Lead-based perovskite solar cells suffer from toxicity and inadequate stability, driving the pursuit of lead-free alternatives. In this work, a comprehensive modeling analysis was conducted on lead-free A₃SbI₃-based (A=Ba²⁺, Sr²⁺, Ca²⁺) solar cells using SCAPS-1D simulation. Twelve initial device architectures were designed with Ca₃SbI₃, Sr₃SbI₃, and Ba₃SbI₃ as photoactive layers, SnS₂ as the electron transport layer, and MoO₃, Spiro-OMeTAD, Cu₂O and P3HT as hole transport layers, respectively. Energy level alignment and interfacial energetics analysis reveal MoO₃ as the optimal hole transport layer due to its superior band matching with the photoactive layer. Consequently, the three devices with superior performance among the initial models, FTO/SnS₂/Ca₃SbI₃/MoO₃/Au, FTO/SnS₂/Sr₃SbI₃/MoO₃/Au and FTO/SnS₂/Ba₃SbI₃/MoO₃/Au, were selected for performance evaluation and parameter optimization. The simulation work systematically analyzed the impact of the thickness, defect density, and doping concentration of the photoactive layer on the photovoltaic performance of the solar cells. Based on the analysis of simulation results, the QE of the devices improves as the thickness of the photoactive layer increases, leading to a progressive increase in J_sc. However, excessive thickness promotes carrier recombination, resulting in a reduction in V_oc and FF. Increasing the thickness of the photoactive layer leads to a reduction in total impedance due to the enhanced carrier concentrations, although this occurs at the expense of extended recombination paths. When the photoactive layer thickness reaches 700 nm, all three devices attain their maximum PCEs. The higher defect density in the photoactive layer leads to a decrease in recombination resistance and exacerbates non-radiative recombination. When the defect density of the photoactive layer is maintained at 10¹⁴ cm^-3, the devices achieve superior photovoltaic performance. Elevating the acceptor doping concentration of the photoactive layer enhances the built-in electric field and reduces the charge transfer resistance, thereby facilitating efficient hole extraction and improving the V_oc and the FF. The V_oc exhibits a more pronounced sensitivity to the acceptor doping concentration of the photoactive layer compared to the J_sc. To achieve optimal photovoltaic performance, the doping concentration should be maintained above 10¹⁵ cm^-3, with the devices exhibiting superior performance at a concentration of 10¹⁷ cm^-3. Under identical conditions, the Ca₃SbI₃-based device exhibits the highest V_oc, whereas the Ba₃SbI₃-based device shows the lowest V_oc. Conversely, the Ca₃SbI₃-based device demonstrates the lowest J_sc, while the Ba₃SbI₃-based device achieves the highest J_sc. Ca₃SbI₃ possesses the widest bandgap, while Ba₃SbI₃ exhibits the narrowest bandgap. The narrower bandgap of Ba₃SbI₃ enables a broader spectral response and enhanced photon-to-current conversion, thereby yielding the highest J_sc. Among the three devices, the Ca₃SbI₃-based device exhibits the lowest carrier recombination rate, leading to its highest V_oc. Following systematic parameter optimization, the devices achieved significantly enhanced photovoltaic performance. The Ca₃SbI₃-based, Sr₃SbI₃-based, and Ba₃SbI₃-based devices exhibited PCE improvements of 37.40%, 52.01%, and 71.29%, respectively, highlighting the great potential of these antimony-based perovskites for high-efficiency solar harvesting. This work provides a theoretical foundation for the development of high-efficiency, thermally stable, and eco-friendly perovskite solar cells.