Optical design and stability study for ultrahigh-performance and long-lived vanadium dioxide-based thermochromic coatings

In this work, thermochromic Cr2O3/VO2/SiO2 (CVS) sandwich structures on glass substrates were designed and fabricated by magnetron sputtering method. Optical design and calculation were employed to optimize the structure using a optimization program. The bottom Cr2O3 layer provides a structural template for improving the crystallinity of VO2 and increasing the luminous transmittance of the structure. Then, the VO2 layer with a monoclinic (M) phase at low temperature undergoes a reversible phase-transition to rutile (R) phase at high temperature for solar modulation. The top SiO2 layer not only acts as an antireflection layer but also greatly enhances the environmental stability of the multilayer structures as well as providing a self-cleaning layer for versatility of smart coatings. According to optical measurements, the fabricated CVS multilayer structure exhibits excellent optical performance with ultrahigh solar modulation ability (Delta T-sol = 16.1%) and an improved luminous transmittance (T-lum,T-lt = 54.0%), which is nearly the maximum simulation value for VO2-based multilayer thin coatings. Meanwhile, stability and deterioration as well as relative mechanisms of the VO2 coatings were also investigated by monitoring the valence change of the vanadium element. The proposed structure shows remarkable environmental stability due to the dual-protection from the Cr2O3 and the SiO2 layer, which shows negligible deterioration even after accelerated aging of 10(3) h and 4*10(3) fatigue cycles, while VO2-single layer samples almost become invalid. Finally, energy-efficient effect was successfully demonstrated using CVS coated glass as the roof of a winter garden.