Cu(In,Ga)Se 2 Thin Films Codoped with Sodium and Bismuth Ions for the Use in the Solar Cells

The codoping effects of sodium and bismuth ions on the characteristics of Cu(In,Ga)Se 2 films prepared via the solution process were investigated in this study. When sodium and bismuth ions were incorporated into Cu(In,Ga)Se 2 , the ratio of the intensity of (112) diffraction peak to that of (220/204) diffraction peak was greatly increased. The codoping process not only enlarged the sizes of the grains in the films but also resulted in densification of the films. The carrier concentration of Cu(In,Ga)Se 2 was found to be effectively increased to cause a reduction in the resistivity of the films. The above phenomena were attributed to the densified microstructures of the films and a decrease in the amount of the donor‐type defects. The leakage current of the solar cells was found to be also decreased via the codoping process. Owing to the improved electrical properties of Cu(In,Ga)Se 2 films, the conversion efficiency of the fabricated solar cells was significantly enhanced.