Buffer layer replacement: A method for increasing the conversion efficiency of CIGS thin film solar cells

The performance of the buffer layer of CIGS thin film solar cell was optimized using SCAPS software to improve the conversion efficiency. In the first step, the validity of empirical and simulation models were verified. After that, four buffer layers of InS, ZnS, ZnO and ZnSe were substituted with CdS in the Glass/Mo/CIGS/CdS/ZnO/ZnO:Al nanostructure. The results indicated that the Zn-based compounds are proper substitute buffer layers with similar electronic and physical properties due to higher band gap than CdS. Next, the effect of buffer layer thickness was investigated and the optimum thicknesses of buffer layers was achieved. Results revealed that zinc selenide with efficiency of 20.07% can be an appropriate alternative buffer layer for CdS. Also, it is shown that by optimizing the buffer layer thicknesses, the solar cell efficiency raises, mainly due to increase in fill factor.