Synthesis and characterization of highly stoichiometric AgInSe₂ thin films via a sol-gel spin-coating technique

Highly stoichiometric AgInSe₂ thin films have been prepared on a p-type Si(111) substrate by a sol-gel spin-coating technique. These films were annealed at different temperatures. The as-prepared and annealed films were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) and X-ray photoelectron spectroscopy (XPS). The XRD spectra showed that the crystal structure of the AgInSe₂ film was that of cubic fluorite chalcopyrite with lattice constants a = 6.102 Å and c = 11.69 Å. The SEM images depicted the surface morphology as smooth and the spherical particles as uniformly distributed. The average particle size was increased as the annealing temperature increased. Using HRTEM images and SAED patterns for the as-synthesized and annealed thin films, the AgInSe₂ film was indexed to a pure polycrystalline chalcopyrite AgInSe₂ structure with a lattice spacing of around 0.3 nm. XPS spectra showed that the as-deposited AgInSe₂ film was Ag rich, while the AgInSe₂ films annealed at 523 and 623 K were In rich.