Facile synthesis of Cu <inf>2</inf> ZnGeS <inf>4</inf> thin films from binary metal sulfides and study of their physical properties

In this work, we report the synthesis of Cu 2 ZnGeS 4 (CZGS) thin films using a paste of binary metal sulfides by doctor blade technique. The precursor to deposit the films was obtained by mixing appropriate amounts of CuS, ZnS and GeS with triethanolamine and dilute acetic acid. Initially, the effect of annealing temperature on the phase formation was investigated using the films developed with the precursor containing stoichiometric ratios of metal sulfides. Based on the results obtained for structural and compositional properties of the films using the stoichiometric precursor we further proceeded with the fabrication of Cu-poor CZGS films by varying the binary sulfide concentrations in the precursor. CZGS films deposited with precursor molar ratio, CuS:ZnS:GeS = 1.6:1.2:1, resulted in [Cu]/([Zn] + [Ge]) and [Zn]/[Ge] ratios, 0.77 and 1.21, respectively. Formation of polycrystalline CZGS tetragonal structure was confirmed by X-ray diffraction and the Raman spectroscopy. Scanning electron microscopy revealed flake-like morphology along with pyramidal shaped crystals. The optical band gap of the films was around 1.8 eV. The films were photosensitive and exhibited one order increase in photoconductivity under 100 mW/cm 2 illumination. The fabrication of Cu-poor CZGS films is reproducible by upscaling the amounts of binary sulfides and dispersing medium which provides an attractive option for cost-effective deposition over large area.