A Comparative Performance Evaluation of Ternary ZnxCd1-xS and Binary CdS window Layer in CIGS Solar Cell

Abstract

Among other thin film solar cells, as like as cadmium telluride (CdTe) or amorphous silicon (a-Si), CIGS thin film solar cell has been very well recognized in recent years due to its high market share and superior light absorption quality. CdS is a widely used material as buffer layer or window layer in conventional CIGS solar cell. However, CdS is extremely poisonous, putting the environment in jeopardy, and it has a low bandgap (2.42ev), making light absorption in the main CIGS layer tougher. To solve this problem, a concept of ternary compound has been brought out which is an alloy of CdS and ZnS.  In this research work, a thin film CIGS cell is numerically studied with a ternary compound Zn_xCd_1-xS as window layer in lieu of of binary compound CdS by SCAPS 1D simulator. Zn_xCd_1-xS is an admixture of CdS and ZnS that rises the band gap between 2.42ev to 3.7ev which leads to a fine absorption in the blue region (400-500nm). The cell performance is numerically examined by changing the function x from 0.05 to 0.3 with absorber layer thickness (1000 to 2000nm) and window layer thickness (10 to 300nm). To enrich the overall cell performance, two additional layers of In₂S₃ and BaSi₂ have been added as buffer layer and back surface field (BSF) layer or electron reflector layer in this proposed cell. The thickness of the In₂S₃ buffer layer (50 to 200nm), as well as the thickness of the BaSi₂ BSF layer (100 to 1000nm) and the bandgap of the buffer layer (2.1 to 2.5ev) were used for numerical evaluation in order to achieve a high efficiency of this cell. For x=0.1 and a window layer thickness of 10nm, the recommended structure Zn_xCd_1-xS/CIGS has the highest efficiency of 29.42% when compared to conventional CdS/CIGS cell. For experimental purpose, window layer Zn_xCd_1-xS thickness has been fixed at of 50nm at which cell power conversion efficiency has been obtained 29.00% for the proposed Zn_xCd_1-xS/CIGS cell which is also greater than the conventional CdS/CIGS cell.