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Electrochromism And Electrochromic Devices
Published in P.J. Gellings, H.J.M. Bouwmeester, Electrochemistry, 2019
An electrochromic material is able to change its optical properties when a voltage is applied across it. The optical properties should be reversible, i.e., the original state should be recoverable if the polarity of the voltage is changed. These properties make electrochromic materials of considerable interest for optical devices of several different types, such as elements for information display, light shutters, smart windows, variable-reflectance mirrors, and variable-emittance thermal radiators. This chapter reviews the basic materials background and the state of the art for electrochromic devices. Electrochromism is well known in numerous inorganic and organic substances; the chapter is devoted to the former class. Almost all of the interesting materials are oxides that are employed in the form of thin films.
Introduction to Organic Electrochromic Materials and Devices
Published in Sam-Shajing Sun, Larry R. Dalton, Introduction to Organic Electronic and Optoelectronic Materials and Devices, 2016
Electrochromics are materials, substances, or devices, which change color generally when a small voltage is applied to them. Their electrochromism is generally based on a chemical oxidation/reduction (redox) process. This definition excludes effects, which appear to be similar, such as solvatochromism, thermochromism, and the effect responsible for the function of light-emitting diodes. Organic electrochromics are predominantly of two classes: conducting polymers (CPs), such as poly(aniline), and nonpolymeric organic materials such as methyl viologens. Electrochromics can encompass not only the visible spectral region but other regions as well, ranging from near- UV to far-IR and microwave–mm-wave. A basic understanding of electrochemistry is essential for understanding the functioning of electrochromics, and this chapter provides one, discussing such significant points as two- vs. three-electrode mode operation and the interpretation of voltammograms from an electrochromic point of view. A subsection is also devoted to CPs, which form by far the bulk of organic electrochromics. Basic electrochromic devices are then presented and their functioning discussed at some length. The methodology and terminology of the measurement of electrochromism, for both transmission- and reflectance-mode devices, is then discussed. The precise definitions of other electrochromic metrics, such as switching time, cyclability, and open circuit memory (optical memory) are then discussed. Finally, the practical-world applications of electrochromics in the visible, IR, and microwave regions, ranging from automobile rearview mirrors and sunglasses to military IR camouflage, are very briefly presented.
Nanotechnology and Energy
Published in Stephen L. Gillett, Nanotechnology and the Resource Fallacy, 2018
Unwanted solar heating is of course also important, at least in summer. Using electrochromic layers to darken windows has attracted attention for decades.63 Electrochromic materials change color under an applied electric field. Much research has been directed toward lithium ion intercalation into tungsten trioxide (WO3),64 already described above (p. 214). On such intercalation, the window becomes reflective, becoming transparent again when the polarity is reversed. Obviously, constructing such a window, particularly of significant area, presents a nanofabrication challenge.
Comparison of vanadium oxide thin films deposited from commercial and solution combustion synthesised powders
Published in Surface Engineering, 2020
M. Seref Sonmez, Esma Yilmaz, Duygu Kalkan, Esra Ozkan Zayim
Electrochromic materials changed their colour by intercalating metal ions and electrons (coloured state) and showed reversibility from coloured state to the bleached state by de-intercalating metal ions and electrons. Furthermore, coloration efficiency (CE) was used in order to point out the difference in optical density (OD) variation per unit area of charge (Q) intercalated/deintercalated in the system [34]. ECD having higher CE value exhibited larger optical variation range that could be succeeding even with a small intercalation/deintercalation ion number [35]. It was calculated by Equation (5):where ΔOD is the optical transmittance change as a function of natural logarithm of the bleached (deintercalation of Li+ ion or discharge of the thin film, Tb) and coloured (intercalation of Li+ ion or charge of the thin film, Tc) states’ transmittance values, Qi is the amount of the charge during intercalation which was found by integrating area under the curve of CA graph (Figure 5(b)). CE value was found to be 36.8 cm2 C−1 at 630 nm. This value was compatible with the previous studies [13,36].
Solar shading devices integrating smart materials: an overview of projects, prototypes and products for advanced façade design
Published in Architectural Science Review, 2019
Two families of smart materials for architecture and design professions have been considered in this review: Type 1 – property-changing smart materials and Type 2 – energy-exchanging smart materials (Addington and Schodek 2005). Type 1 includes chromics or colour-changing smart materials (Freewan 2015). In solar shading devices, there are applications of: photochromic materials: materials that change colour when exposed to light;thermochromics: materials that change colour due to temperature changes;electrochromic materials: materials that change colour when a voltage is applied (Misawa et al. 2014).
Molecular design of supramolecular polymers with chelated units and their application as functional materials
Published in Journal of Coordination Chemistry, 2018
Igor E. Uflyand, Gulzhian I. Dzhardimalieva
In recent years, MEPEs have been widely developed as a new field of electrochromic applications [160]. As the applied potential is increased, the metal centers are oxidized to a higher valence state, and the MLCT decreases. In particular, MEPEs readily form thin films with high optical quality using a variety of methods, including layer-by-layer (LbL) deposition or a coating with linear and continuous film growth [161]. In addition, MEPE thin films immobilized on transparent conductive electrodes show the desired electrochromic properties with high switching rate and low switching potential, since a change in the redox state is usually associated with a change in optical properties. These films can be used for electronic displays and devices, such as electronic papers or electrochromic windows (smart windows).