Performance enhancement of CIGS-based solar cells by incorporating an ultrathin BaSi2 BSF layer

Conventional copper indium gallium diselenide (CIGS)-based solar cells offer higher efficiency than other second-generation technologies such as hydrogenated amorphous silicon (a-Si:H)- or cadmium telluride (CdTe)-based solar cells, but higher manufacturing cost due to the use of the rare metals indium and gallium. The purpose of the work presented herein is to improve the efficiency of such devices by using cheaper materials. Accordingly, a back-surface field layer made of low-cost and widely available barium silicide (BaSi2) with a thickness of 0.3 µm is introduced for the first time into the basic CIGS solar cell structure consisting of Al/ZnO/CdS/CIGS/Mo, resulting in the alternative structure of Al/FTO/CdS/CIGS/BaSi2/Mo, with fluorine-doped tin oxide (FTO) as the window layer. One-dimensional simulations of the solar cell capacitance are employed to study the photovoltaic parameters such as the power conversion efficiency, short-circuit current density, open-circuit voltage, fill factor, and quantum efficiency of the devices. The thickness of the CIGS absorber layer is varied from 0.1 to 3 µm to optimize the device. Besides, the effects of the acceptor ion and bulk defect densities in the CIGS absorber layer, cell resistances, and operating temperature on the overall performance are also investigated. The proposed structure offers an efficiency of 26.24% with a thin CIGS layer of only 0.8 µm. In addition to reduced CIGS thickness and cost, the presented approach results in CIGS solar cells with enhanced performance compared with previously reported conventional designs.