Electrodes, transparent

Although its use as a transparent electrode in diodes has made it one of the most useful of the conductive polymers, the intractable nature of the material made the stmcture of polyaniline difficult to determine. Recent studies of polyphenyleneamineimines have conclusively shown that the stmcture of PANI is an exclusively para-linked system (21). 

Polyaniline (PANI) can be formed by electrochemical oxidation of aniline in aqueous acid, or by polymerization of aniline using an aqueous solution of ammonium thiosulfate and hydrochloric acid. This polymer is finding increasing use as a "transparent electrode" in semiconducting devices. To improve processibiHty, a large number of substituted polyanilines have been prepared. The sulfonated form of PANI is water soluble, and can be prepared by treatment of PANI with fuming sulfuric acid (31). A variety of other soluble substituted AJ-alkylsulfonic acid self-doped derivatives have been synthesized that possess moderate conductivity and allow facile preparation of spincoated thin films (32). 

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. 

Tin oxide and indium oxide [1312-43-2] Iu202, are other important semiconductors that are doped to increase conductivity. Sn02, Iu202, Ti02, and in particular, SrTiO, are transparent to visible light and are often used as transparent electrodes, for example, on vidicon tubes. 

The changes in the optical absorption spectra of conducting polymers can be monitored using optoelectrochemical techniques. The optical spectmm of a thin polymer film, mounted on a transparent electrode, such as indium tin oxide (ITO) coated glass, is recorded. The cell is fitted with a counter and reference electrode so that the potential at the polymer-coated electrode can be controlled electrochemically. The absorption spectmm is recorded as a function of electrode potential, and the evolution of the polymer s band stmcture can be observed as it changes from insulating to conducting (11). 

Optically transparent electrodes (OTEs), which enable light to be passed through their surface and the adjacent solution, are the keys for performing transmission... 

FIGURE 2-10 Thin-layer spectroelectrochemical cell. OTE = optically transparent electrode. 

W Heineman, F. Hawkridge and H. Blount, Spectroelectrochemistry at Optically Transparent Electrodes in A.J. Bard, Ed., Electroanalytical Chemistry, Vol. 13, Marcel Dekker, New York, 1986. 

Ohmic drop, 32, 88, 105, 129 Operational amplifier, 105 Optically transparent electrode, 40 Organic-phase biosensors, 181 Organic solvents, 102 Organosulfur monolayers, 118 Overvoltage, 14, 121 Oxygen, 75, 87, 103, 177, 190, 193... 

Fig. 5.19 (a) Linking CdSe quantum dots to Ti02 particle with bifunctional surface modifier (b) light harvesting assembly composed of T102 film functionahzed with CdSe Q-dots on optically transparent electrode (OTE). [Adapted (in gray scale) from [348]]... 

Figure 33.1a illustrates the idea of the smart window. In this device a layer of electrochromic material and a layer of a transparent ion-conducting electrolyte are sandwiched between two optically transparent electrodes (OTEs). Indium-doped tin oxide on glass is used most commonly as the OTE. This material has very low... 

Relatively little work has been done on ORR catalysis by self-assembled mono-layers (SAMs) of metalloporphyrins. The advantages of this approach include a much better defined morphology, structure, and composition of the catalytic film, and the surface coverage, and the capacity to control the rate at which the electrons ate transferred from the electrode to the catalysts [CoUman et al., 2007b Hutchison et al., 1993]. These attributes are important for deriving the catal5d ic mechatfism. The use of optically transparent electrodes aUows characterization of the chemical... 

Semiconductors. In Sections 2.4.1, 4.5 and 5.10.4 basic physical and electrochemical properties of semiconductors are discussed so that the present paragraph only deals with practically important electrode materials. The most common semiconductors are Si, Ge, CdS, and GaAs. They can be doped to p- or n-state, and used as electrodes for various electrochemical and photoelectrochemical studies. Germanium has also found application as an infrared transparent electrode for the in situ infrared spectroelectrochemistry, where it is used either pure or coated with thin transparent films of Au or C (Section 5.5.6). The common disadvantage of Ge and other semiconductors mentioned is their relatively high chemical reactivity, which causes the practical electrodes to be almost always covered with an oxide (hydrated oxide) film. 

Electrochemically generated products can be readily characterized by in situ measurement of their absorption spectra in the ultraviolet and visible regions. Optically transparent electrodes (OTEs) prepared from thin layers... 

Figure 2.2 The transparent electrodes in an LCD are coated with crossed polarizers. The liquid crystals (depicted as slender lozenges) form helices, thereby guiding polarized light from the upper electrode through the LCD, enabling transmission through to the lower polarizer. This is why the display has no colour. The helical structure is destroyed when a voltage is applied, because the polar liquid crystals align with the electrodes field. No light can transmit, so the display looks black...

Solution-cast films of polyaniline optical quality transparent electrodes... 

Y Cao, GM Treacy, P Smith, and AJ Heeger, Solution-cast films of polyaniline optical-quality transparent electrodes, Appl. Phys. Lett., 60 2711-2713, 1992. 

Unlike the constraints on anode material, the constraints on cathode materials are usually lower because typically they do not need to constitute the transparent electrode material. In certain instances, where a completely transparent OLED is needed (windshield and heads-up displays), ITO may also be used as the cathode with suitable modification [12]. In general, cathode materials are pure metals or metal alloys. The requirements for cathode materials are as follows ... 

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