Ga gradient behavior of CIGS thin films prepared through selenization of CuGa/In stacked elemental layers

• CIGS film was formed using a two-stage process.
• Each element of diffusion behavior was investigated.
• The 2.56% conversion efficiency was achieved.

In this study, Cu (In, Ga)Se2 (CIGS) film was formed using a two-stage process. Bilayer CuGa/In metallic precursors were sequentially deposited using both CuGa alloy and In targets in magnetron sputtering. Then, the Se layer was coated on the sputter-deposited CuGa/In precursors through evaporation. The diffusion behaviors of each element during the post-selenization annealing process were determined based on FESEM, XRD, and SIMS. The higher annealing temperature was proposed to have improved Ga diffusion toward the film surface, and thus, achieved the growth of more uniform, more densely packed, and larger grains. Moreover, Na and O contents were found to be correlated due to the strong affinity between Na and O. The distribution of Na seems to be similar to the Ga profile, which may be ascribed to the diffusion of Ga, which was retarded by Na and O. The CIGS films fabricated by the two-step method consisted of a single chalcopyrite phase, and the efficiency of the cell fabricated by the films was 2.56%.