Opto-structural, electrical and electrochromic properties of crystalline nickel oxide thin films prepared by spray pyrolysis

Article abstract of DOI:10.1016/S0921-4526(01)01024-9

Polycrystalline nickel oxide films with preferential growth along (1 1 1) plane were deposited onto glass substrates, maintained at 350°C, by the spray pyrolysis technique using nickel chloride as starting solution. The effect of solution concentration on their structural, electrical, and optical properties was studied. Using X-ray diffraction, the structural characteristics have been studied and due to the high degree of preferred orientation, Voigt analysis of single reflection was used to determine the microstructural properties (crystallite size and microstrain). The refractive index n and the extinction coefficient k have been computed from the corrected transmittance and reflectance measurements over the spectral range 300-2400 nm. Analysis of the absorption versus photon energy curves revealed a direct transition with optical band gap, E_g, of 3.6 eV and indirect transition within the range 3.97-3.75 eV as solution molarity increases from 0.05 to 0.3 M. The electrochromic behaviour of polycrystalline nickel oxide film were investigated by means of cyclic voltametry in 1 M KOH aqueous solution. Cycling showed significant increase in solar optical modulation reaching a value of 0.23 after 150 cycles.