Techniques for increasing Ga content in CuIn[sub 1−x]Ga[sub x]Se[sub 2] thin films prepared by two-stage selenization process

Abstract

A Cu-Ga(66 at. %) alloy target was employed for enhancing the gallium content in CuIn1−xGaxSe2 films prepared by two Se-vapor selenizations of metallic precursors. Combination with a Cu-Ga(22 at. %) sputtering target allowed preparation of CuIn1−xGaxSe2 films with a graded profile. Gallium content Gax near the surface was raised to the range 0.28–0.32, while an even higher amount of gallium of up to 0.40 was obtained in the bulk of the films. Efficiency of solar cells prepared from CuIn1−xGaxSe2 films with moderately enhanced gallium content was 8.5%. Higher gallium proportions seem to be correlated with the formation of Cu-rich phases, surface inhomogeneities, and possibly a highly resistive phase. This combined with inferior crystallinity deteriorated solar cell efficiency.