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Journal ArticleDOI

Electrochromic materials and devices for energy-efficient windows

01 Oct 1984-Solar Energy Materials (North-Holland)-Vol. 11, pp 1-27
TL;DR: In this article, inorganic and organic electrochromic materials are discussed in the context of developing a film-based optical shutter for a window application, which allows regulation of conductive and radiative heat transfer rates, with variable optical attenuation.
About: This article is published in Solar Energy Materials.The article was published on 1984-10-01 and is currently open access. It has received 548 citations till now. The article focuses on the topics: Electrochromism & Thin film.

Summary (3 min read)

1. INTRODUCTION

  • There is a wealth of technical literature and patents dealing with electrochromic materials and devices.
  • In the selection process many compounds and device configurations have undoubtably been rejected or ignored.
  • Historically, many promising technologies for electronic display purposes have yielded to select favored technologies.
  • Energy management and favorable use (or rejection) of incident solar radiation for heating and lighting can reduce net energy consumption.
  • An ideal optical shutter might be one that responds automatically to a changing ambient environment to provide comfort, visual needs, and energy savings.

3. CLASSES OF ELECTROCHROMIC MATERIALS

  • There are three general classes of electrochromic materials: (1) transition-metal oxides (primarily hydrous), (2) organic, and (3) intercalated materials.
  • Other important categories are organic compounds and intercalated materials.
  • For the organic groups, the viologen, pyrazoline, lanthanide phthalocyanine, anthraquinoide groups, and c.onductive organic polymers exhibit electrochromism.
  • 5,7-9 Table 1 covers selected inorganic compounds from which devices have been fabricated using solid electrolytes.
  • 30-31,69 Both Poly-VSA and Poly-SSA suffer from yellowing with time.

4. CATHODIC INORGANIC ELECTROCHROMICS

  • Both stoichiometric and sub-stoichiometric forms of some of the group VIB oxides such as W0 3 and Mo03' along wi th various admixtures, exhibit electrochromism.
  • The general concern, in terms of deposited microstructure, is the material's ability to easily transport protons or ions.
  • 74 Incorporation of water appears to dictate electrochromic -6-10' coloration speed.
  • 75 Anodically-prepared films are generally much faster than others deposited by alternate techniques.
  • 77 Films formed by dry thermal oxidation in most oxide systems show poor electrochromism and require pretreatment to activate the material.

E. Titanium Oxide

  • Amorphous titanium oxide undergoes an electrochromic reaction after the following: S3 TiOOH.
  • After coloration, the bandgap moved to 2.99 eV and absorption edge decreased to 0.415 microns.
  • Within this class several materials exhibit coloration upon reduction.
  • Its long reaction time is a drawback, however.
  • PTA has also been used, exclusively as an electrochromic disp1ay.

G. Metal-oxide Cermets and Mixed Oxide Composites

  • Au-W0 3 cermets and Pt-W0 3 cermets have been formulated as e1ectrochromic materials.
  • Au and Pt were added in the hope "tuning" the color of the electrochromic material.
  • The characteristics of 20-120 angstrom diameter gold particles in amorphous W0 3 produce a material that is blue initially and becomes red or pink when electrochromica11y excited.

5. ANODIC INORGANIC ELECTROCHROMICS

  • The hydrous oxides in group VIII, the platinum group, have been investigated for electrochromism.
  • 7 ,47 They color by anodic transfer of elec trons out of the film coupled with cation ejection or anion injection from the electrolyte.
  • Also, .iridium can be vacuum evaporated on conductive glass and subsequently anodized to make an oxide film.
  • The structure and exact composition of these films is still unknown.
  • The structure of SIROF films is identified as densely amorphous, while AIROF's have highly porous crystalline or amorphous structures.

6. ORGANIC ELECTROCHROMIC MATERIALS

  • A number of organic materials can exhibit electrochromism.
  • Organmetallics, such as phthalocyanines of lanthanides and poly tungsten anions, have also been researched.
  • The basic organic electrochromic reactions have been listed by type: type 1, a simple redox reaction, which gives a colored species; type 2, also a redox reac tion but coupled wi th an independent reaction resulting in variable color persistence; and type 3, a redox reaction with a chemical reaction producing an insoluble colored species, which affords a memory effect.
  • This type is not well suited for a window shutter.
  • Reverse leakage current exists, and leakage paths should be eliminated for long-term coloration.

• A. Viologens

  • Viologens are commonly used for oxidation-reduction indicators.
  • The optical density of the resulting colored product peaks at 545 nm and has an absorption coefficient of a = 26000/cm. 60 The reaction is reversed by reversing the current or shorting electrodes, the latter being slower.
  • Since an oxidation-reduction reaction is used, hermetic sealing of the device from the air is very important; this may be a drawback for a window shutter.
  • Also, benzyl viologen has been mixed with a polymerized viologen dibromide to make a two-color display.
  • A GaAs-viologen device has been fabricated using photo-electrochemical principles.

7. REDOX FERRIC FERROCYANIDE

  • Ferric ferrocyanide, known as Prussion blue exhibitsbicolor electrochromism and UV photochromism.
  • It exhibits three color states depending upon the conditions of oxidation and reduction.
  • It is of technical interest because the intercalated structure might be useful to synthesize new electrochromic materials.
  • Intercalation can be performed in phases where, at higher stages, fewer interlayer spaces are occupied by metallic compounds.
  • The writing and erase times are 0.2 sec; power consumption is equivalent to other electrochromic devices.

DEVICE TECHNOLOGY

  • As noted before, elec trochromic opticalswi tching devices can use either a liquid or a solid electrolyte.
  • (There are many other configurations and device considerations embodied in these patents than covered here).
  • Generally, the electrochromic device operates between two eIsctrode layers.
  • These can be semi-transparent metals, such as 50-100 A of gold or transparent conductors, such as indium-tinoxide (ITO), doped tin oxide, or cadmium stannate.
  • There are only two general types of solid-state devices, one dependent on and one independent of the presence of water.

In this

  • Up to now, anodic and cathodic electrochromic layers were discussed separately.
  • Cells can rely on the transport of Li+,Na+, or Ag+ cations.
  • Due to the ionic size and slow solid-state diffusion rates, these devices use fast-ion-conductors to decrease switching time.
  • Temperature response is another consideration for using electrochromics as window shutters.
  • In practice, for display devices, a graphite electrode, graphite paper, or another electrochromic is used.

8. SUMMARY AND CONCLUSIONS

  • This paper has decribed the state of the art in electrochromic material and device design.
  • Certainly the RyWO x systems are the most researched; by replacing hydrogen with an alkali metal element, coloration can also be al tered.
  • Critical materials research issues for transmitting electrochromic devices are: 1) understanding the electrochromic phenomena and its relationship to interfaces, microstructure and chemistry of thin films, 2) determination of the solar optical properties and the range of properties for several materials, 3) development of transparent proton or ion storing counter-electrodes, 4) development of simplified device structures.
  • Issues of performance of optical shutter materials include: reasonable switching time, optical density range, optical homogeneity, spectral characteristics, and long cyclic lifetime.
  • For many of the materials described here, insufficient information is available to address these considerations properly.

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Citations
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Journal ArticleDOI
TL;DR: In this paper, the authors reviewed work on In2O3:Sn films prepared by reactive e−beam evaporation of In2 O3 with up to 9 mol'% SnO2 onto heated glass.
Abstract: We review work on In2O3:Sn films prepared by reactive e‐beam evaporation of In2O3 with up to 9 mol % SnO2 onto heated glass. These films have excellent spectrally selective properties when the deposition rate is ∼0.2 nm/s, the substrate temperature is ≳150 °C, and the oxygen pressure is ∼5×10−4 Torr. Optimized coatings have crystallite dimensions ≳50 nm and a C‐type rare‐earth oxide structure. We cover electromagnetic properties as recorded by spectrophotometry in the 0.2–50‐μm range, by X‐band microwave reflectance, and by dc electrical measurements. Hall‐effect data are included. An increase of the Sn content is shown to have several important effects: the semiconductor band gap is shifted towards the ultraviolet, the luminous transmittance remains high, the infrared reflectance increases to a high value beyond a certain wavelength which shifts towards the visible, phonon‐induced infrared absorption bands vanish, the microwave reflectance goes up, and the dc resisitivity drops to ∼2×10−4 Ω cm. The corre...

2,124 citations

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TL;DR: In this paper, the preparation of a colloidal colloidal by un procede sol gel is described, and a procedure for determination des proprietes electriques et electrochimiques is described.

2,040 citations

Journal ArticleDOI
TL;DR: The Robust Envelope Construction Details for Buildings of the 21st Century (ROBUST) project as mentioned in this paper was supported by the Research Council of Norway, AF Gruppen, Glava, Hunton Fiber as, Icopal, Isola, Jackon, maxit, Moelven ByggModul, Ramboll, Skanska, Statsbygg and Takprodusentenes forskningsgruppe through the SINTEF/NTNU research project.

1,127 citations


Cites background from "Electrochromic materials and device..."

  • ...[78] C.M. Lampert, Large-area smart glass and integrated photovoltaics, Solar Energy Materials and Solar Cells 76 (2003) 489–499....

    [...]

  • ...[75] C.M. Lampert, T.R. Omstead, P.C. Yu, Chemical and optical properties of electrochromic nickel oxide films, Solar Energy Materials 14 (1986) 161–174....

    [...]

  • ...[147] P.C. Yu, C.M. Lampert, In-situ spectroscopic studies of electrochromic hydrated nickel oxide films, Solar Energy Materials 19 (1989) 1–16....

    [...]

  • ...A lifetime of 105 cycles and 30 years has been expressed within the range of 30 to 60 1C by SAGE, which conforms the desired properties by Lampert [76]....

    [...]

  • ...Requirements and expectations The required properties for smart windows for solar and energy applications have been expressed by Lampert [76] (see Table 5) and surveys have recently been performed [128–132] of Table 5 Requirements for electrochromic windows in the bleached (bl.) and coloured (col.) state [76]....

    [...]

Journal ArticleDOI
TL;DR: In this article, the authors discuss the next generation of smart windows based on organic materials which can change their properties by reflecting or transmitting excess solar energy (infrared radiation) in such a way that comfortable indoor temperatures can be maintained throughout the year.
Abstract: Windows are vital elements in the built environment that have a large impact on the energy consumption in indoor spaces, affecting heating and cooling and artificial lighting requirements. Moreover, they play an important role in sustaining human health and well-being. In this review, we discuss the next generation of smart windows based on organic materials which can change their properties by reflecting or transmitting excess solar energy (infrared radiation) in such a way that comfortable indoor temperatures can be maintained throughout the year. Moreover, we place emphasis on windows that maintain transparency in the visible region so that additional energy is not required to retain natural illumination. We discuss a number of ways to fabricate windows which remain as permanent infrared control elements throughout the year as well as windows which can alter transmission properties in presence of external stimuli like electric fields, temperature and incident light intensity. We also show the potential impact of these windows on energy saving in different climate conditions.

877 citations

Journal ArticleDOI
TL;DR: In this article, the authors present a detailed review of the state-of-the-art for electrochromics and its applications in smart windows and provide ample references to current literature of particular relevance.

801 citations

References
More filters
Journal ArticleDOI
Philip W. Anderson1
TL;DR: In this article, a simple model for spin diffusion or conduction in the "impurity band" is presented, which involves transport in a lattice which is in some sense random, and in them diffusion is expected to take place via quantum jumps between localized sites.
Abstract: This paper presents a simple model for such processes as spin diffusion or conduction in the "impurity band." These processes involve transport in a lattice which is in some sense random, and in them diffusion is expected to take place via quantum jumps between localized sites. In this simple model the essential randomness is introduced by requiring the energy to vary randomly from site to site. It is shown that at low enough densities no diffusion at all can take place, and the criteria for transport to occur are given.

9,647 citations

Journal ArticleDOI
TL;DR: In this paper, the optical absorption spectra of amorphous and crystalline thin Wo3 films have been measured in the temperature range 110° to 500°K and the temperature coefficient of the band edges was found to be − 5.0 × 10−4 eV/°K.
Abstract: Thin films of Wo3 deposited on quartz substrates at room temperature have been shown to be amorphous in structure. The optical absorption spectra of the amorphous and crystalline films have been measured in the temperature range 110° to 500°K. The fundamental absorption edge of an amorphous film occurs at 3800 A which on crystallization moves to 4500 A. On the high-energy side of the absorption edge several absorption peaks are resolvable in both types of film. The frequency dependence of the absorption coefficient below 104 cm−1 is described by an expression of the form K (v, T) = K 0 exp[− (β/kT) (E 0 − hv)] and above 104 cm−1 it follows a square law dependency. The temperature coefficient of the band edges was found to be − 5.0 × 10−4 eV/°K and the estimated band gaps at 0°K were found to be 3.65 and 3.27 eV for the amorphous and crystalline films, respectively. The electrical conductivity of a thin film has been measured in the temperature range 298–573°K and the activation energy was found t...

933 citations

Journal ArticleDOI
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.

344 citations

Journal ArticleDOI
TL;DR: In this article, an x-ray photoelectron and optical investigation of three thin-film transition metal oxides, namely, WO3, MoO3 and V2O5 are reported.
Abstract: Qualitative results of an x‐ray photoelectron and optical investigation of three thin‐film transition‐metal oxides, namely, WO3, MoO3, and V2O5 are reported. Data were obtained on films that were not colored and colored by an electrochromic process. The particular electrochromic coloration process used is electrolytic in nature and employs a sandwich‐structure electrochromic cell and electrolyte pool. The optical spectra show increased absorption in the visible (red) and near‐infrared spectral regions upon coloration. The photoelectron spectra for colored films exhibit a small band near the Fermi level and asymmetric band shapes for metal core‐level bands which are absent in films that are not colored. The new band and the asymmetric band shapes are attributed to the presence of a reduced‐state species caused by the presence of trapped electrons and metal bronze formation. Results from coloration with different electrolyte pools, i.e., H+, Li+, Na+, K+, Cs+, and Mg2+ electrolytes, are reported.

337 citations