Significance of Substrates and Buffer Layers in CDTE Thin Film Solar Cell Fabrication

CdTe is considered as a viable absorber material for the thin film solar cell because of its excellent material characteristics as well as simple, low cost manufacturability. Despite a theoretical 29% efficiency prediction of the cell, its high work function and coefficient of thermal expansion (CTE) have limited its efficiency to around 17%. One of the remedies of the problem is using a pseudo contact layer, which is called buffer layer in its back contact structure. In this study, different types of buffer layers have been investigated for possible application. Sb2Te3 and ZnTe have been deposited on top of different substrates (Mo, PI) by RF magnetron sputtering and the effects on the deposited films were studied in terms of their structural and morphological forms. In both cases, Sb2Te3 and ZnTe show better performance on top of molybdenum (Mo) sputtered on polymide (PI) rather than molybdenum (Mo) sputtered on molybdenum (Mo) substrate. SEM characterization reveals larger grain sizes as found in Mo sputtered on PI and some cracks were observed in case of Mo sputtered on Mo. However, after CdCl2 treatment CdS surface exhibits larger grain size on top of Mo substrate. While using ZnTe as the buffer layer making it much more advantageous for CdTe solar cells.