Investigation of Structural and Optical Properties of Zinc Sulfide Nanoparticles Synthesized via Chemical Route for Photovoltaic Applications

Zinc sulfide is a wide-bandgap II-VI semiconductor with significant potential as a buffer layer material in thin-film solar cells due to its favorable band alignment, low toxicity, and Earth-abundant composition. This study investigates the structural and optical properties of zinc sulfide nanoparticles synthesized by chemical precipitation using zinc acetate and thiourea precursors at varying reaction temperatures of 50, 70, and 90 degrees Celsius and reaction durations of 30, 60, and 90 minutes. Synthesis was conducted at the Nanomaterials Research Laboratory of the University of Benin, Edo State, South South Nigeria. Structural characterization was performed using X-ray diffraction, with crystallite size estimated by Scherrer equation analysis of peak broadening. Transmission electron microscopy was used to determine particle morphology and size distribution. Optical properties including direct bandgap energy, Urbach energy, and extinction coefficient were derived from UV-Vis diffuse reflectance spectroscopy using the Tauc and Kubelka-Munk transformation methods. Results indicate that increasing synthesis temperature from 50 to 90 degrees Celsius reduces mean crystallite size from 8.4 nm to 4.2 nm while simultaneously increasing phase purity of the cubic zinc blende structure. Optical bandgap values ranged from 3.52 eV to 3.74 eV, exhibiting quantum confinement blue-shift relative to the bulk bandgap of 3.54 eV, consistent with sub-10 nm particle sizes. The study evaluates the suitability of produced nanoparticles as buffer layers in CdTe and CIGS thin-film solar cell architectures based on measured band alignment. Keywords: zinc sulfide nanoparticles, optical properties, chemical synthesis, photovoltaic, bandgap