Lead halide perovskites (PVTs) have been demonstrated as emerging absorber materials for photovoltaic (PV) applications. The vulnerable nature of PVT materials under air ambient, heat, and light hindered the commercialization of PVT-based solar cells (PSCs). Thus, Sr substitution is carried out to improve the stability and performance of the PSCs. Here, a numerical simulation was carried out to optimize the performance of MASraPb1−aI3−xClx (a = 0 – 0.20)-based PSCs using SCAPS-1D software. The short circuit current density is enhanced with an increase in the thickness of the PVT layer, however, the open circuit voltage and fill factors are reduced. The performance is increased from 18.27 % (a = 0) to 23.14 % (a = 0.20) for the optimized PVT thickness of 700 nm. A slight reduction of short circuit current density is observed for increasing the defect density of the absorber layer up to 1 × 1015 cm−3, however, a sharp Jsc reduction is observed for higher defect density. The defect density of the PVT layer greatly influences the performance of the PSCs. No significant change in the performance of the PSCs is observed with varying thicknesses of the charge transport layers. Furthermore, the passivated MASraPb1−aI3−xClx perovskite layer can provide stable and highly efficient devices.