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.