Facile and Low-Temperature Fabrication of Thermochromic Cr₂O₃/VO₂ Smart Coatings: Enhanced Solar Modulation Ability, High Luminous Transmittance and UV-Shielding Function

Abstract

In the pursuit of energy efficient materials, vanadium dioxide (VO₂) based smart coatings have gained much attention in recent years. For smart window applications, VO₂ thin films should be fabricated at low temperature to reduce the cost in commercial fabrication and solve compatibility problems. Meanwhile, thermochromic performance with high luminous transmittance and solar modulation ability, as well as effective UV shielding function has become the most important developing strategy for ideal smart windows. In this work, facile Cr₂O₃/VO₂ bilayer coatings on quartz glasses were designed and fabricated by magnetron sputtering at low temperatures ranging from 250 to 350 °C as compared with typical high growth temperatures (>450 °C). The bottom Cr₂O₃ layer not only provides a structural template for the growth of VO₂ (R), but also serves as an antireflection layer for improving the luminous transmittance. It was found that the deposition of Cr₂O₃ layer resulted in a dramatic enhancement of the solar modulation ability (56.4%) and improvement of luminous transmittance (26.4%) when compared to single-layer VO₂ coating. According to optical measurements, the Cr₂O₃/VO₂ bilayer structure exhibits excellent optical performances with an enhanced solar modulation ability (ΔT_sol = 12.2%) and a high luminous transmittance (T_lum,lt = 46.0%), which makes a good balance between ΔT_sol and T_lum for smart windows applications. As for UV-shielding properties, more than 95.8% UV radiation (250-400 nm) can be blocked out by the Cr₂O₃/VO₂ structure. In addition, the visualized energy-efficient effect was modeled by heating a beaker of water using infrared imaging method with/without a Cr₂O₃/VO₂ coating glass.