficiency (PCE), the optimized thickness values are 10nm for CuI(Hole transport layer), 850nm for FASnI3, and 20nm for ZnOS (Electron Transport Layer). The best temperature range for device performance is around 340K. SCAPS was used to calculate the current work. In addition, we demonstrated that ZnOS is the most promising ETL as a TiO2 replacement in this work. The proposed work focuses on paving the way for novel eco-friendly non-toxic PSCs as well as investigating optimisedVoltage output circuit (Voc), Current density(Jsc), Fill factor (FF), and Power conversion Efficiency (PCE) device characteristics.