Cu(In, Ga)Se₂ thin films prepared from stacked precursors by post-selenization process

The copper–indium–gallium metallic precursors were fabricated corresponding to the sequence CuGa/CuIn/CuGa/soda-lime-glass by sequential direct current magnetron sputtering. The as-sputtered precursors were comprised of Cu₁₁In₉, Cu₁₆In₉, In, Cu₉Ga₄, and CuGa₂ phases, which may be closely correlated to the deposition sequences of multi-layered metallic precursors. Cu(In, Ga)Se₂ (CIGS) absorber films were prepared from the stacked precursors by post-selenization process with solid Se powder, and the morphological, structural, and compositional properties were investigated. The as-selenized CIGS film exhibited a smooth, compact, and densely packed morphology with well-defined and faceted crystal grains. The film was Cu-deficient and had a low Ga content. X-ray diffractometer results indicated the formation of single-chalcopyrite structure CIGS absorber layers. Depth-resolved Raman patterns showed the formation of a dominant CIGS phase in the as-selenized layer, and an ordered vacancy compound phase like Cu(In, Ga)₃Se₅ at the surface and inner region. With increasing the sputtering time, the full width at half maximum of the chalcopyrite A₁ Raman peak increased. Band broadening can be interpreted as a result of a higher density of defects within the chalcopyrite CIGS phase. The A₁ peak shifts with increasing sputtering depths were not apparent, which was related to a uniform distribution of Ga in the CIGS thin film.