Stability of CdTe/CdS thin-film solar cells

The recent literature regarding the stability of CdTe/CdS photovoltaic cell s las distinguished from modules) is reviewed. Particular emphasis is given to the role of Cu as a major factor that can limit the stability of these devices. Cu is often added to improve the ohmic contact to p-CdTe and the o verall cell photovoltaic performance. This may be due to the formation of a Cu2Te/CdTe back contact. Excess Cu also enhances the instability of device s when under stress. The Cu, as Cu+, from either Cu2Te or other sources, di ffuses via grain boundaries to the CdTe/CdS active junction. Recent experim ental data indicate that Cu, Cl and other diffusing species reach (and accu mulate at) the CdS layer, which may not be expected on the basis of bulk di ffusion. These observations may be factors in cell behavior and degradation , for which new mechanisms are suggested and areas for future study are hig hlighted. Other possible Cu-related degradation mechanisms, as well as some non-Cu-related issues for cell stability are discussed. (C) 2000 Elsevier Science B.V. All rights reserved.