Real-time studies of phase transformations in Cu–In–Se–S thin films: 1. Intermetallic phase transformations

Phase transformations of CuxIn thin films were investigated in annealing experiments using real-time in situ energy dispersive X-ray diffraction (EDXRD). Cux  In films of micrometer thickness with x=0.7x=0.7, 1.0, and 1.8 were annealed up to 500 °C. The experiments were designed in order to form a basis for the understanding of the phase transformations relevant for chalcogenization of CuxIn films. The starting layers for the in situ study consist of CuIn2 and Cu, i.e. all In are accumulated in an intermetallic phase. Depending on the In content in a film, the volume fraction of the CuIn2 phase varies. The main phase transformations in the annealing cycle can be described by the following reaction schemes: (1) 11CuIn2→Cu11In9+13Insolid, (2) 16Cusolid+9Inliq→η-Cu16In9 (or (2′) 7Cusolid+9Inliq→Cu7In3), and (3) 16Cu11In9→11η−Cu16In9+45Inliq. At top temperature, rapidly changing diffraction patterns point out rapid transitions between different metastable polytypes of Cu16In9. Metallic phases observed at room temperature after quenching are η-Cu16In9, Cu11In9, and Insolid where the respective volume fractions depend on the starting film composition.