CuZnSnSe (CZTSe) is a brilliant material for solar energy systems because its essential elements, non-toxic nature, and suitable bandgap for solar energy conversion are abundant on Earth. This compound exhibits a chalcopyrite structure, which is conducive to effective light absorption and charge carrier mobility. The efficiency of solar cells, especially thin-film types, is significantly impacted by three main types of losses: optical losses, recombination losses, and electrical losses. This paper has studied theoretically the effect of electrical losses resulting from series and shunt resistance on the performance of CdS/CZTSe solar cells. Cell efficiency, fill factor, open circuit voltage, and short-circuit current density have been accurately estimated. It was found that the Values of series and shunt resistance have a significant influence on the cell performance. An increase in series resistance from 0 Ω to 25 Ω causes a dramatic decrease in fill factor from 0.803 to 0.360 and a drop in efficiency from 16% to 7%, alongside a slight reduction in open circuit voltage. Conversely, increasing shunt resistance from 2000 Ω to infinity improves the fill factor and raises efficiency modestly from 15.5% to 16%. However, maintaining fixed resistance values leads to an upward shift in performance curves, with a slight decrease in open-circuit voltage and efficiency. These results underscore the importance of optimizing resistance parameters to enhance solar cell performance and efficiency.