IR electrochromic WO3 thin films: From optimization to devices

This paper reports enhanced electrochromic properties in the infrared region, so-called IR, and in particular, in the middle wavelength (MW: 3–5 μm) and long wavelength (LW: 8–12 μm), of radio frequency sputtered (RFS) WO3 thin films, thanks to a careful optimization of the deposition conditions, namely the duration of deposition (<240 min), the substrate nature (FTO or Au), and the chamber pressure (15 and 45 mT). Significant modulations in reflectance (as high as 73% in the MW) and in the apparent temperature (up to 35 °C) between the inserted state and the deinserted one, for WO3 thin films cycled in H3PO4 liquid electrolyte, are reported. Such performances correspond to a variation in emissivity of at least 40% as required for military applications. Finally, coupling both modelling and experimental approaches, first trends on the incorporation of the WO3 single layer in full electrochromic devices (ECDs) are discussed considering mainly an all-solid-state device configuration.