Structure, optical and electrochromic properties of NiO thin films

Nickel oxide thin films were prepared by sol–gel dip coating process. Nickel acetate tetrahydrate [Ni(CH3COO)2·4H2O] has been used as the starting material with absolute ethyl alcohol to prepare NiO thin films on both glass and indium tin oxide glass (ITO) substrates with heat treatment at different annealing temperatures from 673 to 733 K. Thermogravimetric analysis (TGA) was studied for the xerogel sample. Polycrystalline structures of the prepared films were detected by X-ray diffraction analysis (XRD), and the particle size was determined by Scherrer formula. The morphology and the structure of the prepared thin films were investigated by the transmission electron microscope (TEM). The optical properties of NiO thin films were examined. The optical constants such as the absorption coefficient (α), extinction coefficient (k), the energy gap (Eg) and the refractive index (n) of the prepared films were determined. The effect of annealing temperature on the electrochromic behavior was observed providing that good electrochromic performance was T<713 K.