Multifunctional overcoats on vanadium dioxide thermochromic thin films with enhanced luminous transmission and solar modulation, hydrophobicity and anti-oxidation

Vanadium dioxide (VO2) has a great potential to be utilized as solar energy switching glazing, even though there exist some intrinsic problems of low luminous transmittance (T-lurn) and poor oxidation resistance. Si-Al based anti-reflection (AR) sol-gel coatings processed at low temperature have been developed to tackle these issues assisted by adjusting ramping rate and annealing temperature. Si-Al based AR coating gives large relative enhancement on the transmittance (22% for T-lurn, 14% for the whole solar spectrum T-sol,) and successfully maintains IR contrast at 2500 nm wavelength with 18% relative increase in solar modulation (Delta T-sol). The optimized Si-Al based AR coating annealing conditions are recorded at 3 degrees C/min ramping rate and 100 degrees C annealing temperature. Fluorinated-Si based gel offers a new direction of multifunctional overcoat on thermochromic smart windows with hydrophobicity (contact angle 111 degrees), averaged 14% relatively increased luminous transmittance and enhanced oxidation resistance. (C) 2013 Elsevier B.V. All rights reserved.