Efficiency Enhancement of CIGS Solar Cells with the Appropriate Combination of CdS and CdSe Buffer Layers: Simulation by Silvaco Software

The buffer layer is one of the main elements in the thin film solar cells, especially in the copper indium gallium selenide (CIGS) thin-film solar cells. The buffer layer increases the optical absorption and decreases the surface recombination, which in turn results in further absorption of carriers and the enhancement of the solar cell efficiency. In this paper, the cadmium sulfide (CdS) and cadmium selenide (CdSe) thin films were selected as buffer layers. Then, the effect of different combinations of these two buffer layers on the solar cell parameters such as JSC, VOC, FF, and η were investigated using Silvaco Atlas commercial software. The optimal condition and higher efficiency were achieved when the CdS and CdSe layers were close to the ZnO and CIGS layers respectively. It was found out that the selection of 40-nm thickness for cadmium sulfide and 10-nm thickness for cadmium selenide increased the efficiency of solar cell up to 25.19%. Also, the plotting of the energy band diagram illustrated that electrons and holes, in an optimal condition, moved easily without any potential barriers. This condition led to a significant increase in the solar cell efficiency.