Abstract
Electrochromic (EC) polymers such as polyviologens have been attracting considerable attention as wet-processable electrodes for EC displays, thanks to their brilliant color change accompanied with reversible redox reactions. To establish wider usage, achieving multicolor and high-resolution characteristics is indispensable. In this paper, we demonstrated that the introduction of substituents such as methyl groups into bipyridine units changed the stereostructure of the cation radicals, and thus shifted the color (e.g., ordinary purple to blue). Also, by relaxing excessive π-stacking between the viologen moieties, the response rate was improved by a factor of more than 10. The controlled charge transport throughout the polyviologen layer gave rise to the fabrication of EC displays which are potentially suitable for the thin film transistor (TFT) substrate as the counter electrodes with submillimeter pixels. The findings can be versatilely used for the new design of polyviologens with enhanced electrochemical properties and high-resolution, multicolor EC displays.
Highlights
Redox-active polymers have been attracting considerable attention as the key components of various energy-related devices such as charge storage devices, displays, memories, and solar cells due to their splendid electrochemical characteristics [1,2,3,4,5,6,7,8,9]
Polyviologen consist of reported as an electrochromic material which was transparent in a dication state and reddish reported as andimethyl-substituted electrochromic material which was in a dication state and reddish purple in normal1 and bipyridine unitstransparent as redox centers, respectively
Density functional theory (DFT) calculation showed that the twist angle of bipyridine in the radical cation state was increased by
Summary
Redox-active polymers have been attracting considerable attention as the key components of various energy-related devices such as charge storage devices, displays, memories, and solar cells due to their splendid electrochemical characteristics [1,2,3,4,5,6,7,8,9]. The absorption wavelength was tuned by introducing substituent to redox-active units, changing conjugation length, and substitution of heteroatoms or metals in case of polythiophenes and metallopolymers [11,12,13,14,15] Such color tunability and the potentially high reflectance of the EC cells (>70%) [21,22] could be regarded as one of the important advantages against conventional electronic papers (e-papers) [23,24,25]. Of EC a significant alternative to the conventional configuration of EC displays, a new simple electrodes pixel size was centimeter scale in the reported device [33]). Sub-millimeter pixels realized without etching the reflectance light beyond was achieved forpixels electrochromic cells due to without the smaller loss of stray loss loss of stray light in the device. Schematics for electrochromic displays installed with thin film transistor substrates for displays installed with thin filmfilm transistor substrates and and
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