Computational Investigation Of Zn-based Single Buffer Layers Toward Cd-free High-efficiency CIGS Thin Film Solar Cells

The photovoltaic performance of copper indium gallium diselenide (CIGS)-based solar cells with Cd-free single buffer layers and a barium disulfide (BaSi2) back-surface field (BSF) has been studied through a numerical approach using a one-dimensional solar cell capacitance simulator (SCAPS-1D). The efficacy of the buffer layer of cadmium sulfide (CdS) via FTO/CdS/CIGS/BaSi2/Mo heterostructure has been studied first and thereafter toxic CdS is replaced by various non-toxic buffers; zinc selenide (ZnSe), indium-doped zinc sulfide (ZnS:In), and indium sulfide (In2S3). Comprehensive research has been performed on the effects of buffer layer thickness, gallium (Ga) concentration in CIGS absorber, BaSi2 BSF doping density, various back contact metals, and cell operating temperature. The highest power conversion efficiency (PCE) of the CIGS-based solar cell with the CdS buffer layer is 26.24 percent, while solar cells with Zn-based buffers made of ZnS:In or ZnSe show improved PCE of 17.68 percent and 17.56 percent, respectively. This study demonstrates the enormous potential of Zn-based ZnS:In and ZnSe buffers for the experimental fabrication of high-efficiency thin-film solar cells with the following structure: FTO/buffer/CIGS/BaSi2/Mo.