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

Abstract

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.