Improvement of the CIGS solar cell performance: structure based on a ZnS buffer layer

Cu(In,Ga)Se2 (CIGS) based thin film solar cells are the most efficient thin-film solar cells today. The non-toxic and wide band-gap zinc sulphide (ZnS) is a promising material to replace the cadmium sulfide (CdS) as the buffer layer in CIGS based solar cells. In this work we present a simulation study of a CIGS based solar cell with a buffer layer of ZnS, using the simulator Silvaco-Atlas. Our primary simulation shows a 22.6% efficiency of the CIGS solar cell with the CdS buffer layer which is comparable to reported and highest experimental results. However, the simulated efficiency of the CIGS solar cell with the ZnS buffer layer as high as 23.54% was achieved. The effects of layer parameters like the thickness, the acceptor and donor densities of the CIGS absorber and ZnS buffer layers and the CBO on the photovoltaic parameters of the ZnS/CIGS solar cell are optimized in order to improve the performance of the ZnS/CIGS solar cell. The highest efficiency of 27.33% is achieved when the ZnS buffer and the CIGS absorber layers have thicknesses of 0.025 µm and 4 µm with acceptor and donor densities of 6 × 1017 cm−3 and 1018 cm−3, respectively and a CBO in the range − 0.05 to 0.05 eV. The present results of simulation can help the development of the solar cells with higher conversion efficiency and low cost.