SURFACE OXIDATION OF POLYCRYSTALLINE CADMIUM TELLURIDE THIN-FILMS FORSCHOTTKY-BARRIER JUNCTION SOLAR-CELLS

Polycrystalline CdTe thin films grown on graphite or tungsten-coated g raphite substrates by chemical vapor deposition (CVD) were exposed to the air at room temperature in a natural atmosphere of about 60% air h umidity for 6 months. X-ray photoemission spectroscopy (XPS) and Auger electron spectroscopy (AES) of the films indicate that a tellurium di oxide (TeO2) overlayer has formed from this process. The effects of su ch an overlayer on the electrical property of polycrystalline CdTe-bas ed Schottky barrier junction solar cells have also been discussed for the first time. It is shown that a solar cell formed on a CdTe film wi th TeO2 overlayer has considerably higher open-circuit voltage and fil l factor than that formed on a CdTe film without TeO2 overlayer. Our s tudy further indicates that using a polycrystalline CdTe film which is thermally oxidized at above room temperature (100-400 degrees C) does not provide any improvement on the solar cell efficiency.