Influence of oxygen partial pressure on the structural, optical and electrochromic properties of NiO thin films grown by magnetron sputtering

Nickel oxide (NiO) thin films were grown on glass substrate by direct current magnetron sputtering at different oxygen (O2) partial pressure. The influence of O2 partial pressure on the structural, optical, and electrochromic properties of NiO thin films were investigated. A strong relation between O2 partial pressure and NiO film properties such as optical transparency, crystallinity, grain size, lattice constant and the electrochromic properties was realized. The evaluation of the X-ray diffraction peaks indicated an increase with the in-plane lattice constant with the direction of (200) resulting in a strain on the NiO films. Both Ni2+ and Ni3+ were observed in NiO thin layers from X-ray photoelectron spectroscopy results and their concentration varied according to the O2 partial pressure. Optimization of O2 partial pressure led to reach the highest electrochromic efficiency of 53 cm2/C and optical transmittance variation of 51%.