Effects of Bi Incorporation on Cu(In1-x,Gax)Se2 Thin Films and Solar Cells

The effects of bismuth (Bi) incorporation into Cu(In1-x,Gax)Se2 (CIGS) thin films and solar cells have been investigated. 10–50-nm-thick Bi thin layers were deposited onto Mo-coated soda-lime glass (SLG) and SiOx-coated SLG substrates by vacuum evaporation. CIGS thin films were then deposited by a three-stage process at substrate temperatures of 450–550 °C. The grain growth of CIGS thin films was enhanced, and the open-circuit voltage and hence the conversion efficiency was improved by the Bi incorporation when the SLG substrates were used. However, little effect was observed when the alkali barrier SiOx layer was deposited on SLG substrates. As a result, we found that the Bi incorporation is beneficial for improving the cell performance when sodium exists simultaneously in CIGS layers.