High thermochromic performance of Fe/Mg co-doped VO2 thin films for smart window applications

Abstract

In the field of energy-efficient smart windows, vanadium dioxide (VO₂) is a promising material due to its reversible metal–insulator transition. However, the development of VO₂-based smart windows has been restricted by several drawbacks in performance, including high phase transition temperature (T_C), low luminous transmittance (T_lum), insufficient solar energy modulation ability (ΔT_sol) and unpopular color. In this paper, Fe/Mg co-doping is proposed for the first time to improve the thermochromic performance of VO₂ films. Interestingly, the Fe/Mg co-doped films can exhibit outstanding thermochromic performance with a balanced solar regulation efficiency of 12.8%, suitable luminous transmittance up to 42.1%, and low phase transition temperature around 38.2 °C, which is very promising for practical applications. In addition, the color of films is modified to increase their brightness and lighten the brown color. Different from previous work on co-doped VO₂ focusing on W⁶⁺ and low-valence (<4+) elements, Fe³⁺/Mg²⁺ co-doping is found to have the synergistic combination of the advantages of single doping with Fe and Mg by getting rid of the neutralization between charge carriers e⁻ and h⁺. Such a feature is especially desired for optimizing the thermochromic performance with co-doping methods. This study provides a new solution for improving the optical properties of VO₂ films for smart window applications.