Electrical and optical properties of sol–gel-deposited NiO films and corresponding response to annealing temperature

The electrical and optical properties of sol–gel deposited nickel oxide (NiO) films are studied as a function of the annealing temperature. NiO X films are successfully obtained by spin coating process on glass and silicon substrates, and their transparency and conductivity have been improved using sol–gel technology. Further, the vibrational, optical, and electrical properties of NiO X film are investigated concerning annealing temperatures between 150 and 450 °C. From the investigation, annealing at 350 °C results in the formation of NiO, and through X-ray Photoelectron Spectroscopy (XPS), it evidences the existence of Ni3 + which is confirmed along with Ni 2+ state. Furthermore, when the NiO X samples are treated at 150 °C, their optical transparency in the visible region reaches 90%, and when the temperature is increased to 450 °C, the optical transparency drops to 75–78%. Through investigation, it is also identified that the optical band gaps get reduced to the region of 3.93–3.67 eV through thermal treatments. From the investigation, it is identified that thin films are excellent p-type electrical conductors having a specific resistivity of around 4.8 × 10 3 Ω/cm. Hence, they can be used in the manufacturing of transparent solar cells such as Hole Transport Layers (HTLs) and wideband semiconductors.