In the current framework, the n-SnO2/n-CdS/p-Si heterostructure was fabricated at differ-ent tin dioxide (SnO2) thicknesses (d = 30, 60, 90, 120, 150, and 180 nm). In this device,nickel (Ni) and platinum (Pt) strips were used as back and front contact electrodes, respec-tively. The structural and optical properties of the SnO2 cap layers were studied. Usinga frequency of 10  MHz, a typical dark capacitance–voltage (C–V) characteristic of thefabticated heterostructure was measured to determine the electronic parameters. In orderto understand the behavior of the fabricated device under dark conditions, the current den-sity–voltage (J–V) characteristics were analyzed. The measurements showed a significantrectifying behavior, demonstrating the junction’s good rectification characteristic. Thedevices’ performance parameters, including open-circuit voltage (Voc), short-circuit currentdensity (JSC), fill factor (FF), and power conversion efficiency (PCE), were all discoveredto be affected by the cap layer’s thickness when subjected to AM1.5 illumination. In thisstudy, the higher thickness window layer had a power conversion efficiency of 14.25%.Remarkably, the addition of a cadmium sulfide buffer layer, and changing the thicknessof the SnO2 cap layer were critical in improving the photovoltaic properties, with the suit-ability of the last SnO2 cap layer confirmed due to its good structural, optical, quantumefficiency 𝜂, spectral photoresponsivity ℜ and photovoltaic properties.