Enhanced visible and tunable infrared transmittance of W-doped VO2/SiO2/PVP composite films for smart windows

Abstract

As a thermochromic material, vanadium dioxide (VO 2 ) has great application potential in smart windows. It has always been the focus of research to improve the visible light transmittance (T lum ) and solar modulation ability ( Δ T s o l ) while reducing the phase transition temperature (T c ) of VO 2 . To achieve this goal, tungsten-doped VO 2 nanoparticles (W-VO 2 NPs) with a T c of 34 °C were used to form composite films with polyvinylpyrrolidone (PVP) by a simple method. High Δ T s o l of 14.2% was obtained at the optimized volumetric concentration of W-VO 2 and film thickness. The W-VO 2 /SiO 2 /PVP composite films were proposed to further improve T lum and Δ T s o l . Compared with the W-VO 2 /PVP composite film with the same thickness and volumetric concentration of W-VO 2 , T lum of the film is increased by 19.3% (from 54.5% to 65%) with the introduction of SiO 2 microspheres, while the Δ T s o l is maintained satisfactorily at 12.6%. This is mainly due to the monolayer dispersed SiO 2 microspheres providing optical pathways in the film, which greatly improves T lum with a slight sacrifice of Δ T s o l . Indoor temperature of a scale-model room with W-VO 2 /SiO 2 /PVP film-coated glass was 9.1 °C lower than that with blank glass due to the isolation effect of metallic W-VO 2 on near-infrared radiation. This work provides a new strategy for promoting the development of VO 2 thermochromic smart windows. • Effect of W-VO 2 volumetric concentration and thickness of film on thermochromic performance were studied and optimized. • Comprehensive thermochromic performance was enhanced by the local surface plasma effect of W-VO 2 . • The improvement of solar modulation ability by increasing volumetric concentration of W-VO 2 nanoparticles is limited. • SiO 2 microspheres were introduced as optical pathways to enhance transmittance of visible light.