Electrochromism is a phenomenon in which we can persistently and reversibly change the colour of a material by applying an electric field. The phenomenon involves the insertion and de-insertion of electrons and ions within the electrochromic material. For years, there has been a keen interest in electrochromic materials among researchers since they exhibit a wide range of potential applications, such as smart windows for energy-saving purposes, low-power informational displays, electronic papers, self-dimming rear mirrors for vehicles, and electronic e-skins. In recent years, transition metal oxides have attracted a great deal of attention due to their low power requirement, high colouration efficiency, and memory effect under open-circuit conditions. Nickel oxide (NiO), a p-type wide band-gap semiconductor, exhibits attractive features such as high colour contrast ratio, good chemical stability, cost-effectiveness, and good compatibility with the well-known cathodically colouring tungsten oxide. NiO thin films have been fabricated by various methods, but these are not cost-effective and easily scalable.

In this work, a NiO-based electrochromic layer is developed via a chemical deposition route i.e., electroless nickel deposition, followed by its oxidation. Along with thermal oxidation, room temperature electrochemical oxidation is also demonstrated in this work to make the process suitable for flexible substrates. Electroless nickel deposition can be combined with patterning, which can be used to develop a pixel-based display. The optoelectronic and electrochromic properties of the developed NiO film and their dependence on the deposition and oxidation conditions will be evaluated as part of this work to achieve optimal switching and colour contrast ratio.