Low-cost WO3 nanoparticles / PVA smart photochromic glass windows for sustainable building energy savings

In this paper, we investigate the WO3-x/PVA composite films as smart photochromic coatings on glass substrate by two methods: solvent casting (SC) and dip-coating (DC). The two methods were thoroughly compared using experimental and theoretical means. All prepared films have been optically investigated by ex-situ and in-situ UV–Vis spectrometry, leading to insight on their coloring/bleaching amplitudes and kinetics. It was found that the SC films exhibited the best photochromic amplitude with a visible and infrared optical contrast ΔCvis=34.37 and ΔCIR=7.9, whereas ΔCvis and ΔCIR reached less than 20.2 and 5.4 for the best films issued from the DC process. Further, a two-flux model (KubelkaMunk) was adapted to understand the associated impacts of absorption and scattering in our composite films. The calculations revealed that the simulated scattering factor was higher in the case of the DC films than for the SC films, explaining hence the higher photochromic amplitude of the latter. After carefully analyzing the relationship between the SC and DC films characterizations and optical performance, we concluded that the SC method offered films that are a better candidate for post-optical application in terms of scattering reduction, improved visible/infrared contrast, and better photochromic efficiency. Nevertheless, the “thick” SC films get a slightly lower kinetic response than the “thin” DC films. Finally, the cooling effect of the photochromic SC films was tested by integrating them in a model wooden room under the irradiation of an artificial solar source. The photochromic SC smart windows proposed here are equally efficient while being more affordable than electrochromic panels or VO2 thermochromic thin films to reduce the inner house temperature (almost 20 °C) upon solar irradiation, demonstrating their great potential as smart cost-effective energy-saving materials •WO3-x/PVA composite films with high visible transparency (low particle scattering).•WO3-x/PVA composite films with efficient and reversible photochromic effect.•WO3-x/PVA composite films significantly limiting inner house temperature upon solar irradiation.