Eco-friendly lead-free perovskite CH ₃ NH ₃ SnI ₃ (MASnI ₃ ) based solar cell device was simulated using the one-dimensional solar capacitance tool (SCAPS 1D). In this work, we investigate the effect of several parameters such as the thickness and the defect density in the absorber layer. We focus on the effect of defect densities at the TiO ₂ /MASnI ₃ , MASnI ₃ /Spiro-OMeTAD interfaces on the photovoltaic performances. Our results show that the best performances were obtained with an absorber thickness layer kept of 1.1 μ m, and for low defect densities in the active layer and at the TiO ₂ /MASnI ₃ interface. In addition, we have studied the effect of various hole transport layers (HTL) compounds such as Cu ₂ O, CuO, CuI, CuSCN, PTAA, PEDOT: PSS, and MEH-PPV. Our results show the significant impact of valence band offset and hole mobility on device performances. The champion device has a power conversion efficiency of 27.77%, a current density ( J _sc ) of 34.6 mA cm ⁻² , an open circuit voltage ( V _oc ) of 0.96 V and a fill factor of 83.34%. This work can provide imperative guidelines to researchers for the design of efficient eco-friendly perovskite solar cells.