Mg/W-codoped vanadium dioxide thin films with enhanced visible transmittance and low phase transition temperature

Abstract

Vanadium dioxide (VO₂), with a reversible phase transition near ambient temperature, has been found to be a promising candidate for energy-saving smart windows. However, its use is constrained by its low visible transmission (T_lum) and high transition temperature (τ_c). In this paper, by codoping tungsten (W) and magnesium (Mg) in VO₂, a good combination of low τ_c (∼35 °C) and high T_lum (81.3%) was achieved. The τ_c declines with decreasing Mg doping level in Mg/W-codoped samples, which is the opposite effect of doping with only Mg, suggesting a synergistic effect of the two dopants arising from the e⁻ and h⁺ carrier neutralization. In addition, the band gap of Mg/W-codoped VO₂ was gradually widened; this is attributed to the depressed absorption, which enhanced the T_lum.