Thermochromic VO₂‐based multilayer films with enhanced luminous transmittance and solar modulation

Abstract

Vanadium dioxide (VO 2 ) shows an abrupt and reversible change in optical and electrical properties when the temperature is raised beyond a critical point of ∼68 • C. Films made from this material have a potential to be used in energy efficient "smart" windows with temperature-dependent throughput of solar radiation. Two of the drawbacks of this material have been its low luminous transmittance and limited solar modulation of transmittance during switching. In this work we report calculations and experiments on multilayers of VO 2 and TiO 2 , produced by reactive DC magnetron sputtering, that significantly improve the luminous transmittance and solar modulation of the films during switching. We also explore the angular-dependent transmittance of five-layer TiO 2 /VO 2 /TiO 2 /VO 2 /TiO 2 films and demonstrate that the modulation of luminous and solar transmittance can be enhanced at non-normal angles of incidence.

Thermochromic VO2 nanorods made by sputter deposition: Growth conditions and optical modeling

“…Figure 9 shows the real and imaginary parts of ε VO2 (λ) and compares our results with those earlier reported in the literature. [138][139][140][141][142] Clearly the agreement among the data is satisfactory.…”

Durability of thermochromic VO2 thin films under heating and humidity: Effect of Al oxide top coatings

“…It should be noted that such coatings may be desired not only for oxidation protection but for their optical functionality. Thus the top coating can provide anti-reflection and thereby enhance the luminous transmittance, which is advantageous for windows-related applications [11,16], and studies have been reported for anti-reflecting layers based on oxides of Si [32][33][34][35][36][37], Ti [36][37][38][39][40][41][42], Zr [43] and Al [37]. It is likely that some or all of these oxide layers are able to impart oxidation protection of the underlying VO 2 .…”

Thermochromic undoped and Mg-doped VO2 thin films and nanoparticles: Optical properties and performance limits for energy efficient windows

“…The overarching goal is to assess VO 2 -based materials for energy efficient fenestration, and the present paper is a sequel to earlier ones. [1][2][3][4][5][6][7][8][9][10] Vanadium dioxide is a well known thermochromic material. 11 It undergoes a first-order metal-to-insulator transition, accompanied by a crystal structure transformation from monoclinic (M 1 ) to tetragonal rutile, at a critical temperature τ c ≈ 68 °C.…”

“…[26][27][28][29] Furthermore, antireflection (AR) coatings are able to improve T lum and ΔT sol , and especially good properties have been reported for five-layer coatings of alternating TiO 2 and VO 2 . 2,3 Recent modeling studies on "nanothermochromics" 4,5 have shown that VO 2 nanoparticles can offer significantly higher values of T lum and ΔT sol than films, and these new possibilities have led to a burst of research on such nanoparticles. 6,9,19,22,25,[30][31][32][33][34] 25 This paper is outlined as follows: Section II reports on the samples and treats sputter deposition, compositional and structural data, and optical characterization and properties; this section also contains a discussion of sample quality which-as found in recent work of ours 9 -may be critically dependent on several aspects of the thin film preparation.…”