DC Sputtered W-Doped VO₂ Thermochromic Thin Films for Smart Windows with Active Solar Control

Doped VO₂ thin films, with different W at.% and consequent dissimilar transition temperatures, were successfully deposited onto SiO₂-coated float-glass substrates by reactive direct current (DC) magnetron sputtering. Structural analyses have shown, for undoped films, single phase VO₂(M) films with c-axis (002) direction as the preferred crystal orientation. The addition of tungsten into the VO₂ solid solution favored the crystallization in the (011) direction which became dominant above a critical level of dopant concentration. The surface morphology of pure VO₂ films revealed elongated grains oriented within the film plane. The doped films evidenced an increased tendency to be oriented out of the film plane which has resulted in increased roughness levels. The doping methodology associated with optimized processing conditions allowed the production of W-doped VO₂ films with reduced transition temperatures, from 63 down to 28 °C, and maximum transmittances at the visible region ranging 40%. The relationship between tungsten content in the film and consequent transition temperature expressed a linear behavior.