Thermal studies on chemical bath deposited thermochromic VO2 thin film for energy efficient glass windows (original) (raw)
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Synthesis and characterization of VO2-based thermochromic thin films for energy-efficient windows
Nanoscale Research Letters, 2011
Thermochromic VO 2 thin films have successfully been grown on SiO 2-coated float glass by reactive DC and pulsed-DC magnetron sputtering. The influence of substitutional doping of V by higher valence cations, such as W, Mo, and Nb, and respective contents on the crystal structure of VO 2 is evaluated. Moreover, the effectiveness of each dopant element on the reduction of the intrinsic transition temperature and infrared modulation efficiency of VO 2 is discussed. In summary, all the dopant elements-regardless of the concentration, within the studied rangeformed a solid solution with VO 2 , which was the only compound observed by X-ray diffractometry. Nb showed a clear detrimental effect on the crystal structure of VO 2. The undoped films presented a marked thermochromic behavior, specially the one prepared by pulsed-DC sputtering. The dopants effectively decreased the transition of VO 2 to the proximity of room temperature. However, the IR modulation efficiency is markedly affected as a consequence of the increased metallic character of the semiconducting phase. Tungsten proved to be the most effective element on the reduction of the semiconducting-metal transition temperature, while Mo and Nb showed similar results with the latter being detrimental to the thermochromism.
ACS Omega, 2017
Monoclinic vanadium(IV) oxide (VO 2) has been widely studied for energy-efficient glazing applications because of its thermochromic properties, displaying a large change in transmission of near-IR wavelengths between the hot and cold states. The optimization of the reaction between VCl 4 and ethyl acetate via atmospheric-pressure chemical vapor deposition (APCVD) was shown to produce thin films of monoclinic VO 2 with excellent thermochromic properties (ΔT sol = 12%). The tailoring of the thermochromic and visible light transmission was shown to be possible by altering the density and morphology of the deposited films. The films were characterized by X-ray diffraction, atomic-force microscopy, scanning electron microscopy, ellipsometry, and UV−vis spectrometry. This article provides useful design rules for the synthesis of high-quality VO 2 thin films by APCVD.
Thermochromic VO2 films for energy-efficient windows
Solar Energy Materials, 1987
VO 2 films were produced by reactive e-beam evaporation followed by annealing post-treatment. Electrical measurements demonstrated a semiconductor-metal transition at % -60 o C. Spectrophotometry showed that the near-infrared solar transmittance was reduced when % was exceeded while the luminous transmittance remained relatively unchanged. This thermochromism may be utilized for regulating the energy throughput of windows. Practical application hinges on improved transmittance and on re-depression. These goals can be accomplished to some extent by dielectric overlayers, as verified by measurements on SiO2-coated VO 2 films.
Thin Solid Films, 2013
A simple and cost effective sol-gel process for producing vanadium dioxide thin films was developed via thermolysis of V 2 O 5 ·nH 2 O (n≈ 2) V V precursors prepared by dissolving vanadium powder or V 2 O 5 powder in 30% hydrogen peroxide solutions. After spin-coating on fused silica substrates and annealing at 750°C in vacuum, without any intermediate gas reducing step, the major phase VO 2 (M, monoclinic phase) was found in both of the films based on V-H 2 O 2 and V 2 O 5 -H 2 O 2 precursor, exhibiting large transmittance changes (>40%) in the IR region (>2000 nm) and small hysteresis loop width (b 5°C) which were comparable to reported epitaxial VO 2 films. The two films have similar metal-to-insulator transition temperature τ C =62.5°C, lower than the classical value of 68°C for VO 2 thin films. In addition, the method enables simple doping, as found for 0.56 at.% W-doped VO 2 films. This intrinsically simple solution process followed by one-step annealing makes it potentially useful in smart window applications.
Thermochromic vanadium oxide thin films: Electronic and optical properties
Journal of Physics: Conference Series
Vanadium dioxide, VO 2 , is a widely studied thermochromic material with potential applications in energy efficient window technology. It undergoes a first-order metal-toinsulator transition, accompanied by a crystal structure transformation from monoclinic to tetragonal rutile, at a critical temperature of 68 o C. Below this temperature, VO 2 is semiconducting and infrared transmitting whereas it is metallic and infrared reflecting above the transition temperature. However, in order to achieve significant thermochromic switching, the luminous transmittance of thin films will typically be less than 50%. Here we report on recent research to improve the luminous transmittance as well as the transmittance change at the transition temperature. We systematically evaluate the effect of antireflection coatings, doping with Mg and the performance of coatings comprising thermochromic nanoparticles in a transparent matrix. The last option is shown to give the best performance and holds great promise for practical applications.
Scientific Reports
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-...
Journal of Materials Chemistry, 2005
Atmospheric pressure chemical vapour deposition of V 22x M x O 2 (M = Mo, Nb; X = 0.01-0.003) thin films was achieved on glass substrates from the reaction of VOCl 3 , H 2 O and MCl 5 . Comparable reactions with SnCl 4 formed SnO 2 : VO 2 composites. The ease with which solid solutions or composite films formed was related to the relative reaction rates. The films were characterised by X-ray diffraction, Raman, X-ray photoelectron spectroscopy and scanning electron microscopy. Doping of the VO 2 phase was shown to affect both the growth morphology and the thermochromic properties of the films. The Mo-doped VO 2 films showed a thermochromic switch of 47 uC with a narrow hysteresis (4-6 uC).
Materials
Vanadium dioxide (VO2) with an insulator-to-metal (IMT) transition (∼68 °C) is considered a very attractive thermochromic material for smart window applications. Indeed, tailoring and understanding the thermochromic and surface properties at lower temperatures can enable room-temperature applications. The effect of W doping on the thermochromic, surface, and nanostructure properties of VO2 thin film was investigated in the present proof. W-doped VO2 thin films with different W contents were deposited by pulsed laser deposition (PLD) using V/W (+O2) and V2O5/W multilayers. Rapid thermal annealing at 400–450 °C under oxygen flow was performed to crystallize the as-deposited films. The thermochromic, surface chemistry, structural, and morphological properties of the thin films obtained were investigated. The results showed that the V5+ was more surface sensitive and W distribution was homogeneous in all samples. Moreover, the V2O5 acted as a W diffusion barrier during the annealing sta...
The Effect of Alkali Metal (Na, K) Doping on Thermochromic Properties of VO 2 Films
This work reports the synthesis of undoped and alkali metal doped thermochromic vanadium dioxide thin films by sol-gel spin coating and subsequent low-temperature annealing at 450 °C in N 2-H 2 atmosphere. The effect of sodium and potassium on the phase transition temperature as well as on the solar modulations were investigated. A dopant concentration of 0.3 at% resulted in a reduction of the critical transition temperature (T c) from 62 °C to 57 °C and 47 °C for the sodium and potassium doped films, respectively. Moreover, both dopants improved the solar modulations (ΔT sol) of the undoped VO 2 films from 3.81 to 9.44 and 5.43 %, respectively.