Study the effect of strontium and copper co-doping on the structural, morphological, and optoelectronic properties of nickel oxide thin films

This work presents the effect of co-doping of strontium (Sr) and copper (Cu) on the properties of nickel oxide (NiO_x) thin films. 3 wt.% of Cu and various compositions (1, 2, and 3 wt.%) of the Sr were successfully co-doped in the NiO_x. Thin films of NiO_x co-doped with Sr and Cu were deposited on a fluorine-doped tin oxide (FTO) conductive substrate using a solution-processed spin coating technique. Their evolution of structural, morphological, and optoelectronics properties were studied by using X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive x-rays analysis (EDX), ultraviolet–visible spectroscopy (UV–VIS), and Hall effect measurement system. XRD analysis confirmed the crystalline, cubic phase structure and exhibited direction along the (200) plane. SEM demonstrated that all the samples have homogeneous and pinhole-free surfaces. UV–visible spectroscopy demonstrates that with the increase in concentrations of Sr, the transparency of the thin film reduced from 85% to 78%. The band gap of NiO_x reduces from 3.78 eV to 3.73 eV by increasing the concentration of dopant (Sr 1–3 wt.% and Cu 3 wt.%). The most improved band gap of 3.73 eV was achieved with a co-doping of 3 wt.% Sr and 3 wt. % Cu in NiO_x. The Electrical conductivity of NiO_x was improved by adding the dopant due to the replacement of Ni ions by Sr and Cu. The optimum conductivity (5.67 × 10^–5 (1/ Ω-cm)) was achieved at Sr (2 wt.%) and Cu (3 wt.%). As a result of improved electrical conductivity Sr, and Cu co-doped NiO_x thin films can be used in different types of optoelectronic and photovoltaic applications, such as organic light-emitting diode (OLEDs), gas sensors, electrochromic devices, and solar cells.