Transmittance electrochromic materials

The term electrochromism was apparently coined to describe absorption line shifts induced in dyes by strong electric fields (1). This definition of electrocbromism does not, however, fit within the modem sense of the word. Electrochromism is a reversible and visible change in transmittance and/or reflectance that is associated with an electrochemicaHy induced oxidation—reduction reaction. This optical change is effected by a small electric current at low d-c potential. The potential is usually on the order of 1 V, and the electrochromic material sometimes exhibits good open-circuit memory. Unlike the well-known electrolytic coloration in alkaU haUde crystals, the electrochromic optical density change is often appreciable at ordinary temperatures. 

Compared with PEO electrolytes, PDVF, and PMMA electrolytes exhibited higher ionic conductivities. In particular, PMMA has attracted increasing attentions due to its low cost, high solvent retention ability, high transparency, and processibility. The first allpolymer electrochromic device was obtained based on a gel electrolyte and PEDOT-PSS [poly(styrene sulfonate)] electrochromic material (Argun et al., 2003). The fabricated device exhibited a maximum transmittance change of 51% at 540 nm. In addition, this device was fairly stable and only 5% contrast loss was observed after 32,000 cycles. 

Lampert and coworkers [36] have used a modified amorphous PEO-LiCFaSOs electrolyte for the realization of WO3 laminated windows using several types of counter-electrodes, such as niobium oxide, nickel oxide and a new class of solid redox polymerization electrodes [63]. These latter electrodes have an advantage over inorganic layers in that they can be tailored to the electrochromic material and ion specifically. Figure 8.18 illustrates the optical transmittance of a EW made of WOa/modified a-PEO/ion storage polymer [63]. 

The importance of an electrochromic material can be measured by the intensity of the color change between its colored and bleached states. Usually, the intensity of the color change is shown in terms of the thickness-dependent properties such as the change in transmittance (AT), the contrast ratio (CR) or the change in absorbance (AA). Hence the values reported for the same electrochromic material can vary from device to device, depending on the preparation conditions and device design. Using PEDOT, Lim et al. proposed a very convenient and systematic method to predict the thickness for maximum contrast (Lm) of an EC film that is independent of the device characteristics. The ATmax of PEDOT was estimated by Lim et al. to be 48.2 % at ca. 3 cycles [14]. 

Electrochromism. Electrochromic materials have the property of a reversible and visible change in transmittance and/or reflectance associated with an electrochemically induced redox process involving electroactive species typically deposited onto an electrode surface as a thin film. The redox state of the material may be switched by an electron transfer reaction at an electrode and the observed colour change results from the generation of different electronic absorption bands according to the redox state. Such a colour change is commonly reported between a transparent ( bleached ) state and a coloured state, or between two coloured states. or even between multiple coloured states (multichromic). ... 

FIGURE 16.15. Spectral transmittance at three different states of coloration for an electrochromic device of the type shown in the inset. (From Granqvist, C., Handbook of Inorganic Electrochromic Materials, Elsevier Science, 1995. With permission.)... 

One important application of ICPs is electrochromism. The absorption and emission spectra of certain dyes may be shifted by hundreds of angstroms upon application of a strong electric field. This effect is called electrochromism. In other words, Electrochromism is the property of a material where its color is changed by an electrochemical redox reaction. An electrochromic material is the one that changes color in a persistent but reversible manner by an electrochemical reaction and the phenomenon is called electrochromism. Electrochromism is the reversible and visible change in transmittance and/or reflectance that is associated with an elec-trochemically induced oxidation-reduction reaction. The color change is commonly between a transparent ( bleached ) state and a colored state, or between two colored states. These color changes are directly related... 

Electrochromic polymers (ECPs) materials exhibit a change in transmittance and/ or reflectance of electromagnetic radiation induced by an electrochemical oxidation-reduction reaction (called electrochromism) (Rosseinsky and Mortimer, 2001). The ECPs can be used as electrochromic displays, glasses, and even fabrics (Remmele et al., 2015). A certain set of properties, such as, desired absorption profile, easily accessible redox process and ease of processing are of essential importance for materials to serve as effective electrochromes (Dyer and Reynolds, 2007). 

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