Organic Electronics for Electrochromic Materials and Devices. Hong Meng

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Organic Electronics for Electrochromic Materials and Devices - Hong Meng


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Graph depicts the solar irradiance spectrum above atmosphere and at the surface of the Earth.

      Source: Nick84: https://commons.wikimedia.org/wiki/File:Solar_spectrum_en.svg, Licensed under CC BY‐SA 3.0.

Schematic illustration of the scheme of three types of electrochromic devices.

Schematic illustration of the roadmap of EC materials development.

      Following the first‐generation TMO EC materials, organic small molecule EC materials have emerged since 1970. Among them, viologen as the most representative small molecule was first discovered by Michaelis and Hill in 1932 [10], and because of the violet on the reduction, these 1,1′‐disubstituted‐4,4′‐bipyridine compounds were named “viologen.” Then in 1973, Shoot made a new flat alphanumeric display using heptyl viologen; this can be regarded as the beginning of the use of viologen for electrochromism [11]. After a century's development, viologen already has been successfully commercialized. Besides the viologen, other small molecules EC materials such as terephthalate derivatives, isophthalate derivatives, methyl ketone derivatives, and some dye molecules have also attracted much attentions from scientists due to their simple structure and low cost.

      The third‐generation EC materials are conjugated polymers. In 1983, Francis Garnier and coworkers firstly characterized the EC properties of a series of five‐membered heterocyclic polymers including poly(pyrrole), poly(thiophene), poly(3‐methylthiophene), poly(3,4‐dimethylthiophene), and poly(2,2′‐dithiophene). Since then, conjugated polymers were given rise to the rapid emerge as a new class of electrochromism [12]. Five years later, Berthold Schreck observed the electrochromism phenomenon of poly(carbazole), which showed a color change from pale yellowish to green together with the conductivity enhancement [13]. To date, the conjugated polymer EC system has been well developed, from better understandings on mechanisms to completed color pallette with soluble or electro‐deposited polymers, and even full‐color display samples or roll‐to‐roll fabricated flexible


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