Electrochromic element

Interest has developed in electrochromic light transmission modulators, which are called smart windows , for control of temperature and lighting in buildings and automobiles. A cross section of an electrochromic light transmission modulator is shown in Fig. 11.31 (Rauh and Cogan, 1988). The two electrochromic elements of the structure are designated ECl and EC2, and are sandwiched between two thin film, optically transparent, electrodes of ITO and separated by an electrolyte. The ECl layer should colour when a negative potential is applied and the EC2 layer should either colour under positive potentials or remain in a transparent state. This is indicated by the chemical reactions ... 

QDO, PDO, and related compounds are the subject of a great number of invention patents, particularly for its uses in material sciences. For example, QDOs were included in the formulation of modified unsaturated polymers and rubbers [174,175]. Polymers with a QDO substructure as monomeric unit were used to produce fibers, films, electrochromic elements, electrodes, semiconductors, and electrolyte solutions for secondary batteries [176-179]. 

While with photochromic solids, light is used to cause colour change and detect it, with electrochromic solids, an electric field is used to change colour. Certain hemiquinones whose colour is externally switchable by an electric field are potentially useful as memory elements. 

Fuel cell polymer battery photoelectric cell capacitor Storage element liquid crystal display device electrochromic display device electrochemiluminescence device photoelectric transducer Biosensor ion sensor detector in HPLC and FIA gas sensor voltam-metric indicator electrode reference electrode... 

There is growing evidence of developing high-technology uses of pyridines, particularly as quaternary salts, as components of electrolytic capacitors, photocondnctors. rechargeable batteries, complex-coated electrodes for photosensors, electrochromic display elements and photoresist matrix resins. 

Fig. 9.4. (Left) a seven-segment display including electrochromic display elements based on PEDOT PSS. (Right) the FA 3300/5 Nilpeter label printing press utilized to manufacture electrochemical devices based on PEDOT PSS...

Electrochemical devices such as transistors [13-15] and diodes [16] have been demonstrated using printing techniques. These devices are quite slow ( 0.1 to 10 Hz), but may be acceptable for use in conjunction with printed electrochromic displays—the key advantage is that the devices and the display elements are produced simultaneously using the same process steps. Similarly, passive components and resistor-capacitor circuits have been demonstrated with ink-jet printing [16]. This last example even demonstrated the use of standard staples for interconnecting stacked layers. 

Rodriguez, M.L., R. Aroca, and J.A. DeSaja (1992). Electrochromic properties of Langmuir-Blodgett films of bisphthalocyanine complexes of rare earth elements. Chem. Matter 4,1017. 

Determination of Parameters from Randles Circuit. Electrochemical three-electrode impedance spectra taken on electrochromic materials can very often be fitted to the Randles equivalent circuit (Randles [1947]) displayed in Figure 4.3.17. In this circuit R /denotes the high frequency resistance of the electrolyte, Ra is the charge-transfer resistance associated with the ion injection from the electrolyte into the electrochromic film and Zt, is a Warburg diffusion impedance of either semi-infinite, or finite-length type (Ho et al. [1980]). The CPEdi is a constant phase element describing the distributed capacitance of the electrochemical double layer between the electrolyte and the film having an impedance that can be expressed as... 

However, window applications imply that the entire system, including the counter-electrode, is in the optical path. Hence the counter-electrode must be either optically passive (i.e. colourless in both oxidized and reduced states) or it must be electrochromic in a complementary sense with respect to the working electrode primary element (i.e. colourless in the reduced state and coloured in the oxidized state). 

Electrochromic effects have been observed for the LB films of the phthalocyanines of rare-earth elements. The compressed monolayers of Yb bis-phthalocyanine are found to be sufficiently stable [201]. However, electrochromic switching was observed when altema-... 

The ionic conductor for electrochromic systems is an important element (fig. 35-1). The ions should move fast from the EC-layer into the electrolyte and for battery-type EC-devices to the second EC-layer or the ion-storage electrode. 

FIGURE 16.10. The Periodic Table of the elements, excepting the lanthanides and actinides. The shaded boxes refer to the transition metals whose oxides have well-documented cathodic and anodic electrochromism. (From Granqvist, C., Handbook cf Inorganic Electrochromic Materials, Elsevier Science, 1995. With permission.)... 

It is interesting and important to notice that the electrochromic oxides are based on metallic elements that are located in a well-defined region of the Periodic Table, and, firr-thermore, that different parts of this region pertain to oxides with cathodic and anodic coloration. Already at this point one may draw the conclusion that the electrochromism is closely related to the electronic structure of the oxides this issue is elaborated below. 

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