Fabrication and Characterization of Eggshell-Derived Nano-CaO Thin Films as Anti-Reflective Coatings: Morphological and Optical Properties

Abstract

Light reflection from glass surfaces reduces the amount of solar radiation transmitted into photovoltaic devices, making transparent thin-film coatings an important approach for improving optical transmission. This study investigated the preparation of calcium oxide (CaO) thin films derived from waste chicken eggshells through a simple and sustainable synthesis route. Eggshell powders were calcined at temperatures ranging from 800 to 1100°C, and the resulting CaO was deposited onto glass substrates by spin coating using five precursor concentrations, followed by post-annealing at 300°C. FTIR and XRD analyses confirmed the gradual decomposition of CaCO₃ into crystalline CaO with increasing calcination temperature. The sample calcined at 1100°C exhibited higher crystallinity (80.86%) and a larger crystallite size (19.24 nm) than that calcined at 1000°C. SEM observations indicated that post-annealing reduced the film thickness and produced a more uniform surface morphology. UV–Vis measurements showed that the 0,05 M precursor concentration and has the average thickness of 18,92 nm yielded the highest optical transmittance. The thin film prepared from CaO calcined at 1100°C and post-annealed at 300°C achieved a maximum transmittance of approximately 88% in the visible region (400–900 nm), which was higher than that of the uncoated glass substrate (85%). These results indicate that thermal treatment and precursor concentration significantly influence the structural and optical properties of eggshell-derived CaO thin films, highlighting their potential as transparent coating materials for photovoltaic glass