Low-temperature rf sputtered VO2 thin films as thermochromic coatings for smart glazing systems

VO2 is a material of great interest due to its excellent thermochromic properties. In this work, Vanadium dioxide (VO2) films were deposited on commercial SnO2-coated glass by the rf magnetron sputtering technique, at the low deposition temperature of Tsub = 300 °C. The effect of thickness and oxygen content in Ar-O2 plasma on the thermochromic properties were studied. In specific, it was found that the critical transition temperature (Tc) remained constant, while the width of transmittance hysteresis loop (ΔTC) was slightly decreased as thickness was increased from 35 nm to 260 nm. In addition, solar/transmittance modulation (ΔTrsol) was increased by about 6%, while luminous transmittance (Trlum) was decreased almost 30%, with thickness. Furthermore, as the oxygen content in the plasma ranged from 2% to 4%, both TC and ΔTC increased about 4 °C, while ΔTrsol and Trlum showed a slight increase of 1% and 3%, respectively. Finally, ZnO antireflective coatings of thicknesses from 22 to 100 nm were deposited on VO2 thermochromic films by dc magnetron sputtering technique at room temperature, in an effort to enhance the luminous transmittance. As a result, an increase in Trlum of over 8%, with a 30 nm ZnO film was observed, while ΔTrsol was increased by about 1%, independent of the ZnO thickness, while both TC and were unaffected by the presence of ZnO antireflective coating.