The effect of pressure on the structural and optical properties of CdO thin films deposited by chemical spray pyrolysis on a moving substrate

CdO thin films were deposited using chemical spray pyrolysis (CSP) over a dynamic substrate travelling at 6 cm/s, at pressures between 1.0 and 2.5 bar. The research investigated the influence of deposition pressure on the structural, morphological, and optical characteristics of the films. X-ray diffraction (XRD) verified the existence of cubic CdO crystals, exhibiting a principal peak at 33° associated with the (111) plane. Elevated pressure diminished crystallite size from 60.43 nm to 18.49 nm, concurrently augmenting micro strain and lattice distortion as a result of internal stress. Scanning Electron Microscopy (SEM) examination corroborated these findings, demonstrating a transition from big irregular grains to smaller compact grains with increasing pressure. The dynamic substrate improved film transparency by enhancing homogeneity and minimizing agglomeration, resulting in a more uniform grain distribution. Optical investigation demonstrated a clear correlation between structural alterations and optical efficacy. The film deposited at 1 pressure demonstrated 85% transmittance, which diminished to 40% at 2.5 bar as a result of heightened grain density and flaws. The optical band gap decreased from 2.17 eV to 2.00 eV with elevated pressure, due to enhanced crystallinity and a rise in defect states. Fluctuations in the absorption coefficient and refractive index corresponded with structural and morphological analyses. This research emphasizes the significance of pressure regulation in enhancing CdO films for use in transparent conductive oxides, photodetectors, and solar cells.