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 T-sub = 300 degrees C. The effect of thickness and oxygen content in Ar-O-2 plasma on the thermochromic properties were studied. In specific, it was found that the critical transition temperature (T-C) remained constant, while the width of transmittance hysteresis loop (Delta T-C) was slightly decreased as thickness was increased from 35 nm to 260 nm. In addition, solar/transmittance modulation (Delta Tr-sol) was increased by about 6%, while luminous transmittance (Tr-lum) was decreased almost 30%, with thickness. Furthermore, as the oxygen content in the plasma ranged from 2% to 4%, both T-C and Delta T-C increased about 4 degrees C, while Delta Tr-sol and Tr-lum showed a slight increase of 1% and 3%, respectively. Finally, ZnO antirefiective 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 Tr-lum of over 8%, with a 30 nm ZnO film was observed, while Delta Tr-sol was increased by about 1%, independent of the ZnO thickness, while both T-C and were unaffected by the presence of ZnO antirefiective coating.