Thin films, electrochromic

The electrolyte may be a liquid, a polymer, a gel or a thin film electrolyte. Polymer and gel electrolytes lead to laminated sandwich structures whereby thin film electrolyte (e.g., Ta20s) leads to an aU-thin film electrochromic devices. In this case, EC-devices with only one glass or plastic substrate can be fabricated (O Brian, 1999). Liquid electrolytes are not usefiil for large area applications, because of the budding of the glass and the risk of leakage. Therefore polymer, gel or soUd electrolytes are preferred for large area EC-devices. 

Tetrathiafulvalene (TTE) has also been used in electrochromic devices. TTE-based polymers spin-coated onto transparent electrode surfaces form stable thin films with reproducible electrochromic properties (100). The slow response of these devices has been attributed to the rate of ion movement through the polymer matrix. 

Miscellaneous. Iridium dioxide, like RUO2, is useful as an electrode material for dimensionally stable anodes (DSA) (189). SoHd-state pH sensors employing Ir02 electrode material are considered promising for measuring pH of geochemical fluids in nuclear waste repository sites (190). Thin films (qv) ofIr02 ate stable electrochromic materials (191). 

Members of the ion-insertion/extraction group, as inorganic or organic thin films, especially the former, have attracted the widest interest most recently. Tungsten trioxide was the eadiest exploited inorganic compound (4), even before the mechanism of its electrochromic response was understood (5). It is stiU the best known of the important ion-insertion/extraction group. 

Spatial electrochromism has been demonstrated in metallopolymeric films.28 Photolysis of poly-[Run(L10)2(py)2]Cl2 thin films on ITO glass in the presence of chloride ions leads to photochemical loss of the photolabile pyridine ligands, and sequential formation of po/y-[RuII(Llt))2(py)Cl]Cl and po/y-[Run(L10)2Cl2] (Scheme 1). 

The electrochromism of the phthalocyanine ring-based redox processes of vacuum-sublimed thin films of [Lu(Pc)2] was first reported in 1970,32 and since that time this complex has received most attention, although many other (mainly lanthanide) metallophthalocyanines have been investigated for their electrochromic properties.1 Lu(Pc)2 has been studied extensively by Collins and Schiffrin33,34 and by... 

The LB technique is amenable to the fabrication of ECDs as demonstrated by the report of a thin-film display based on bis(phthalocyaninato)praseodymium(III).75 The electrochromic electrode in the display was fabricated by deposition of multilayers (10-20 layers, r+00-200 A) of the complex onto ITO-coated glass (7 x4cm2) slides. The display exhibited blue-green-yellow-red polyelectrochromicity over a potential range of —2 to +2V. After 105 cycles no significant... 

In addition, the integration of modem optical technology and electrochemical techniques for sensing applications appears to be a powerful new approach. A new type of optoelectrochemical sensor for chlorine, based on an electrochromic thin-film sensing layer placed on top of a planar waveguide, has demonstrated the applicability of this combined approach. 

D. Ellis, M. Eckhoff, and V.D. Neff, Electrochromism in the mixed-valence hexacyanides. 1. Voltammetric and spectral studies of the oxidation and reduction of thin films of Prussian Blue. J. Phys. Chem. 85, 1225-1231 (1981). 

Porqueras, I. Person, C. Corbella, C. Vives, M. Pinyol, A. Bertran, E. 2003. Characteristics of e-beam deposited electrochromic Ce02 thin films. Solid State Ionics 165 131-137. 

Brezesinski, T. Fattakhova-Rohlfing, D. Sallard, S. Antonietti, M. Smarsly, B. M. 2006. Highly crystalline W03 thin films with ordered 3D mesoporosity and improved electrochromic performance. Small 2 1203-1211. 

Sallard, S. Brezesinski, T. Smarsly, B. M. 2007. Electrochromic stability of W03 thin films with nanometer-scale periodicity and varying degrees of crystallinity. /. Phys. Chem. C 111 7200-7206. 

Optical waveguide detection of photoinduced electrochromism in ultra-thin films... 

Figure 28 Schematic representa- Figure 29 Changes in the OWG absorbance of PV2+(TFPB )2 tion of the OWG system for detect- thin films of various thickness during IPCT excitation ing photoinduced electrochromism (a) 10.0, (b) 40.4, (c) 64.9, (d) 955, and (e) 179.6 nm. of ultrathin films (S) in the evacuation chamber shown in an inset.

In situ UV-visible spectroscopy monitors the energy of electrons within the analyte. While, strictly speaking, all materials change their UV-visible spectrum in accompaniment with electrode reactions (they are said to be electrochromic), the majority of these changes are not discernible by the human eye, and therefore may not be useful to the analyst. Electrodes must be optically transparent for in situ work, with the most commonly used being a thin film of the semiconductor, indium-tin oxide, on glass. 

The author was brought up in Hastings, on England s south coast, where he attended a local comprehensive school. Despite this education, he achieved entrance to the University of Exeter to read Chemistry. Having obtained a B.Sc. degree and then a doctorate (in 1989) on the electrochemistry of the viologens, he was awarded a fellowship at the University of Aberdeen to study the electrochromism of thin films of tungsten trioxide. 

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 ... 

Examples for electrochromic behavior upon electrochemical oxidation can be found among group VIII metal oxides. Thin films of transparent hydrated iridium oxide turn blue-black, whereas nickel oxide switches from pale green to brown-black, possibly due to the absorbance of Ni3+ centers [26]. The systems are much less thoroughly investigated and a detailed mechanistic explanation is not known. However, proton extraction and anion insertion have been suggested. 

Photochemical polymerization of dithiophene 325 in acetonitrile in the presence of CC14 and TBABr leads to a thin film with electrochromic properties in the visible region (94JCS(CC)1911 95SM(69)309). Laser flash photolysis in the presence of CC14 showed absorption at 417 nm due to the radical cation. 

Iridium oxide, Ir02, is used in the fabrication of thin films for stable electrochromic materials and as an electrode material. Iridium metal is used in the manufacture of fountain pen points, airplane spark plugs, and hypodermic needles, see also Inorganic Chemistry. 

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