Significant improvement of the performance of ZrO2/V1-xWxO2/ZrO2 thermochromic coatings by utilizing a second-order interference

Abstract

The paper deals with VO2-based thermochromic coatings prepared by reactive magnetron sputtering. We combine four ways how to improve the coating performance and to increase its application potential. First, reactive high-power impulse magnetron sputtering with a pulsed O2 flow control allowed us to prepare crystalline VO2 of the correct stoichiometry under highly industry-friendly deposition conditions: without any substrate bias at a low deposition temperature of 330 °C. Second, doping of VO2 by W (leading to V1-xWxO2, with x = 0.012 in this work) allowed us to shift the thermochromic transition temperature towards the room temperature (39 °C in this work), without concessions in terms of coating properties. Third, we employ ZrO2 antireflection layers both below and above the thermochromic V1-xWxO2 layer, and present an optimum design of the resulting ZrO2/V1-xWxO2/ZrO2 coatings. Most importantly, we show that while utilizing a first-order interference on ZrO2 leads one to a tradeoff between the luminous transmittance (Tlum) and the modulation of the solar transmittance (ΔTsol), utilizing a second-order interference allows one to optimize both Tlum and ΔTsol in parallel. Fourth, the crystalline structure of the bottom ZrO2 layer further improves the VO2 crystallinity and the process reproducibility. The optimum experimental values of ZrO2 thickness are in agreement with those predicted during the coating design. The results are important for the design and low-temperature fabrication of high-performance durable thermochromic VO2-based coatings for smart window applications.