Impacts of Sb and Bi incorporations on CIGS thin films and solar cells

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 SiO_x-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 SiO_x 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.