Topics on thin film CdS/CdTe solar cells

Abstract

Efficient thin film CdS/CdTe solar cells can be prepared by the close-spaced sublimation technique onto soda-lime glass coated with either indium tin oxide or tin oxide. Oxygen is needed to enhance the p characteristics of CdTe; a high substrate temperature is needed to reduce the interfacial defects at the CdS/CdTe junction. Cells with gold electrodes are not stable owing to AuCdTe interaction. Alternative electrodes to CdTe can be prepared by using a HNO 3-H 3PO 4 surface treatment. The cells whoed 30–40% efficiency degradation when aged over 2 years at 100 °C under continuous air mass 1 illumination. The degradation appears to result from a decrease in the carrier concentration with aging. The aging process is not sensitive to ambience but is sensitive to the presence of light or voltage bias. It is believed to be related to the dependence of the effective carrier concentration on the cooling rate subsequent to the CdTe deposition. Defect interaction may be a possible cause of the aging behavior but photoluminescence and deep-level studies have not established the mechanism involved. The evidence suggests that trace impurities can have significant effects on the behavior of the cells and could be responsible for the aging behavior.