Electrochromism Dynamic Range

Akhtar et al. [902(a)] were one of the first to describe completely assembled, sealed, solid-state electrochromic devices based on CPs. In one set of devices, the fairly common Li-triflate/Poly(ethylene oxide) (PEO)/acetonitrile formulation for nonaqueous solid electrolytes was used. However, in another set, the unique combination of poly(ethyleneimines) of different MWt and protonic acids such as hydrochloric, sulfuric, phosphoric, acetic and poly(styrene sulfonic) was used. Additionally, the films of the CP, P(ANi), were prepared electrochemically as well as by sublimation, and in one set of devices Fe-tungstate was used as a counter electrode to provide a definitive counter electrode reaction (Lithiation). While cyclabilities to several thousand cycles were claimed, the electrochromic dynamic range and other parameters were fairly poor, as seen in Figs. 20-3. Very rapid switching times have been claimed for many P(ANi)- or P(ANi)-derivative based devices. For example. Ram et al. [902(b)] claimed a 143 ms switching time for liquid-electrolyte devices based on poly(aniline-co-o-anisidine). 

Table 1 shows typical emittance data for two devices. The emittance data may be compared with the variation observed in extant mechanical louvers, ca. 0.16 to 0.56 Ae = 0.4) (3). We also note that, to the best of our knowledge, these dynamic range (i.e. light/dark electrochromic contrast) values, e.g. > 50% Reflectance at 3 to 12 ftm (Figure 3) and Ae> 0.5 (Table I), represent the largest dynamic (i.e. switchable) IR signature variation in arsy material... 

Subsequent to our original work in 1995 (4), Topart s group (7) reported on the IR electrochromism of a P(ANi)/(CSA)/liquid electrolyte (1.0 M HCIO4) system. They observed a dynamic range for Specular reflectance of ca. 35% at 10... 

Write out detailed definitions, with illustrations if appropriate, for the following terms Chronovoltabsorptometry oxidative and reductive Switching Times Electrochromic, Electrochemical and Charge Cyclabilities Charge Capacity Dynamic Range Open Circuit Memory Bandgap Solar Absorptance Thermal Emittance. 

We must needs start this chapter by making the important observation that, although there is a surfeit of studies of the electrochromic properties of a wide variety of CPs in a laboratory environment, there is a dearth of studies of actual, practical devices. Furthermore, there is an even greater dearth of examples of commercial implementation of CP-based electrochromic devices. The tests in laboratory environments typically involve looking at the spectroelectrochemical characteristics of a CP film deposited chemically or electrochemically on a transparent conductive electrode such as ITO/glass in a liquid-electrolyte containing cell. A plethora of such studies have been cited in Chapter 3 earlier, and the reader is referred to these for an appreciation of the multitude of colors, dynamic ranges and other performance characteristics obtainable with CP-based electrochromics. 

All the electrochromic performance parameters cited earlier in Chapter 3 are valid equally for electrochromic devices as for laboratory-cell electrochromic systems Dynamic range switching time cyclability open circuit memory. The reader is referred to this chapter for further reference and definitions. 

Redefine the following terms as they pertain to electrochromic devices Dynamic range switching time cyclability open circuit memory optical memory broad-band. 

A special case are ion storage layers with complementary electrochromic activity, which may be assembled with a PEDOT layer. In a complementary electrochromic cell, both layers—dye and bleach—simultaneously increase to the overall optical contrast. Tungsten trioxide as well as Prussian Blue, iron(III) hexacyanoferrate(II/III) bleach upon reduction and were used in combination with PEDOT. Cells made from PEDOT in combination with Prussian Blue exhibited a deep blue-violet color at a potential of -2.1 V and become light blue at 0.6 V. Combination cells of alkylenedioxypyrrols or -thiophenes with ferrocene have been proposed as variable optical attenuator devices due to a large dynamic range of optical attenuation at the telecommunication wavelength of 1550 nm. ... 

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