Post-annealing effects on the structural and optical properties of nickel vanadate thin films.

Abstract

Abstract This research gap is to understand the post-annealing-temperature-dependent structural transition and defect-mediated optical tuning in NiV₂O₆ thin films deposited using a spin-coating technique. By systematically correlating phase evolution, oxygen vacancy formation, and band gap modulation. The as-prepared thin films were annealed at 200 °C, 300 °C, 400 °C, and 500 °C. The annealing temperature of 400 °C was found for an amorphous structure with the band gap of 2.38 eV, which within an appropriate band gap of ∼ 2.3–2.6 eV for photoelectrochemical and electrochromic applications. Tuning of improved crystallinity with structural rearrangement and a lower band gap of 2.10 eV were obtained at 500 °C, which induced the diffusion of oxygen atoms and led to the formation of oxygen vacancies. This provides a clear processing–structure–optical property correlation and offers a simple-thermal route for band gap engineering without additional doping for enhancing the optical efficiency in solar absorber, optoelectronic, and photonic applications, particularly in broadband optical devices.