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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)


  • 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.


  • 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.


  • 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.


  • 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.


  • 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.


  • 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.


  • 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.


  • 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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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]....


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