Fabrication of an electrochromic device by using WO ₃ thin films synthesized using facile single-step hydrothermal process

The development of an uncomplicated process for the preparation of tungsten oxide (WO ₃ ) nanorods (NRs) using hydrothermal method is still underway. Thus, this study demonstrated the growth of WO ₃ NRs on indium tin oxide (ITO) coated glass substrates in aqueous solution using single synthesis step hydrothermally. The surface area and size of the NRs which should be tunable for electrochromic (EC) applications were controlled by adjusting the concentration of surfactants such as propylene glycol (PG). The synthesized NRs were illustrated using crystal structure study, surface morphology, chemical analysis, and the measure of the luminance of a color. The results manifested that increasing the PG content increased the size of the crystallite with a nanoparticle-like morphology on the ITO substrate, indicating the direct deposition of a stable WO ₃ thin film. In addition, the synthesized WO ₃ NRs exhibited fast switching speed and high contrast ratio implying superior EC properties for smart window application. Furthermore, an EC device with the dimensions of 2 × 4 cm ² was assembled using the synthesized WO ₃ NRs with the ITO/WO ₃ /Lithium perchlorate-propylene carbonate-poly(methyl methacrylate)-acetonitrile/nickel oxide/ITO configuration. The device had an average optical modulation in the visible region, a fast EC response time (1.2 s for coloration and 1.5 s for decoloration), excellent coloration efficiency (243 cm ² C ⁻¹ ) and a superior EC stability (over 20,000 color/decolor cycles).