In this study, we combined the experimental work performed using a one-dimensional simulation program to simulate the capacity of a solar cell. Simulation can be used to show the real effects of a phenomenon on the target subject, under controlled and regulated conditions. In this here, CdTe based thin film solar cell has been investigated under AM 1.5 ghobal spectrum with using Solar Cell Capacitance Simulator-1D (SCAPS-1D) software. Initially, solar cells with nanostructured FTO/TiO2/n-CdSe/p-CdTe were considered as the elementary cells and FTO/ TiO2/n-CdSe/p-CdSe1_xTex/p-CdTe as the upgraded cells. The purpose of this study was to investigate the key role of layer CdSe xTe 1-x. The results of the analyzes showed that the presence of CdSe xTe1-x nanostructured layer, between p-type CdTe absorber layer and n-type CdSe layer increased PCE from 14.05% to 21.98%, JSC from 20.42. mA/ cm2 to 26.06 mA/cm2, FF from 54.73% to 57.69% and VOC from 1.25 V to 1.46 V compared to the elementary cell.