Effect of Zr and W Doping on Microstructures, Transition Temperature and Solar Transmittance Modulation of Thermochromic W/Zr Co-Doped VO 2 Thin Films

Abstract

Thermochromic W/Zr co-doped VO 2 -based thin films with different concentrations of Zr were successfully deposited on soda lime glass substrates by direct current (DC) magnetron sputtering of V(99)W(01) alloy and Zr targets at a substrate temperature of 425 °C. The films were characterized by x–ray diffraction (XRD), atomic force microscopy (AFM), Rutherford backscattering spectroscopy (RBS), two-point probe and UV/VIS/NIR spectroscopy. The film’s structural properties evolution was significantly influenced by Zr concentration in the films. The transition temperature and hysteresis loop widths of the films were found to decrease with increasing Zr concentration. For the Zr concentrations of 0.21 at.%, 0.23 at.% and 0.36 at.% the films’ transition temperatures were 38.1 o C, 35.7 o C and 33.7 o C, respectively, whereas the corresponding hysteresis widths were 12.9 °C, 5.7 °C and 2.6 °C. Films with 0.36 at.% Zr demonstrated a high value of solar transmittance modulation at 8%, albeit with some compromise in luminous transmittance. These results reveal that a controlled amount of Zr in the W-doped VO 2 films can potentially improve the films' thermochromic properties for smart Windows applications.