Effect of varying deposition and substrate temperature on sublimated CdTe thin-film photovoltaics

A standardized process used for fabrication of CdTe solar cells was varied by increasing the substrate temperature during CdTe layer nucleation from approximately 460°C to 610°C and by increasing the CdTe sublimation vapor source temperature. Higher substrate temperatures increase device efficiency, but cause significant CdS re-sublimation. This effect was eliminated by using a Mg1-xZnxO window layer that also has higher transparency. Elevated CdTe source temperatures were found to increase contamination in the deposition system but did not further improve device efficiency. The improvement using high substrate temperatures is attributed to larger CdTe grains and better crystalline quality. TEM cross section analysis, X-ray diffraction measurements and device results are presented.