In this work, thin-film solar cells based on Cadmium Selenide (CdSe) film were used, due to the low manufacturing cost and superior electronic properties, and this type of cell also achieves appropriate efficiency. The current work will focus on investigating the effect of the thickness and carrier concentration of the active layers in the cell, and the thickness of the window on the performance of the proposed solar cell, using the one-dimension solar cells capacitance simulation SCAPS-1D computer program. The proposed structure of this cell consists of ITO/n-CdSe/p-CdSe/Pt, where ITO was used as a window layer, n-CdSe as a buffer layer, p-CdSe as an absorber layer, and platinum Pt as a back conductive electrode. The results revealed that the cell performed best at thicknesses of 5000 and 100nm for the absorber and buffer layers, respectively, and with carrier concentrations of 1016 and 1017cm-3for the same layers. The optimal window layer thickness is 100nm. These variables yield open circuit voltage (VOC), short circuit current density (JSC), fill factor (FF) of 1.0845 V, 20.87 mA/cm2, 88.02% respectively, while the conversion efficiency of cell (Eff.) was obtained, which is 19.92%.