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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early 2000, triarylamine (TA)‐based aromatic polymers especially the PIs and PAs have drawn considerable attention from the research community as the fourth‐generation EC materials. The correlation between electrochemical properties and chemical structures of different aromatic PIs was firstly described in 1990. Ten years later, Zhiyuan Wang and coworkers [14] reported the first EC behavior of poly(ether naphthalimide)s, which showed stepwise coloration process, from colorless to red and to dark blue corresponding to the neutral, radical anion, and dianion species, respectively. However, due to the high rigidity of the PIs/PAs backbone and strong intermolecular interactions, the poor processability limited the development of PIs or PAs EC materials. Therefore the TA groups were introduced to the PIs/PAs backbone to improve the solubility of aromatic polymers. The first TA‐based polyamide PA was synthesized in 1990 [15], and the first aromatic polyimides integrating interesting EC properties containing TA groups were disclosed in 2005 [16]. Since then, Liou, Hsiao and, other groups have developed numerous TA‐based EC PIs/PAs. Most of the PIs/PAs were solution processible and thermally stable with excellent adhesion with indium tin oxide‐coated glass electrode and had good electrochemical stability. Now the TPA‐based PIs/PAs are considered as great anodic EC materials due to proper oxidation potentials, electrochemical stability, and thin‐film formability.

      More recently, with the active researches on the crystalline and porous MOFs and COFs, the sixth‐generation MOFs/COFs EC materials have emerged. In 2013, the first EC properties of MOFs using naphthalene diimide (NDI) as organic linker were reported by Professor M. Dinca's group [19]. And the first COFs EC material using the TPA as building block was revealed by Yuwu Zhong and Dong Wang and coworkers in 2019 [20]. All in all, some essential features of MOFs/COFs give them advantages in EC, including designable and precise molecular structure, simple self‐assembly synthesis, and porous structure that facilitate the electrolyte ions transport. However, these new EC materials haven't been fully revealed; many efforts should be taken to improve the device performance of MOFs/COFs‐based electrochromism.

Graphs depict the spectroelectrochemistry (SEC) of a black-to-transmissive EC material. (a) Absorbance model and (b) transmittance model.

      Source: Reproduced by permission Li et al. [21]. © 2018, Royal Society of Chemistry.

      1.3.1 Electrochromic Contrast

Graphs depict (a) The electrochromic contrast of a small molecule EC material. (b) sensitivity function of the human eye V(λ) and luminous efficacy vs wavelength. (c) The change of the lightness values from the neutral to the oxidized states.

      Source: Jiang et al. [23]

      , (b) sensitivity function of the human eye V(λ) and luminous efficacy vs wavelength.

      Source: Fred Schubert [24]. © 2006, Cambridge University Press.

      (c) The change of the lightness values from the neutral to the oxidized states.

      Source: Li et al. [21]. © 2018, Royal Society of Chemistry.

      Except for the aforementioned method for electrochemical contrast measurements, a photopically weighted value called photopic contrast was proposed by Javier Padilla et al. [26]. The photopic contrast also reflects an overall contrast during the whole visible region, which is more consistent with the real application condition. It can be calculated using the following equation:

upper T Subscript photopic Baseline equals StartFraction integral Subscript lamda Subscript min Baseline Superscript lamda Subscript max Baseline Baseline upper T left-parenthesis lamda right-parenthesis upper S left-parenthesis lamda right-parenthesis upper P left-parenthesis lamda <hr><noindex><a href=Скачать книгу