Dataset Information

Bio-inspired TiO₂ nano-cone antireflection layer for the optical performance improvement of VO₂ thermochromic smart windows.

ABSTRACT: Vanadium dioxide (VO₂) is a promising material for thermochromic glazing. However, VO₂ thermochromic smart windows suffer from several problems that prevent commercialization: low luminous transmittance (T_lum) and low solar modulation ability (?T_sol). The solution to these problems can be sought from nature where the evolution of various species has enabled them to survive. Investigations into the morphology of moths eyes has shown that their unique nanostructures provide an excellent antireflection optical layer that helps moths sharply capture the light in each wavelength from a wide angle. Inspired by this mechanism, a VO₂ thermochromic smart window coated with a TiO₂ antireflection layer with a novel nano-cone structure, is presented in this study to achieve high T_lum and ?T_sol. Optimization for the key structure parameters is summarized based on the FDTD numerical simulations. The optimized structure exhibits a T_lum of 55.4% with ?T_sol of 11.3%, an improvement of about 39% and 72% respectively compared to the VO₂ window without an antireflection layer. Furthermore, wide-angle antireflection and polarization independence are also demonstrated by this nano-cone coating. This work provides an alternative method to enhance the optical performance of VO₂ smart windows.

SUBMITTER: Liu S

PROVIDER: S-EPMC7347835 | biostudies-literature | 2020 Jul

REPOSITORIES: biostudies-literature

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Bio-inspired TiO2 nano-cone antireflection layer for the optical performance improvement of VO2 thermochromic smart windows.

Liu Sai S Tso Chi Yan CY Lee Hau Him HH Zhang Yi Y Yu Kin Man KM Chao Christopher Y H CYH

Scientific reports 20200709 1

Vanadium dioxide (VO2) is a promising material for thermochromic glazing. However, VO2 thermochromic smart windows suffer from several problems that prevent commercialization: low luminous transmittance (Tlum) and low solar modulation ability (ΔTsol). The solution to these problems can be sought from nature where the evolution of various species has enabled them to survive. Investigations into the morphology of moths eyes has shown that their unique na ...[more]

PMID: 32647345

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Project description:Over the years, vanadium dioxide, (VO2(M1)), has been extensively utilised to fabricate thermochromic thin films with the focus on using external stimuli, such as heat, to modulate the visible through near-infrared transmittance for energy efficiency of buildings and indoor comfort. It is thus valuable to extend the study of thermochromic materials into the mid-infrared (MIR) wavelengths for applications such as smart radiative devices. On top of this, there are numerous challenges with synthesising pure VO2 (M1) thin films, as most fabrication techniques require the post-annealing of a deposited thin film to convert amorphous VO2 into a crystalline phase. Here, we present a direct method to fabricate thicker VO2(M1) thin films onto hot silica substrates (at substrate temperatures of 400 °C and 700 °C) from vanadium pentoxide (V2O5) precursor material. A high repetition rate (10 kHz) femtosecond laser is used to deposit the V2O5 leading to the formation of VO2 (M1) without any post-annealing steps. Surface morphology, structural properties, and UV-visible optical properties, including optical band gap and complex refractive index, as a function of the substrate temperature, were studied and reported below. The transmission electron microscopic (TEM) and X-ray diffraction studies confirm that VO2 (M1) thin films deposited at 700 °C are dominated by a highly texturized polycrystalline monoclinic crystalline structure. The thermochromic characteristics in the mid-infrared (MIR) at a wavelength range of 2.5-5.0 μm are presented using temperature-dependent transmittance measurements. The first-order phase transition from metal-to-semiconductor and the hysteresis bandwidth of the transition were confirmed to be 64.4 °C and 12.6 °C respectively, for a sample fabricated at 700 °C. Thermo-optical emissivity properties indicate that these VO2 (M1) thin films fabricated with femtosecond laser deposition have strong potential for both radiative thermal management or control via active energy-saving windows for buildings, and satellites and spacecraft.

Dataset Information

Bio-inspired TiO₂ nano-cone antireflection layer for the optical performance improvement of VO₂ thermochromic smart windows.

Publications

Bio-inspired TiO<sub>2</sub> nano-cone antireflection layer for the optical performance improvement of VO<sub>2</sub> thermochromic smart windows.

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