SCAPS-1D, a one-dimensional solar cell simulator, provides a valuable tool for predicting device performance based on layer-by-layer material properties. Copper Zinc Tin Sulfide (CZTS) has emerged as a promising absorber material due to its exceptional light absorption coefficient and the abundance and non-toxic nature of its constituent elements. This study leverages SCAPS-1D to investigate the working mechanism of CZTS-based solar cells. We simulate a Mo/CZTS/CdS/ZnO device structure under AM 1.5 spectrum illumination and 300 K temperature, analyzing the impact of individual layer thickness on photovoltaic performance. Further, a comparative analysis explores the influence of various n-type materials. In addition, the introduction of antimony (Sb) doping into CZTS leads to a significant change in efficiency of the cell. The efficiency of Sb-doping CZTS attained 21.90%, while there was a great improvement by 3% via reduced recombination losses and enhanced photocurrent. This work gives an insight into the possibility of Sb doping for the improvement in the performance of thin-film solar cells.