Alkali Doping Nickel Oxide Thin Films Using Sol-Gel Spin Coated and Density Functional Theory: Structural and Physical Properties

Experiments are supplemented with ab initio density functional theory (DFT) calculations in order to investigate how the structural, optical and electronic properties of nickel oxide (NiO) thin films are modified upon with 3% alkali (Li, Na, K) doping. Changes in characteristic properties of doped thin films prepared by sol gel spin coating method are monitored using X-ray diffraction (XRD) and UV measurements. All the prepared films were found to be belonging to cubic structure, crystallize preferentially along (200) plane. Optical study based on (UV-Visible) revealed that the band gap tends to decrease with K doping and it achieves a minimal value with Na doping, while it increases with Li doping. The Urbach energy changes symmetrically with the grain size variation. The measurements of the resistivity revealed that alkali doping caused a considerable reduction in the resistivity. 3% Li doped sample had the lowest resistivity value. To elucidate the changes on the optical properties due to presence of dopants 3% alkali (Li, Na, K), we have employed first principle calculations based on density functional theory to calculate the optical properties and the change operated in the band gap due to structural changes. The incorporation of dopants within NiO host lattice affects the lattice parameter and reduced the band gap value. Experimentally observed structural and optical results are in good agreement with our theoretical results.