Fabrication of metal chalcogenide thin films by a facile thermolysis process under air ambient using metal-3-mercaptopropionic acid complex

We report a facile and low-cost solution-based approach to synthesize various binary, ternary and quaternary metal chalcogenide thin films. Homogeneous metal chalcogenides single precursor is prepared by dissolving metal salt (metal chloride/acetate) in ethanolic/methanolic solution of 3-Mercaptopropionic acid (MPA) at room temperature. High-quality CdS, ZnS, Sb₂S₃, CuInS₂ (CIS) and Cu₂ZnSnS₄ (CZTS) metal sulfide thin films are successfully synthesized by thermalizing these metal-MPA precursor solution at 350 °C in air for 15 min. The mechanism of metal sulfide formation is analyzed by FTIR and thermogravimetry coupled with mass spectrometry. This study highlights the formation of intermediate metal-MPA complex as a single precursor, which eventually decomposes into metal sulfide upon heating at 350 °C. The film thickness, morphology and composition of metal sulfide can be controlled by the concentration of reactants, deposition cycles and the choice of solvent. XRD, Raman, UV–vis spectroscopy, diffuse reflectance spectroscopy and energy dispersive analyses ascertain the phase purity of the films. Bandgap estimates, morphology, narrow Urbach width with low defect densities in the bandgap region, uniform thickness discerned from cross-section SEM, uniformity in the elemental maps and the photoconductivity studies further confirm high-quality of the films. Attaining molecular-level homogeneous precursor solution and inertness to the air ambient enables precise control on the stoichiometry and the enhanced uniformity of deposited films. This facile method will have potential application in large scale synthesis of different metal chalcogenide thin films by a thermolysis process and is highly suitable for controlling stoichiometry and spatial uniformity of deposited films sought in solar cell, optoelectronic and catalysis applications.