This research paper focuses on the design and optimization of solar cell (photovoltaic cell) based on FASnI3 perovskite with PEDOT-WO3 serving as the hole transport layer (HTL) and PCBM serving as the electron transport layer (ETL). The study aims to analyze the impact of interface defect densities (IDD) at the FASnI3/HTL and FASnI3/ETL interfaces on the performance of the photovoltaic cell. This research investigates the role of HTL and ETL in reducing IDD and improving the efficiency of solar cells. The paper discusses the importance of perovskite solar cells (PSCs), their basic structure, and their operation. The research paper highlights PSCs’ high efficiency and low-cost fabrication potential. FASnI3 perovskite has emerged as a promising candidate due to its high stability, excellent optoelectronic properties, and high absorption coefficient, making it an excellent absorber of sunlight. However, its high defect density leads to the recombination of charges, reducing the overall efficiency of the photovoltaic cell. The research paper cites recent studies on PSCs based on FASnI3 and lead-free Sn, which report PV parameters, i.e., PCE, VOC, JSC, and FF. The optimum structure with PEDOT-WO3 as the HTL, PCBM as the ETL, and FASnI3 as the photon’s absorber layer displayed the best PCE of 17.46% with a Voc of 1.04 V, Jsc of 24.86 mA/cm2, and FF of 67.15%.