Nickel Oxide Films Deposited by Sol-Gel Method: Effect of Annealing Temperature on Structural, Optical, and Electrical Properties

In our study, transparent and conductive films of NiOx were successfully deposited by sol-gel technology. NiOx films were obtained by spin coating on glass and Si substrates. The vibrational, optical, and electrical properties were studied as a function of the annealing temperatures from 200 to 500 °C. X-ray Photoelectron (XPS) spectroscopy revealed that NiO was formed at the annealing temperature of 400 °C and showed the presence of Ni+ states. The optical transparency of the films reached 90% in the visible range for 200 °C treated samples, and it was reduced to 76–78% after high-temperature annealing at 500 °C. The optical band gap of NiOx films was decreased with thermal treatments and the values were in the range of 3.92–3.68 eV. NiOx thin films have good p-type electrical conductivity with a specific resistivity of about 4.8 × 10−3 Ω·cm. This makes these layers suitable for use as wideband semiconductors and as a hole transport layer (HTL) in transparent solar cells.