Polymer electrochromic materials

Gaupp, C.L., Welsh, D.M., Ranh, R.D., and Reynolds, J.R. 2002. Composite coloration efficiency measurements of electrochromic polymers based on 3,4-alkylenedioxythio-phenes. Chemistry of Materials 14, 3964—3970. 

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). 

Gunbas, G.E., Durmus, A., Toppare, L., 2008. Could green be greener Novel donor-acceptor-type electrochromic polymers towards excellent neutral green materials with exceptional transmissive oxidized states for completion of RGB color space. Adv. Mater. 20,691-695. 

Solid-state systems of particular interest in this book are conductive polymers with the ability to occlude dopants entering the bulk of the polymer sample, thus conferring on it its special electrical properties. Some of these properties are a consequence of the mobility of the dopant ions in the host polymer material, and these properties are responsible for such technological applications as battery electrodes,ion gates, and electrochromic devices, which depend on a field-induced oxidation of the polymer specified by its doping level. Various diffraction methods and tunnelling electron microscopy reveal that these... 

In a dual polymer ECD, the redox-active material at both electrodes is an electrochromic polymer, while in a hybrid device the material at the working electrode is an electrochromic polymer and the material at the counter electrode is an inorganic (e.g., WO3 or PB) or molecular organic (e.g., polyviologen) electrochrome [4,5,16,239,249,250]. 

The combination of various device platforms, along with electrochromic polymers available in colors that span the entire range of the visible spectrum and beyond, allows the construction of displays that can be tailored to fit most needs in real applications. While these devices have shown enhanced performance in colors available, optical memory, and low power consumption as compared to devices constructed of other electrochromic materials, there are still drawbacks to be addressed. 

Poly (thiophene)s are of particular interest as electfochromic materials owing to their chemical stability, ease of synthesis and processability. For the most part, current research has been focused on composites, blends and copolymer formations of several conjugated polyheterocyclics, polythiophene and its derivatives, especially PEIX)T. In one example, poly(3,4-ethylenedioxythiophene) (PEDOT)/poly(2-acrylamido-2-methyl-l-propanesulfonate) (PAMPS) composite films were prepared by Sonmez et al. for alternative electrochromic applications [50]. Thin composite films comprised of PEDOT/PAMPS were reported to switch rapidly between oxidized and neufial states, in less than 0.4 s, with an initial optical contrast of 76% at A.max. 615 nm. Nanostructured blends of electrochromic polymers such as polypyrrole and poly(3,4-ethylenedioxythiophene) were developed via self-assembly by Inganas etal. for application as an electrochromic window [26]. Uniir etal. developed a graft-type electrochromic copolymer of polythiophene and polytetrahydrofuran for use in elecfiochromic devices [51]. Two EDOT-based copolymers, poly[(3,4-ethylenedioxythiophene)-aZ/-(2,5-dioctyloxyphenylene)] and poly[(3,4-ethylenedioxythiophene)-aft-(9,9 -dioctylfluorene)] were developed by Aubert et al. as other candidates for electrochromic device development [52],... 

Thiophene-based Electrochromic Materials 777 Table 20.2 Electrochromic polymers with colors in both doped and undoped states... 

Polythiophenes with P-alkyl substituents including more than three carbon atoms are commonly soluble in organic solvents. Recently, electrochromic polymers such as poly(thiophene-3-acetic acid) and its copolymer with polythiophene were prepared. The electrochromic properties of these materials were studied by observing a color change from red to black during the potential sweep with a stability for 264 cycles, establishing a high electrochromic efficiency of up to 242 cm C at 750 nm [65],... 

Types of Electrochromic Materials. Electrochromic materials are of three basic types (2). In a given electrolyte solution, type I materials are soluble in both the reduced and oxidized (redox) states. Type II materials are soluble in one redox state, but form a solid film on the surface of an electrode following electron transfer. Electrochromic polymers are examples of type III materials, where both redox states are solids, generally studied as thin films on electrode surfaces. For types II and III, once the redox state has been switched, no further charge injection is needed to retain the new electrochromic state, and such systems are said to have optical memory . In contrast, for type I electrochromic materials, diffusion of the soluble electrochemically-generated product material away from the electrode occurs and it is necessary to keep current flowing until the whole solution has been electrolyzed. 

Further developments in the field of electrochromic polymers seem limited only by the skills, resources, and imagination of synthetic organic chemists, polymer chemists, and material scientists. However, the ultimate usefulness of such fascinating materials hinges on a detailed understanding of their fiindamental redox operation and the accompanying physicochemical-structural changes, and therefore the field is truly interdisciplinary. 

A better understanding of intrinsic properties of electrochromic polymer films (such as the electrical, optical and structural properties) and of the tehavior of these films at different interfaces (such as electrode surface and electrolyte solution) will permit in rovement in the design (electrode materials, conq)osition of siq>port electrolyte, contacts, etc.) and performance of ECDs. Usefol information t is needed includes ... 

Synthesis, Properties, and Applications of Photochromic Amorphous Molecular Materials and Electrochromic Polymers... 

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