The effect of copper doping on the structural, optical, and electrical properties of nickel oxide thin films for optoelectronic applications

In this paper, structural, optical, and electrical features of undoped and copper-incorporated nickel oxide (Cu/NiO) films with different mole ratios (0.01, 0.05, 0.1%) were studied. The prepared Cu/NiO films with a thickness of 100 nm were deposited on glass substrates using sol–gel combined with a spin coating technique. The results of X-ray diffraction (XRD) showed that all Cu/NiO films are polycrystalline of a cubic phase with a sharp tip predominating in the (111) direction. The estimated crystallite sizes of the prepared films were found in the range of nanoscale dimensions (19.115, 21.924, 23.057, 26.219 nm) by employing XRD data. Besides, images of the atomic force microscopy (AFM) and scanning electron microscope (SEM) reveal that the surfaces of the Cu-doped NiO films are smooth, holes-free, cracks-free, and homogeneous with dense fullness. Fourier transform infrared (FTIR) findings demonstrated that the emergence of the two chemical bonds located at 400–500 cm−1 attributed to Ni–O stretching vibration. However, the results did not show any evidence about the emergence of the Cu–O bond due to the weak copper concentration in the samples. Moreover, prepared films showed high optical transparency (94%) in the range of visible region and decreased to 92% with an addition of 0.1% Cu, which confirms the possibility of using them as window layers in solar cells. Finally, the electrical measurements showed that the surface resistance of NiO film decreased significantly after Cu doping. Our results could pave a good opportunity for providing insight into Cu-doped NiO properties and their usage in optoelectronic applications.