Control of morphology and performance of diketopyrrolopyrrole-based electrochromic polymers using solvent vapor annealing
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Post-deposition treatment including thermal and solvent annealing of polymer films in various organic electronics such as organic photovoltaics and organic thin film transistors plays a vital role in governing the film morphology and consequently their optical and electronic properties. However, such a post-treatment method has yet been used for electrochromics. This paper studied the influence of solvent vapor annealing of a diketopyrrolopyrrole-containing electrochromic conjugated polymer on its film morphology. Compared to an un-annealed film, the films exposed to acetone vapor and chloroform vapor are generally composed of polymer clusters with smaller domain sizes and more compact, aggregated structures. Subsequent evaluation of the electrochromic performances of the devices revealed the strong influence of the film morphologies on the optical contrasts, switching times and coloration efficiencies. In general, the electrochromic films treated with a poor solvent (acetone) exhibited faster switching speeds and improved coloration efficiencies. In contrast, treatment with a good solvent (chloroform) had destructive effects on the optical contrasts, switching speeds and coloration efficiency of the films. These findings showed that the electrochromic performance closely corresponded to changes in the film structure and morphology.
KeywordsConjugated polymers Electrochromism Electrochromic device Solvent vapor annealing Morphology
This research was supported by the Agency for Science, Technology and Research (A*STAR) and Ministry of National Development (MND) Green Building Joint Grant (No. 1321760011).
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