Abstract
Solution approaches to NiOx films for electrochromic applications are problematic due to the need of an additional high-temperature annealing treatment step in inert gas. In this study, nanostructured NiOx powder with grain size of about 10.1 nm was synthesized for fabrication of NiOx films for electrochromic application. Non-toxic dispersants of isopropanol and deionized water were used and the whole process was carried out in air. The effects of the number of spin-coating layers, annealing temperature, and the volume ratios of isopropanol to deionized water were systematically investigated. Large transmittance change of 62.3% at 550 nm, high coloration efficiency (42.8 cm2/C), rapid switching time (coloring time is 4 s, bleaching time is 3 s), and good stability were achieved in the optimized NiOx film. The optimized process only required a low processing temperature of 150 °C in air with spin-coating three times and 1:2 volume ratio of isopropanol to deionized water. Finally, good cycle durability of up to 2000 cycles without obvious degradation was demonstrated by cyclic voltammetry tests in a LiClO4/propylene carbonate electrolyte. This study provides a simple and effective approach for fabrication of NiOx films at low temperature in air, which is attractive for further commercialization of electrochromic devices.
Highlights
According to statistics, building energy consumption accounts for 23–50% of total energy consumption [1]
We showed the fabrication of NiOx films with superior optical and EC properties that required low-temperature annealing at 150 ◦ C in air by the spin-coating method
The cathodic and anodic peak current densities (j) of NiOx films annealed at 100 °C and and 150 ◦ C show much lower oxidation and reduction potentials compared to NiOx film annealed at room temperature
Summary
According to statistics, building energy consumption accounts for 23–50% of total energy consumption [1]. Metal oxide material is a big family of inorganic EC materials that have been intensively studied [7,8,9,10,11,12,13] They have excellent radiation resistances, high chemical stability, strong adhesions to substrates, and light weight over large areas [14]. The optimized optical and EC properties of NiO-based films are acceptable in application, there is still one problem that hampers the reduction of fabrication cost and commercialization. High temperature annealing above 300 ◦ C is required to improve the optical and EC properties of NiO-based films. We showed the fabrication of NiOx films with superior optical and EC properties that required low-temperature annealing at 150 ◦ C in air by the spin-coating method. We discussed the microscopic differences between NiOx films to obtain a clear understanding of the differences in EC properties
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