Fabrication of Cu(In,Al)(S,Se)2 films by sulfurization and selenization of co-sputtered Cu-In-Al precursors

Cu(In,Al)(S,Se)2 (CIASSe) films were prepared on soda lime glass substrates by sulfuring and selenizing co-sputtered Cu-In-Al metal precursors. CIASSe film preparation was optimized and the film properties were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, and ultraviolet-visible spectroscopy. Films that were annealed for 20 min formed a single-phase chalcopyrite structure, and those films annealed at 500 °C and 540 °C exhibited a smooth and dense surface topography. After being annealed at 450-540 °C, films contained reduced amounts of copper and close to ideal stoichiometric compositions. Their absorption coefficients were over 104 cm−1, and the obtained optical band gap values were 1.37 eV, 1.42 eV, and 1.44 eV, respectively, which were close to the ideal optical band gaps for photovoltaic applications.