Structural, optical and electrical properties of undoped and Li-doped NiO thin films prepared by sol–gel spin coating method

• NiO and NiO:Li thin films are prepared on a glass substrate by sol–gel technique.
• The effects of thickness on the physical properties of NiO are studied.
• Effect of Li doping on the structural, optical and electrical properties of the films.
• Li doped NiO films can be used as transparent conductors.

Un-doped and lithium doped nickel oxide thin films have been prepared on glass substrates by the sol–gel spin coating technique using nickel acetate and lithium chloride as source materials. The thickness of the films was increased by increasing the number of layers successively deposited on the same substrate. The effect of the number of layers on the structural, optical and electrical properties of NiO thin films was studied. The results of investigations of the samples show that four is the most suitable number of layers of undoped NiO films with high optical transparency. Then, by using these optimized deposition parameters, lithium doped nickel oxide films are prepared. The surface morphology and crystalline structure of the thin films were investigated by atomic force microscopy and X-ray diffraction (XRD), respectively. A modification in the morphology of the films was observed while increasing the Li amount in the solution. XRD patterns show that the films are polycrystalline. The preferred orientations were evaluated from XRD data. The average transmittance of the NiO films in the visible region increases with the increase of Li concentration. The electrical measurements show that the resistance of the films decreases as the lithium content increases.