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

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 (tau(C)). In this paper, by codoping tungsten (W) and magnesium (Mg) in VO2, a good combination of low tau(C) (similar to 35 degrees C) and high T-lum (81.3%) was achieved. The tau(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.