Herein, three different backsurface-filed (BSF) layers “SnS, PbS, and V2O5” are investigated on Mo/BSF/CZTS/CdS/AZO heterojunction solar cells using experimental data of CdS thin films. CdS thin films are produced by means of the pulsed laser deposition (PLD) technique with three different deposition periods. With increasing deposition time, the crystalline sizes of CdS thin films are larger and their crystal structures are developed. In addition, the optical bandgap of CdS thin films is calculated to be 2.4 eV using the absorbance data. Using the solar cell–capacitance–simulator-1D (SCAPS-1D) program, the experimental properties of CdS thin films to estimate the performance of p-CZTS/n-CdS/AZO heterojunction solar cells are introduced. The best efficiency is 9.32% when the thickness of CdS reaches 150 nm. To further improve the efficiency, different BSF layers (SnS, PbS, and V2O5) are tested in Mo/BSF/CZTS/CdS/AZO solar cells. According to the thickness of the BSF layer, the efficiency of the solar cell increases up to 13.47%, 14.7%, and 17.41% using SnS, PbS, and V2O5 as BSF layers with 0.1 μm thickness.