Near-infrared-activated VO2 based nanothermochromic smart windows by incorporation of photothermal W18O49 nanorods

VO 2 -based thermochromic smart windows have attracted much attention due to their promising energy-saving effects. However, the high phase transition temperature ( T c , 68 °C), low luminous transmittance ( T lum , <40%) and solar energy modulation efficiency (Δ T sol , <10%) hindered their practical application. In order to improve these deficiencies simultaneously, the photothermal W 18 O 49 nanorods were introduced into VO 2 based nanothermochromic films in this work. The obtained film exhibited enhanced thermochromic performance ( T lum  = 82.5%, Δ T sol  = 10%) due to the incorporation of W 18 O 49 nanorods. And T lum of 63.3% and Δ T sol of 18.6% were presented for the bilayer film, which is one of the best reported performances for VO 2 films to date. In particular, the bilayer film exhibited an obvious energy saving effect with a reduction of 21.1 °C in indoor temperature compared with normal glass due to its excellent thermochromic properties. In addition, the thermochromic characteristics of VO 2 -W 18 O 49 -polyvinylpyrrolidone (PVP) composite films could be trigged at lower temperature than that of VO 2 film due to the additional thermal energy generated by the absorption of near-infrared light by W 18 O 49 nanorods. Therefore, the outstanding performance and the easily scaled solution-based synthesis route would facilitate the practical application of VO 2 -based smart windows.