Morphology of precursors and CuIn_1−xGa_xSe₂ thin films prepared by a two‐stage selenization process

The morphology of sequentially sputtered metallic precursors and CuIn_1−xGa_xSe₂ thin films prepared using a novel two‐stage selenization process was found to change from initially very smooth layers with a root‐mean‐square (rms) surface roughness of <10 Å to coalescing grains with a fine (∼200 Å) subgrain structure, three‐dimensional ∼9000 Å size islands, and finally to compact, well‐faceted, large ∼1 μm grain‐size CuIn_1−xGa_xSe₂ thin films with a rms roughness of 950–1500 Å. In situ homogenization of Cu‐rich precursors prior to the first selenization and a maximum selenization temperature of 550–560 °C that provided beneficial fluxing action of copper selenide improved the morphology of completed CuIn_1−xGa_xSe₂ thin films and the photovoltaic conversion efficiency of the solar cells.