Facile preparation of black electrochromic ink using a copper oxide nanoparticle suspension

Electrochromic (EC) materials for smart windows must exhibit a dark colour and block visible light (wavelength = 380–780 nm) to reduce environmental impact. Many researchers have attempted to use organic materials like polymers to produce these dark tones. However, their fabrication methods are complicated, expensive, and may even use hazardous substances; moreover, they are often not sufficiently durable, such as upon exposure to ultraviolet light. Therefore, herein we focused on using copper oxide (CuO) to develop an ecofriendly, inexpensive dark inorganic EC thin film by printing ink prepared using our nanoparticle (NP) dispersion technology. Specifically, we dispersed CuO NPs, synthesised by simply heating basic copper carbonate, in easily purified water using citric acid to adjust the pH. This research will enable the creation of EC smart windows using existing inorganic materials and methods, such as printing technology, and is the first step towards developing environment-friendly, cost-effective, and functional dark inorganic materials.