A low-temperature synthesis of strongly thermochromic VO2-based coatings for energy-saving smart windows

Result code in IS VaVaI

<a href="https://www.isvavai.cz/riv?ss=detail&h=RIV%2F49777513%3A23520%2F25%3A43976505" target="_blank" >RIV/49777513:23520/25:43976505 - isvavai.cz</a>

Result on the web

—

DOI - Digital Object Identifier

—

Result language

angličtina

Original language name

A low-temperature synthesis of strongly thermochromic VO2-based coatings for energy-saving smart windows

Original language description

Vanadium dioxide (VO2) exhibits a reversible phase transition from a low-temperature monoclinic VO2 (M1) semiconducting phase to a high-temperature tetragonal VO2 (R) metallic phase at a transition temperature of approximately 68 °C for the bulk material. The automatic response to temperature and the abrupt decrease of infrared transmittance with almost the same luminous transmittance in the metallic state make VO2-based coatings a promising candidate for thermochromic smart windows reducing the energy consumption of buildings. To meet the requirements for large-scale implementation on building glass, VO2-based coatings should satisfy the following strict criteria simultaneously: a deposition temperature close to 300 °C, a transition temperature close to 25 °C, an integral luminous transmittance Tlum &gt; 60 %, a modulation of the solar energy transmittance ΔTsol &gt; 10 %, long-term environmental stability, and a more appealing color than yellowish or brownish colors in transmission.The paper deals with strongly thermochromic YSZ/W and Sr co-doped VO2/SiO2 coatings, where YSZ is Y-stabilized ZrO2, prepared using a scalable sputter deposition technique on standard soda-lime 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 Tlum = 63.7% (below the transition temperature) and 60.7% (above the transition temperature) and a modulation of the solar energy transmittance ΔTsol = 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 yet been reported in the literature.The fundamental principles of this technique, and the design, structure and optical properties of the thermochromic coatings are presented. Reactive high-power impulse magnetron sputtering with a pulsed O2 flow feedback control allowed us to prepare crystalline VO2 of the correct stoichiometry at a low deposition temperature. The W doping of VO2 decreases the transition temperature to room temperature, while the Sr doping of VO2 results in a significant increase in Tlum. An original design of a three-layer VO2-based coating utilizing a second-order interference in two antireflection layers is used to maximize Tlum and ΔTsol simultaneously. A compact crystalline structure of the bottom YSZ antireflection layer further improves the VO2 crystalline layer, while the top SiO2 antireflection layer provides also mechanical and environmental protection for the thermochromic VO2-based layer.

Czech name

—

Czech description

—

Type

O - Miscellaneous

CEP classification

—

OECD FORD branch

20506 - Coating and films

Project

—

Continuities

S - Specificky vyzkum na vysokych skolach

Publication year

2025

Confidentiality

S - Úplné a pravdivé údaje o projektu nepodléhají ochraně podle zvláštních právních předpisů