Recently, the solar energy sector has been greatly interested in lead (Pb)-free inorganic halide perovskites due to their remarkable mechanical, optical, electronic, and structural characteristics. Our study comprehensively assessed these attributes in cubic A3SbI3(A = Ba, Sr, Ca) perovskite materials via first principles density functional theory (FP-DFT) and SCAPS-1D simulation. These materials, similar to lead-free inorganic metal halide perovskites, demonstrated favorable tolerance factors, direct bandgaps, mechanical robustness, minimal losses, and high absorption coefficients. We aimed to explore how A-cation size influences their properties and solar cell performance, enabling effective comparisons. We systematically investigated novel A3SbI3-based structures with tin (IV) sulfide (SnS2) buffers, varying layer thickness, doping density, and defect density to evaluate photovoltaic (PV) capabilities. The Ba3SbI3 absorber exhibited the highest power conversion efficiency (PCE) at 30.26% with JSC of 44.24 mA/cm2, FF of 85.65%, and VOC of 0.80 V, while Sr3SbI3 and Ca3SbI3 absorbers achieved PCE of 26.93% and 20.87%, respectively, with corresponding JSC of 34.5 and 21.87 mA/cm2, FF of 86.90% and 85.85%, and VOC of 0.90 and 1.11 V. Our A3SbI3-based solar cell structures offer innovative alternatives to conventional designs. [ABSTRACT FROM AUTHOR]