Environmentally friendly synthesis and characterization of CuInS₂ thin films via electrostatic spray deposition of nanocolloids

• PVP-capped CuInS 2 nanoparticles were synthesized by thermolysis. • The nanocolloids of CuInS 2 nanoparticles was stabilized in ethanol. • The CuInS 2 absorber layer deposited by Electrostatic spray deposition method . • The deposition of the thin film was a low temperature and non-vacuum method. This study investigates the process parameters for electrostatic spray deposition of a stable colloid derived from copper indium sulfide composition. The research evaluates the influence of coating parameters on film deposition, structure, microstructure, and optical absorption properties. Analytical techniques including optical microscopy, scanning electron microscopy, X-ray diffraction, and ultraviolet-visible spectroscopy were employed. CuInS₂ colloid was deposited using the electrospray method with applied voltages of 24, 26, and 28 kV, flow rates of 1, 2, and 3 µL/min, and nozzle-to-substrate distances of 60, 80, and 100 mm onto fluorine-doped tin oxide glass substrates. Post-deposition, heat treatment at 500 °C was conducted to enhance crystallinity and adhesion, with sulfur powder added to ensure positive sulfur vapor pressure and prevent sulfur loss. Microstructural analysis via optical microscopy, scanning electron microscopy, and field-emission scanning electron microscopy identified best deposition conditions: 26 kV voltage, 2 µL/min flow rate, and an 80 mm nozzle-to-substrate distance, producing a uniform 1 µm-thick layer. The CuInS₂ layer exhibited strong visible light absorption, with an absorption edge at 760 nm and an energy gap of 1.5 eV.