Studies on the correlation between electrochromic colouration and the relative density of tungsten trioxide (WO3−x) thin films prepared by electron beam evaporation
TL;DR: In this paper, the dependence of intercalated charge in WO3−x thin films on the film density is reported, and an intercalating charge of 59, 48 and 39 cmC cm−2 brings about a change of 0.24, 0.16 and 0.13
Abstract: The colouration efficiency in the electrochromic devices depends upon the amount of intercalating charge in the tungsten oxide (WO3−x) thin films. One of the physical properties of the film that significantly influence the intercalating charge is the film density. In this paper, the dependence of intercalated charge in WO3−x thin films on the film density is reported. The amorphous tungsten oxide thin films have been prepared by electron beam evaporation at three substrate temperatures: 300, 470 and 570 K. With increasing substrate temperature, the refractive indices of the films increase. The relative film density calculated from the refractive index using the Lorentz–Lorentz relationship increases with the substrate temperature. With increasing density of the WO3 thin films, the diffusion coefficients of protons and the amount of intercalated charge decrease. The intercalated charge in the coloured electrochromic thin films brings about a change in the surface work function of the thin film; the difference in the surface work function (between the coloured and the bleached states) is measured by the Kelvin probe. In the present investigation, an intercalating charge of 59, 48 and 39 mC cm−2 brings about a change of 0.24, 0.16 and 0.13 eV in the surface work function of the WO3 thin films.
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TL;DR: The first demonstration of a unique self-recovery of capacity in transition metal oxide anode materials in Li-ion batteries is presented by reducing tungsten trioxide (WO3) via the incorporation of urea, followed by annealing in a nitrogen environment.
Abstract: It has been a challenge to use transition metal oxides as anode materials in Li-ion batteries due to their low electronic conductivity, poor rate capability and large volume change during charge/discharge processes. Here, we present the first demonstration of a unique self-recovery of capacity in transition metal oxide anodes. This was achieved by reducing tungsten trioxide (WO3) via the incorporation of urea, followed by annealing in a nitrogen environment. The reduced WO3 successfully self-retained the Li-ion cell capacity after undergoing a sharp decrease upon cycling. Significantly, the reduced WO3 also exhibited excellent rate capability. The reduced WO3 exhibited an interesting cycling phenomenon where the capacity was significantly self-recovered after an initial sharp decrease. The quick self-recoveries of 193.21%, 179.19% and 166.38% for the reduced WO3 were observed at the 15th (521.59/457.41 mA h g−1), 36th (538.49/536.61 mA h g−1) and 45th (555.39/555.39 mA h g−1) cycles respectively compared to their respective preceding discharge capacity. This unique self-recovery phenomenon can be attributed to the lithium plating and conversion reaction which might be due to the activation of oxygen vacancies that act as defects which make the WO3 electrode more electrochemically reactive with cycling. The reduced WO3 exhibited a superior electrochemical performance with 959.1/638.9 mA h g−1 (1st cycle) and 558.68/550.23 mA h g−1 (100th cycle) vs. pristine WO3 with 670.16/403.79 mA h g−1 (1st cycle) and 236.53/234.39 mA h g−1 (100th cycle) at a current density of 100 mA g−1.
80 citations
TL;DR: In this article, the effect of substrate temperature on the structural, morphological, optical and electrochromic properties of tungsten trioxide (WO 3 ) films was systematically studied.
Abstract: Thin films of tungsten trioxide (WO 3 ) have been prepared by RF reactive magnetron sputtering of tungsten target at different substrate temperatures in the range 303–673 K and at fixed oxygen partial pressure of 6×10 −2 Pa and sputter pressure of 4 Pa. The effect of substrate temperature on the structural, morphological, optical and electrochromic properties of WO 3 films was systematically studied. The films formed at 303 K were of X-ray amorphous, while those deposited at substrate temperatures ≥473 K were crystallized into orthorhombic phase WO 3 . The crystallite size of the films increased from 17 to 24 nm with increase of substrate temperature from 473 to 673 K. Raman studies confirmed that the presence of O–W–O and W=O bonds in WO 3 films. The surface morphology of the films was significantly varied with substrate temperature. The optical transmittance data revealed that the optical band gap increased from 3.08 to 3.48 eV and refractive index increased from 2.18 to 2.26 with increase of substrate temperature from 303 to 673 K respectively. The WO 3 films formed at substrate temperature of 473 K exhibited better optical transmittance modulation of 40% between colored and bleached state with a color efficiency of 33.8 cm 2 /C and diffusion coefficient of 1.85×10 −11 cm 2 /s.
62 citations
TL;DR: In this paper, the correlation between material properties and their effects on electrical stability of a-IGZO thin-film transistor (TFTs) was studied as a function of p d.
57 citations
TL;DR: In this article, the effect of porosity on the physical and electrochromic properties of WO3 was studied by radio frequency magnetron sputtering and the best performing films were combined into a 27 layer quarter-wave interference filter which is shown to cycle between bleached and colored states, while providing attractive transmission.
55 citations
TL;DR: WO3 thin films were prepared by surfactant mediated spray pyrolysis deposition on fluorine-doped tin oxide (FTO) conductive glass using hexadecylthymethylammonium bromide (HTAB) as structure-directing agent as discussed by the authors.
32 citations
References
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TL;DR: In this article, the progress that has taken place since 1993 with regard to film deposition, characterization by physical and chemical techniques, optical properties, as well as electrochromic device assembly and performance is reviewed.
1,304 citations
TL;DR: In this paper, the optical absorption of amorphous electrochromic display layers is explained as small polaron absorption and the necessary W5+5d −electron localization is favored by the lattice disorder.
Abstract: The optical absorption of amorphous electrochromic display layers is explained as small polaron absorption. The necessary W5+ 5d‐electron localization is favored by the lattice disorder. This is concluded from the change of the optical properties to free‐electron‐like behavior upon crystallization of the layers. The increased electrocoloration stability of amorphous layers and the blue shift of the absorption peak in Mo‐doped films can also be explained within the model given.
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263 citations
TL;DR: In this paper, the electrochromic mechanism in amorphous tungsten oxide films was studied using Raman scattering measurements, and the authors concluded that the as-deposited films contain mainly the W4+ and W6+ states and the W5+ states are generated as a result of reduction of the W6+) states when lithium or hydrogen ions and electrons are inserted.
Abstract: The electrochromic mechanism in amorphous tungsten oxide films is studied using Raman scattering measurements. The Raman spectra of as-deposited films show two strong peaks at 770 and 950 cm−1 due to vibrations of the W6+–O and W6+=O bonds, respectively, and a weaker peak at 220 cm−1 that we attribute to the W4+–O bonds. When lithium or hydrogen ions and electrons are inserted, extra Raman peaks due to W5+–O and W5+=O bonds appear at 330 and 450 cm−1, respectively. Comparison of the Raman spectra of sputtered isotopic a-W16O3−y and a-W18O3−y films confirms these assignments. We conclude that the as-deposited films contain mainly the W4+ and W6+ states, and the W5+ states are generated as a result of reduction of the W6+ states when lithium or hydrogen ions and electrons are inserted. We propose that the optical absorption in the colored films is caused by transitions between the W6+ and W5+, and W5+ and W4+ states.
207 citations
TL;DR: The physical and electrochemichromic properties of amorphous and crystalline tungsten oxide films prepared by thermal evaporation of WO3 powder under a reducing atmosphere have been investigated.
Abstract: The physical and electrochemichromic properties of the amorphous and crystalline tungsten oxide films prepared by thermal evaporation of WO3 powder under a reducing atmosphere have been investigated. The oxide films with 850–24 500 A thick were deposited on the substrates maintained at a temperature ranging from 50 to 500 °C under a vacuum below 1×10−5 Torr. Properties of the oxide films formed depend considerably on the deposition temperature. The as‐prepared oxide films formed at a temperature higher than 400 °C have a resistivity of 10−3−10 Ω cm, and are blue colored, and mainly composed of crystalline WO3. The oxide films formed at a temperature lower than 350 °C have a resistivity of 105–109 Ω cm, and are transparent and amorphous. Both of the amorphous and crystalline oxide films have good electrochemichromic properties. From x‐ray analysis, the crystalline WO3 thick films were found to change to hydrogen tungsten bronze films with a chemical composition of H0.33WO3 during electrochemical coloration...
110 citations