A review of electrochromic (EC) polymers and their applications in absorption/transmission, reflective, and patterned electrochromic devices (ECDs) is presented. Fundamental properties of EC materials such as optical contrast, coloration efficiency, switching speed, and stability are described along with the commonly used characterization methods. The origin of electrochromism in conjugated polymers is explained in terms of the electronic structure changes in the backbone upon doping/dedoping. The ability to tailor the EC properties of conjugated polymers and tune their color states via modification of the polymer structure is demonstrated. Multicolor electrochromic materials can be obtained by substitution of a parent polymer and controlled polymerization of comonomers and with blends and laminates of homopolymers. Absorption/transmission-type ECDs from complementarily colored polymers and reflective-type ECDs on metalized substrates are illustrated with several examples from the literature. Finally, several patterning methods that are promising for ECD applications are discussed. Examples of ECDs constructed from patterned electrodes using line-patterning, screen-printing, and metal vapor deposition techniques are investigated for their possible use in commercial applications.

The ability to match two complementary polymers constitutes an important step forward in the design of electrochromic devices (ECDs). Here we show that the necessary control over the color, brightness, and environmental stability of an electrochromic window can be achieved through the careful design of anodically coloring polymers. For this purpose, we have constructed ECDs based on dimethyl substituted poly(3,4-propylenedioxythiophene) (PProDOT-Me 2 ) as a cathodically coloring layer, along with poly[3,6-bis(2-ethylenedioxythienyl)-N-methyl-carbazole] (PBEDOT-NMeCz) and N-propane sulfonated poly(3,4-propylenedioxypyrrole) (PProDOP-NPrS) as anodically coloring polymers. Comparison of the results shows that using PProDOP-NPrS as the high band gap polymer has several advantages over the carbazole counterpart. The main benefit is the opening of the transmissivity window throughout the entire visible spectrum by moving the π-π* transition of the neutral anodically coloring material into the ultraviolet region. Another advantage of the PProDOPNPrS based device is the noticeable increase in the optical contrast as evidenced by an increase in the transmittance change of the device (∆%T) from 56% to 68%, as measured at 580 nm. These devices exhibit a 60% change in luminance along with half-second switching times for full color change. Moreover, they were found to retain up to 86% of their optical response after 20 000 double potential steps, opening up new directions in optical technology.

A series of electrochromic N-substituted poly(3,4-propylenedioxypyrrole)s (PProDOPs) are reported, which exhibit the combined properties of a high (>3 eV) electronic band gap, colored oxidatively doped forms, and easily accessible, low redox potentials. Utilizing methyl (Me), propyl (Pr), octyl (Oct), propanesulfonated (PrS), and ethoxyethoxyethanol (Gly) pendants, the absorbance of the π−π* transition of the resulting polymers is blue-shifted when compared to the nonderivatized parent. For example, in the case of poly(N-ethoxyethoxyethanol ProDOP) (N-Gly PProDOP), this transition displays a maximum at 306 nm (onset at 365 nm), providing a colorless and highly transparent neutral polymer with a luminous transmittance greater than 99% for a film thickness of about 200 nm. N-Substituted PProDOPs display very well-defined cyclic voltammograms, with E 1/2 < −0.1 V vs Fc/Fc+ (+0.2 V vs SCE), negative of the oxidation of water, as desired for materials having stable doped forms and long-lived redox switching properties. In addition, the presence of a sulfonate group at the end of the propyl chain in N-PrS PProDOP offers the possibility of self-doping along with water solubility of the polymer. As a result, N-PrS PProDOP exhibits a fast and regular growth even in the absence of supporting electrolyte. This new family of polymers has not only shown interesting electrochromic properties in the visible. Upon doping, a very strong absorption is observed in the near-infrared (NIR) with changes in transmittance up to 97%, extending the use of these polymers as the active layer in vis−NIR switchable devices.