Lead-free perovskite solar cells have attracted global research interest due to their tunable band gaps, optical properties, and environmental friendliness. In this work, we computationally studied KSnI₃ perovskite solar cells. This was achieved by investigating the impact of using LiTiO₂, ZnO, SnO₂, and AlZnO as electron transport layers coupled with rGO as a hole transport layer. The optimization of the thicknesses and dopant densities of individual layers yielded PCEs of 27.60%, 24.94%, 27.62%, and 30.44% for of FTO/Al-ZnO/KSnI₃/rGO/Se, FTO/LiTiO₂/KSnI₃/rGO/Se, FTO/ZnO/KSnI₃/rGO/Se, and FTO/SnO₂/KSnI₃/rGO/Se solar cell configurations, respectively. Thus, our FTO/SnO₂/KSnI₃/rGO/Se device is almost 8 % more efficient than FTO/SnO₂/3C-SiC/KSnI₃/NiO/C, which is currently the most efficient KSnI₃ perovskite solar cell structure in the literature. Thus, our FTO/SnO₂/KSnI₃/rGO/Se perovskite solar cell structure is now, by far, the most efficient PSC design. Its best performance is achieved under ideal conditions of zero series resistance, shunt resistance of 10⁷ Ω cm², and a temperature of 371 K. In this presentation, I will reveal the details of the aforementioned results and how the approach used in this study can be applied, in future studies, not only to other perovskite solar cells, but also to other types of solar cells such as solid-state dye-sensitized solar cells to significantly improve their efficiency.