The effects of antimony (Sb) and bismuth (Bi) incorporation into CIGS thin films and solar cells have been investigated. 10~50 nm-thick Sb or Bi thin layers were deposited onto Mo-coated sodalime glass (SLG) and SiOx-coated SLG substrates by vacuum evaporation. CIGS thin films were then deposited by three-stage process at substrate temperatures of 400-550 °C. The enhanced grain growth of CIGS thin films was observed, and the open-circuit-voltage (V oc ) and hence the conversion efficiency improved by the Sb (Bi) incorporation only when the SLG substrates were used. However, almost no effect was observed when the alkali barrier SiOx layer was deposited on SLG substrates. These results suggest that the benefit by the Sb (Bi) incorporation does not occur by itself, but is a synergistic effect together with the sodium diffused from SLG.
Highly transparent Cu2O thin films on transparent conducting oxide on a glass substrate were fabricated using reactive sputtering by carefully controlling the O2 flow. The impurity dependence of transmittance was thoroughly investigated, and the transmittance was found heavily depending on impurities in Cu2O thin films as confirmed by x-ray diffraction analysis. A highly transparent Cu2O thin film was fabricated using precisely impurity-controlled Cu2O thin films. The effects of impurities in a Cu2O thin film on photovoltaic properties were studied. A maximum efficiency of 8.4% was observed in the lowest-impurity Cu2O thin film.
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