Design and Scalable Synthesis of Thermochromic VO2-Based Coatings for Energy-Saving Smart Windows with Exceptional Optical Performance

We report strongly thermochromic YSZ/V0.855W0.018Sr0.127O2/SiO2 coatings, where YSZ is Y stabilized ZrO2, prepared using a scalable deposition technique on standard glass at a low substrate temperature of 320 {\deg}C and without any substrate bias voltage. The coatings exhibit a transition temperature of 22 {\deg}C with an integral luminous transmittance of 63.7% (low-temperature state) and 60.7% (high-temperature state), and a modulation of the solar energy transmittance of 11.2%. Such a combination of properties, together with the low deposition temperature, fulfill the requirements for large-scale implementation on building glass and have not been reported yet. Reactive high-power impulse magnetron sputtering with a pulsed O2 flow feedback control allows us to prepare crystalline W and Sr co-doped VO2 of the correct stoichiometry. The W doping of VO2 decreases the transition temperature, while the Sr doping of VO2 increases the luminous transmittance significantly. A coating design utilizing a second-order interference in two antireflection layers is used to maximize both the integral luminous transmittance and the modulation of the solar energy transmittance. A compact crystalline structure of the bottom YSZ antireflection layer further improves the VO2 crystallinity, while the top SiO2 antireflection layer provides also the mechanical and environmental protection for the V0.855W0.018Sr0.127O2 layer.