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

Abstract

We report strongly thermochromic YSZ/V_0.855W_0.018Sr_0.127O₂/SiO₂ coatings, where YSZ is Y-stabilized ZrO₂, prepared by using a scalable deposition technique on standard glass at a low substrate temperature of 320 °C and without any substrate bias voltage. The coatings exhibit a transition temperature of 22 °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, fulfills the requirements for large-scale implementation on building glass and has 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 codoped 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 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 V_0.855W_0.018Sr_0.127O₂ layer.