Sn dopants improve the visible transmittance of VO2 films achieving excellent thermochromic performance for smart window

Abstract

How to achieve high visible-light transmission meanwhile maintain satisfying solar modulation (ΔTsol) remains a challenge for VO2-based thermochromic smart windows. In this study, Sn dopants exhibit the ability of enhancing the visible transmittance (Tlum) of VO2 films, as a result, endowing the films with excellent thermochromic properties. Sn-doped VO2 films with different Sn contents (0at%, 0.43at%, 0.74at%, 1.73at%, 1.86at%) are prepared via hydrothermal method. The 0.74at% Sn-doped film has a Tlum value about twice that of the undoped film. The improvement of the visible transmittance is rationalized by ellipsometry and optical absorption measurements, in which it is revealed that the Sn dopants reduce the refractive index (n) and extinction coefficient (k) of VO2 in the VIS-NIR wavelength range, and widen the band gap (Eg). The 0.74at% Sn-doped VO2 film realizes excellent thermochromic performance with the ΔTsol up to ~15.4% and the Tlum reaching ~51.8%. This work demonstrates the unique characteristic of Sn dopants to improve the visible transmittance of VO2 films, suggesting a rational way in optimizing the thermochromic property of VO2.