radiative cooling

solar absorber

engineering center

poly methyl

porous matrix

electrochromic devices

wafer surface

time-resolved fluorescence

core-shell structure

vanadium oxide

Materials Today Physics

Vanadium dioxide (VO 2 )–based thermochromic films are of great interest for energy-saving smart windows as they can dynamically change the solar transmittance as the ambient temperature changes. However, VO 2 is thermodynamically unstable and could be easily oxidized by the oxygen and moisture in the ambient air. In this work, a durability-enhanced VO 2 nanoparticle-polymer thermochromic film was proposed and fabricated using the blade coating method where the cross-linked and highly entangled poly(methyl methacrylate) (PMMA) chains with a molecular weight (~ 950,000) was adopted to block gas diffusion in the polymer matrix . It was shown that the developed VO 2 nanoparticle film kept ~30% of its solar modulation ability after ~900 h of accelerated durability test in the aging environment with a temperature at 60 °C and ~95% relative humidity . This is ~4 times of the lifetime of the VO 2 nanoparticles which are embedded in the non–cross-linked PMMA matrix with low molecular weight (~15,000). The cross-linked PMMA-VO 2 film also showed a high luminous transmittance of ~50%, a high solar modulation ability of ~17%, and a low haze of ~11%. Our method provides an easy and effective strategy to improve the lifetime of VO 2 nanoparticles, showing a promising pathway toward environmentally stable and easily scalable thermochromic films for energy-efficient smart windows.

Durability-enhanced vanadium dioxide thermochromic film for smart windows