As perovskite solar cells near commercialization, concerns about organic and toxic components remain. Inorganic CsSnX3 (X = I, Cl) emerges as a promising alternative due to its eco-friendliness, high carrier mobility, and stability, with a bandgap ranging from 1.3 to 1.55 eV. However, issues such as high carrier concentration, band misalignment, and material defects still exist. This study uses the Vienna Ab initio Simulation Package (VASP) to analyze the crystal and optoelectronic properties of CsSnI3 and CsSnCl3. Both exhibit direct bandgaps of 1.33 and 1.52 eV, respectively, and strong UV–visible absorption (∼105 cm−1), indicating their potential in solar applications. Using one dimensional solar cell capacitance simulator (SCAPS-1D), a novel solar cell structure is designed to harness both sub-bandgap and above-bandgap photons. A low-bandgap absorber is embedded within a high-bandgap layer, forming a straddling-type sandwiched structure. This configuration creates a confined region with a proper conduction band offset, while the surrounding p+/n+ layers generate a strong internal electric field. Key parameters like position, thickness, and barrier height are optimized for carrier transport and minimal recombination. The simulation predicts a theoretical efficiency of ∼34%, indicating the potential of the proposed device architecture to guide future experimental efforts toward realizing enhanced photovoltaic performance.