Thermochromic VO2: Performance enhancement and application opportunities

Chromogenic materials offering variable optical properties as a function of an external stimulus are of obvious interest. Amongst these, thermochromic VO₂ has found uses in applications ranging from smart windows with a self-regulating solar transmittance to smart radiator devices for satellites with variable emissivity. The material itself nevertheless is plagued by multiple drawbacks such as: a high visible absorption, an unpleasant yellowish color, a high transition temperature, a low durability and a high deposition temperature. While some of these issues have been tackled some still remain.

Durability improvement: In the present work, we first demonstrate that HiPIMS-deposited VO₂ films display a higher durability to oxidation than their traditional RF-sputtered counterparts. Indeed, this increase is ascribed to the films higher density, compressive stress and, larger average grain size and thus lower amount of grain boundaries.

Low visible transmittance enhancement: We then demonstrate how by incorporating these VO₂ films into a low emissivity-type structure (dielectric|VO₂|Ag|dielectric), it is possible to decrease the VO₂’s thickness while still maintaining an appreciable solar transmittance variation vs. temperature and decreasing the undesirable visible absorption; the resulting filters also display low emissivity properties. All of the above characteristics are demonstrated through prototype samples and devices.