Non-toxic selenization using thermal annealing for CuGa/In bi-layer precursors deposited by sputtering

Cu(In_xGa_1-x)Se₂ (CIGS) thin films were produced using a two-step sputtering process consisting of precursor formation and selenization. In the first stage, we prepared Cu_0.75Ga _0.25/In bi-layer precursors by direct current sputtering on Mo/soda-lime glass substrates. In the second stage, the stacked precursors were selenized using non-toxic Se pellets in a graphite box in which the temperature was controlled at 475-680 °C during rapid thermal annealing. We investigated the effect of thermal annealing temperature on Ga distribution and the crystallinity of the Cu(In_xGa_1-x)Se₂ films. Thermal annealing significantly affected the distribution of Ga atoms. At low temperatures, segregation of Ga atoms into the CIGS/Mo interface and an absence of Ga content on the surface were observed. In addition, a phase-separated CuInSe₂/CuGaSe₂ structure and incomplete selenization phases were observed. At high temperatures, CIGS films were formed with the proper distribution of Ga content.