VO2 nanostripe-based thin film with optimized color and solar characteristics for smart windows

Abstract

This study presents a structuration approach to reach a high luminous transmittance (Tlum) and solar modulation efficiency (ΔTsol) of thermochromic vanadium dioxide (VO2) thin films. Before starting optical simulations, we confirm that the optical properties of monoclinic VO2 continuous films deposited by reactive magnetron sputtering show a good correspondence with numerical results. Then, calculations on ordered VO2 nanostripes demonstrate an enhanced transmittance due to the presence of vertical openings, leading to a variety of photonic effects. A series of optimizations by varying the column width, period, and film thickness establishes that 20 nm wide and 10 nm separated nanostripes have a ΔTsol of 14.2% and a Tlum of 47.6% for a film thickness of 250 nm. In comparison to a dense film without nanostructuring, the film transparency (related to Tlum) is significantly enhanced, while ΔTsol remains unchanged. Furthermore, this also translates into a favorable, less opaque color, so the geometry could be useful for various thermochromic applications, such as smart windows.

Controlling the crystalline orientation and textual morphologies of the VO2 film and the effect on insulator–metal transition properties

“…15) Although the MIT property of VO 2 films cannot compare with that of single-crystals, they can stand many reversible SPT cycles, so VO 2 films are widely investigated as the functional materials in electrical switches, smart windows, storage devices, uncooled microbolometers, and thermal diodes. [16][17][18][19][20] The performances of VO 2 films rely on their MIT features, which were found to relate to defects, grain sizes, boundaries, and textured morphologies. [21][22][23][24] Our recent study showed that crystalline orientations might have an apparent effect on the MIT of the VO 2 films over quartz glasses, obtained from a controllable thermal oxidation of V-riched films in a vacuum.…”

Thermochromic Energy Efficient Windows: Fundamentals, Recent Advances, and Perspectives

“…Nano/microstructured engineering surfaces, with either rigid or irregular structures, can wavelength-sensitively interact with incident photons to regulate their electromagnetic field distribution at the surface or interfaces, resulting in drastic differences from conventional planar coating surfaces. − For VO 2 -based energy-efficient windows, various specially designed structures at the nano- and microscales have been developed, to suppress the surface reflection, , enhance the luminous transmittance and solar energy modulation ability, ,, optimize color, , and regulate the localized surface plasma. , …”

“…A summary of thermochromic performance for VO 2 film with multilayer structures is shown in Table 3. For VO 2 -based energy-efficient windows, various specially designed structures at the nano-and microscales have been developed, to suppress the surface reflection, 213,214 enhance the luminous transmittance and solar energy modulation ability, 212,215,216 optimize color, 217,218 and regulate the localized surface plasma. 219,220 Long et al explored three different types of nanogrid structures with square holes, circular holes, and circular holes in a hexagonal arrangement to optimize the optical properties by a 3D finite-difference time-domain (FDTD) method.…”

Facile Fabrication of High-Performance Thermochromic VO2-Based Films on Si for Application in Phase-Change Devices

“…Driven by structural changes from insulating monoclinic (M) at low temperature to metallic rutile (R) at temperatures above the transition temperature ( T c ), this phenomenon involves great optical and electronic changes. This makes this material especially advantageous for thermochromic smart window applications. − These appealing properties of VO 2 have also been exploited for a wide range of photonic, optoelectronic, and electronic phase-change devices on silicon platforms, such as optical modulators and limiters, − infrared (IR) photodetectors, , or optical , and electrical − switches. Likewise, the VO 2 /Si system is also considered a potential candidate for its application as a passive intelligent radiator for spacecraft thermal control .…”