Nontoxic, lead-free perovskites have gained significant attention in recent years due to their potential environmental benefits. This numerical study investigates the application of a novel perovskite material, KSnI3, as the absorber layer in solar cell devices due to its high absorption coefficient in the visible photon energy range. Four different electron transport layers (ETLs), including CdZnS, PC${}_{61}$BM, SnS2 and SrTiO3 (STO), along with ten different hole transport layers (HTLs), including PTAA, CNTS, C6PcH2, MoO3, MoS2, C6TBTAPH2, GaAs, TiO2, Cu2Te and D-PBTTT-14, are investigated to develop various distinct combinations. The study begins by optimizing the HTL, after which four distinct combinations using the selected HTLs and the ETLs were made for further numerical analysis. Several device parameters, including HTL acceptor density, absorber layer thickness, defect density and donor density, were optimized to enhance device efficiency. Following optimization, the device configuration of FTO/PC${}_{61}$BM/KSnI3/D-PBTTT-14/Au was identified as the champion, with a power conversion efficiency (PCE) of 22.28%, an open-circuit voltage ($V_{\text{OC}})$ of 1.382V, a short-circuit current density ($J_{\text{SC}})$ of 18.435mA/cm2 and a fill factor (FF) of 87.44%. Additionally, the effects of temperature, series resistance, shunt resistance, generation and recombination rates, JV characteristics, capacitance, Mott-Schottky analysis and quantum efficiency (QE) are observed following the device parameter optimization. These significant findings from this theoretical study are expected to guide future experimental research on KSnI3 perovskite, potentially leading to the development of KSnI3-based perovskite solar cells.