Theoretical simulation of performances in CIGS thin-film solar cells with cadmiumfree buffer layer

Copper indium gallium selenium （CIGS） thin film solar cells have become one of the hottest topics in solar energy due to their high photoelectric transformation efficiency. To real applications, CIGS thin film is covered by the buffer layer and absorption layer. Traditionally, cadmium sulfide （CdS） is inserted into the middle of the window layer （ZnO） and absorption layer （CIGS） as a buffer layer. However, the application of the GIGS/CdS thin film solar cells has been limited because of the environmental pollution resulting from the toxic cadmium atom. Although zinc sulfide （ZnS） has been proposed to be one of the candidates, the performance of such battery cells has not been investigated. Here, in this paper, we systematically study the possibility of using zinc sulfide （ZnS） as a buffer layer. By including the effects of thickness, concentration of a buffer layer, intrinsic layer and the absorbing layer, we find that photoelectric transformation efficiency of ZnO/ZnS（n）/CIGS（i）/CIGS（p） solar cell is about 17.22%, which is qualified as a commercial solar cell. Moreover, we also find that the open-circuit voltage is -0.60 V, the short-circuit current is -36.99 mA/cm2 and the filled factor is -77.44%. Therefore, our results suggest that zinc sulfide may be the potential candidate of CdS as a buffer layer.