Structural and optical transmittance analysis of CuO thin films deposited by the spray pyrolysis method

Nano-sized CuO thin films were deposited onto glass substrate using the chemical spray pyrolysis method. These films were characterized using the x ray diffraction (XRD), Raman spectroscopy and UV–visible spectroscopy. The characterization results were investigated as a function of the spray number. According to the XRD patterns, all the deposited films were polycrystalline monoclinic CuO. The XRD result was confirmed by Raman spectroscopy. The lattice parameters remains mainly constant and the (002)-oriented crystallite size increased from 4 to 6 nm. From the transmittance spectra, the band gap energy decreased from 2.14 to 1.85 eV and the mean transmittance between 400 and 800 nm decreased from 35 to 5%. The decrease of the band gap energy as a function of the increasing crystallite size was explained by the quantum confinement effect.