Dielectric and Optical Properties of Co-doped Nickel Oxide Nanostructures for energy storage and solar cells by hydrothermal method

Nickel Oxide and Cobalt-doped Nickel Oxide nanoflower were prepared by hydrothermal technique. XRD patterns reveal that pure and Cobalt-doped NiO shows cubic/Rhombohedral crystal structure with space group of Fm-3m. As incorporation of Co content, the crystallinity decreases, crystallite size decreases and is minimum for 5 wt. % Co-doped also micro strain increases which has value of 2.09×10-3, 2.1×10-3, 2.2×10-3 and 2.3×10-3 for pristine, 1 wt. %, 3 wt. % and 5 wt. % Co-doped NiO. SEM images show flower-like morphology for NiO, sphere-like morphology for 1 wt. % Co-doped, rod-like morphology for 3 wt. % Co-doped and ellipsoidal-like morphology for 5 wt. % Co-doped NiO. EDX analysis shows elemental composition of prepared samples. When Co content increases the Oxygen content decreases, oxygen vacancies increase (high defect density). In 5 wt. % Co-doped NiO have high defect density due to small crystal size and small amount of Oxygen. FTIR analysis shows the formation of Nickel Oxide. Ultra Voilet-Visible absorption spectra of Cobalt-doped Nickel Oxide show an absorption peak at 340 nm. When Co content increases the absorption becomes high and is maximum for 5 wt. % Co due to small crystal size, high defect density as well as the bandgap energy decreases. The band gap for pristine, 1 wt. %, 3 wt. % and 5 wt. % Co-doped is calculated to be 3.28, 3.16, 3.04 and 2.90eV respectively. The PL emission is highest for 5 wt. % Cobalt-doped Nickel Oxide due to small crystal size, high defect density (high number of oxygen vacancies) as confirmed in (XRD, EDX) and high absorption in UV-Vis. Dielectric properties are used to study the microstructure of prepared samples. Due to the small crystallite size and the dielectric constant shows dispersion behavior, its value is at its highest for 5 wt. % Co-doped NiO, (SCP) and increasing in hopping mechanism between Co+2/Co+3. With increasing Co concentration, the dielectric loss decreases which shows that 5% Co-doped would be used for charge storage. As Increasing Co concentration causes a sudden shift in conductivity at higher frequencies, demonstrating the suitability of 5 wt% Co-doped NiO for high-frequency devices.