Solution-Solid Electrochromes

Optical memory (open-circuit memory). Optical memory is defined as the time that an electrochromic material maintains its absorption state once the applied voltage is removed. Solution-based electrochromic systems will bleach (lose their absorptive state) more quickly than their solid-state counterparts [24]. In the solution case, the mobile redox-active species, which are dissolved in an electrolyte, can diffuse to both electrodes when the circuit is open. Therefore, there is no open-circuit memory in these devices and power must be supplied continuously to maintain coloration. 

Doped silicon, conductivity in, 23 35 Doped/undoped electrochromic organic films, 6 580-582 Dope-dyeing, 9 197 Dope-making process, in acrylic fiber solution spinning, 11 204 Dope solids, in air gap spinning, 11 209 Doping, 23 838—839 calcium, 23 842-844 conducting polymers, 7 528-529... 

The first demonstration of a PEM with electrochromic properties was disclosed by SchlenofFand coworkers [66], using poly(butanylviologen)/ PSS films. While this film exhibited strong electrochromic response, it still required the use of an outer electrolyte solution. DeLongchamp and Hammond disclosed for the first time a solid-state device comprised of two electrochromic PEM-modified ITO electrodes separated by a 200-p,m thick poly(2-acrylamido-methane-2-propanesulfonic acid), proton-conducting PAMPS membrane (see Eigure 2.30) [196]. Both PEMs used in... 

The materials that change colour on passing a charge are called electrochromes, and these can be classified into three groups. In the first type the colouring species remain in solution in the second type the reactants are in solution but the coloured product is a solid the third type are those where all the materials are solids, e.g. in films. The first type is used in car, anti-dazzle, rear-view mirrors, the second type in larger mirrors for commercial vehicles and the third type in smart windows (see section 1.5.4.2). 

The electrochemical behavior of poly(ferrocenylsilanes) has been studied at three levels—in solution by cyclic voltammetry, as films deposited on electrodes, and in the solid state via iodine doping. Solution cyclic voltammetric oxidation and reduction has shown that the polymer, where R/R is Me/Me, reversibly oxidizes in methylene chloride in two stages, apparently with the first oxidation being on alternating iron atoms along the chain.29 Films cast on electrodes behave in a similar way and also show an electrochromic response to oxidation and reduction.30... 

Electrochromic materials are of three basic types [i]. In a given -> electrolyte solution, type I materials are soluble in both the reduced and oxidized (redox) states, an example being l,l -di-methyl-4,4 -bipyridylium ( methyl viologen ), which, on reduction, switches from the colorless di-cation to the blue radical cation. Type II materials are soluble in one redox state, but form a solid film on the surface of an electrode following electron transfer. An example here is l,l -di-heptyl-4,4 -bipyridylium ( heptyl viologen ). In type III materials, such as -> tungsten oxide, - Prussian blue, and electroactive conjugated polymers, both... 

Electrochromic devices using poly(3-octylthiophene) associated to vanadium oxide as cathodically colouring material and a solution of polyethylene oxide (PEO) mixed with lithium perchlorate as solid electrolyte were tested [12]. Bithiophene properties were also discussed... 

This electrochromic was mainly investi ted with aqueous electrolyte solutions 605 -607,626) nd solid electrolytes . Non-aqueous electrolyte solutions, LiAsFg/ 2-Me-THF and NaAsFg/PC, were ured for the insertion of Li and Na McIntyre et al. the reported response times are 10 to 20 s. 

While an invaluable tool in producing conjugated polymers on conducting substrates, electropolymerization has limitations that include a lack of primary structure verification and characterization along with the inability to synthesize large quantities of processable polymer. To overcome the insolubility of PEDOT, a water-soluble polyelectrolyte, poly(styrenesulfonate) (PSS) was incorporated as the counterion in the doped PEDOT to yield the commercially available PEDOT/PSS (Baytron P) (39), which forms a dispersion in aqueous solutions [140]. While this polymer finds most of its application as a conductor for antistatic films, solid state capacitors, and organic electronic devices, its electrochromism is distinct and should not be ignored. 

The physical classification dilTerentiates three types of electrochromic materials. Type I electrochromic materials are always in solution. MetaUic ions belong to this class. Type II electrochromic materials are colourless and in solution at one state and coloured and solid at the other state. Heptyl viologen is type II. Type in electrochromic materials are always solid. Most electrochromic materials are type HI, including conducting polymers or metal oxides [59,60]. 

In addition to possible roles as the active electrochromic material, it should be recognized that polymers may also be used in electrochromic devices as electrolyte solution thickeners, as plasticizers, as the matrix or solid phase of gels, as solid polymer electrolytes, and even as sealants to insulate a glass imit configuration... 

By combining an electrically conductive polymer (e.g. POT) prepared by spin coating from solution with a solid polymer electrolyte and a metal oxide, a sohd state electrochromic device is constructed [713]. Substrates coated with PT can be used in electrochromic displays, in solar cells (cf Sect. 6.3), and for corrosion protection [714]. Poly(3,4-ethylenedioxythiophene-2,5-diyl), which has good electrochromic properties, (for structure cf Sect. 1.2) can used as an electrode in a solid state electrochromic cell (cf Sect. 3.4.3) [43]. PITN can be reversibly cation- and anion-doped without decomposition. This polymer, with... 

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