Study of electrochromic cells incorporating WO, MoO, WO-MoO and VO coatings (original) (raw)
Related papers
Preparation and characterization of WO3-based electrochromic cell system
Chemical Vapor Deposition (CVD) technique has been used for fabrication of tungsten oxide (W03) films. An electrochromic device (ECD), using CVD-W03 as an electrochromic electrode has been prepared in combination with ion conductive polymer thin films, properly charged with H+ or tr, by using H3P04 or LiCI04. Optical modulation of about 50% at 600 nm in transmittance mode and time response of30 sec. are obtained.
Advanced electrochromic devices based on WO 3 thin films
Electrochimica Acta, 2001
We present work on the development of advanced materials suitable for use as electrochromic thin films (EC), ion storage layers and transparent conductors (TC) in electrochromic devices. These thin film layers were prepared in our laboratory by thermal evaporation and electron gun deposition. They were incorporated into electrochromic devices, which were subsequently characterized by optical and electrochemical techniques such as transmission spectroscopy, cyclic voltammetry and galvanostatic intermittent titration. WO 3 films 300-600 nm thick have been used as EC layers. They are amorphous and near-stoichiometric with a packing density of about 0.8. We have also developed textured WO 3 films. Their structure enhances Li + intercalation into the oxide matrix, thus doubling the diffusion coefficient. V 2 O 5 ion storage thin films were Li + doped both electrochemically and in vacuum leading to a 23% increase of the EC device coloration efficiency. We have fabricated electrochromic devices with ZnS/Ag/ZnS coatings as TCs. The use of multilayer ZnS/Ag/ZnS films was found to improve the electrical characteristics and to lower the emittance of the devices. All the devices described above can withstand more than 5000 coloration-bleaching cycles and have an open-circuit memory of several days. They are suitable for advanced glazing and other switching applications.
Recent research related to the development of electrochromic windows
Solar Energy Materials, 1986
The results of recent research on each of the layers of a solid-state multilayer structure for electrochromic windows are reviewed. This includes a review of the requirements of the multilayer structure for building windows and especially the need to have an electrochemically balanched system. The results indicate that excess free electron scattering in polycrystalline WO3 films (the electrochromatic layer) is not only the source of lower than desired reflectivity modulation, but it is also the major source of higher than desired absorptivity modulation. Research on LiA1F4 indicates that it is a viable candidate for the ion conducting layer, being a good lithium ion conductor and a good electronic insulator. Finally, we have recently discovered that tin-doped and undoped In203 films are mixed conductors, exhibiting lithium ion injection/extraction. This is significant since such films could possibly serve in the dual capacity of counterelectrode and transparent conductor, thereby reducing the complexity, the technical problems, and the cost of electrochromic window assemblies.
Journal of The Electrochemical Society, 2006
In this investigation, the effect of coloring voltage and thickness on optical and also electrochromical properties of WO 3 thin films has been studied. The WO 3 thin films were grown on glass and indium tin oxide coated conducting glass substrates by e-beam evaporation at different thicknesses of 200, 400, and 700 nm. Optical properties of the deposited samples were characterized in the ultraviolet-visible range ͑300-1100 nm͒. The optical bandgap energy of the WO 3 was obtained in a range of 3.3-3.5 eV showing its increase by decreasing the film thickness. The refractive index of the WO 3 films was measured around 2 in the visible range. Surface chemical states of the films were studied by X-ray photoelectron spectroscopy, which showed the stoichiometry of our deposited tungsten oxide thin films is acceptable. Atomic force microscopy was used for studying surface morphology of the deposited films. The electrochromic properties of the WO 3 films were characterized using a lithium-based electrolyte. It was shown that there is an optimum coloring voltage for each film thickness, which maximizes the change in optical density during electrochromic process. The coloration efficiency of the samples at the optimum voltage was linearly improved by increasing the film thickness at a constant wavelength ͑500 nm͒.
Journal of Physics D: Applied Physics, 2009
The colouration efficiency in the electrochromic devices depends upon the amount of intercalating charge in the tungsten oxide (WO 3−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 WO 3−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 WO 3 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 WO 3 thin films.
Characterisation and application of WO 3 films for electrochromic devices
Electron Technology Conference 2013, 2013
Electrochromic system is the one of the most popular devices using color memory effect under the influence of an applied voltage. The electrochromic system was produced based on the thin WO 3 electrochromic films. Films were prepared by RF magnetron sputtering from tungsten targets in a reactive Ar+O 2 gas atmosphere of various Ar/O 2 ratios. The technological gas mixture pressure was 3 Pa and process temperature 30 o C. Structural and optical properties of WO 3 films were investigated for as-deposited and heat treated samples at temperature range from 350 o C to 450 o C in air. The material revealed the dependence of properties on preparation conditions and on post-deposition heat treatment. Main parameters of thin WO 3 films: thickness d, refractive index n, extinction coefficient k and energy gap E g were determined and optimized for application in electrochromic system. The main components of the system were glass plate with transparent conducting oxides, electrolyte, and glass plate with transparent conducting oxides and WO 3 layer. The optical properties of the system were investigated when a voltage was applied across it. The electrochromic cell revealed the controllable transmittance depended on the operation voltage.
Comparative study of the electrochromic properties of WO3 thin films
Displays, 1988
This paper deals with a comparison between the electrochromic properties of tungsten oxide obtained by vacuum evaporation of WO 3 powder, anodic oxidation of W sheets and thermal oxidation of tungsten oxides obtained by chemical vapour deposited (CVD) onto SnO 2 substrate. Good electrochromic performances have been obtained with CVD layers despite their polycryst~llirte morphology and also with anodic oxidized W sheets despite the stoichiometry of the material. The results are compared with those obtained with amorphous tungsten oxide films prepared by vacuum evaporation. Moreover, we have shown that the electrochromic properties of the oxide (colouring efficiency, switching speed) depend on the nature of the substrate used. An AC complex impedance measurement was used to show the influence of this substrate on the behaviour of the electrical interfaces.
Electrochromism in tungsten oxide thin films prepared by chemical bath deposition
Journal of Electrochemical Science and Engineering, 2017
Tungsten oxide (WO3) thin films were prepared by a simple, economical, chemical bath deposition method onto fluorine doped tin oxide (FTO) coated glass substrates. The electrochemical properties of the films were characterized by cyclic voltammetry. The obtained films exhibited electrochromism, changing color from initially colorless to deep blue, and back to colorless. Visible transmittance spectra of (WO3) films were recorded insitu in their both, bleached and colored states. From those spectra, absorption coefficient () and the optical energy gaps were evaluated. The dependence of the optical density on the charge density was examined and the coloration efficiency () was calculated to be 22.11cm 2 C-1. The response times of the coloring and bleaching to an abrupt potential change from-2.5 V to +2.5 V and reverse, were found to be 9.3 and 1.2 s respectively. The maximum light intensity modulation ability of the films, when the AM1.5 spectrum is taken as an input, was calculated to be about 50 %.
Influence of Dopant Concentration on the Electrochromic Properties of Tungsten Oxide Thin Films
Electrochimica Acta, 2015
In order to achieve neutral coloration suitable for smart window applications WO 3 thin films modified by V 2 O 5 doping were deposited using RF magnetron sputtering method with 100 W RF power at room temperature (RT). The influence of dopant concentration on the structural and electrochromic performance have been investigated. Amorphous structure as revealed by the surface characteristics facilitates electrochromic process. Uniformly distributed channels between the aggregated grains provide shorter path ways to enhance coloration efficiency. PL emission presented higher photonic efficiency for 2% of V 2 O 5 doped WO 3 film. Reversible color change between transparent oxidized and deep blue colored reduced state depicted faster ion intercalation / deintercalation kinetics and faster switching responses with the bleaching time of 3.3 s and coloration time of 4.1 s. Better reversibility of 59.10 %, larger photopic contrast ratio of 2.29 and greater coloration efficiency of 66.75 cm 2 C-1 at 630 nm unveiled by 2% of V 2 O 5 doping, makes the film promising for practical applications.