Increase in conversion efficiency of above 14% in Cu(In,Ga)3Se5 (β-CIGS) solar cells by Na2S incorporation through the surface of β -CIGS film

(a) A schematic three-stage co-evaporation process for Cu(In,Ga)3Se5 (β-CIGS) film with Na2S incorporation at various stages and (b) J-V curves of the β-CIGS solar cell with the best efficiency of 14.2% without antireflective coating by Na2S incorporation on the β-CIGS layer (③).193