Optical and Surface Morphology Study of NiO Thin Films for Optoelectronic Applications

Nickel oxide (NiO) thin films were deposited on indium tin oxide (ITO) substrates using a low-cost sol–gel spin-coating technique. The annealing treated NiO films  resulted in uniform and optically transparent films. UV–visible absorption studies showed strong ultraviolet absorption and 90 %  transparency in the visible region. The optical band gap, determined from the Tauc plot assuming a direct allowed transition, was estimated to be 3.35 eV, indicating good optical quality. Atomic force microscopy revealed a continuous, crack-free surface with homogeneously distributed nanoscale grains. The films exhibited a root-mean-square surface roughness of 24.28 nm, which is favorable for efficient charge transport and improved interfacial contact. The combined optical transparency and controlled surface morphology highlight the potential of sol–gel-derived NiO thin films for optoelectronic applications, particularly as hole-transport layers in solar cells and organic light-emitting diode.