Poly(3,4-ethylenedioxythiophene) and Viologen Based Materials for Electrochromic Devices

Sydam, R (2015) Poly(3,4-ethylenedioxythiophene) and Viologen Based Materials for Electrochromic Devices. PhD thesis, Indian Institute of Technology Hyderabad.

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Abstract

Electroactive materials which undergo reversible optical changes through electrochemical redox reactions by the application of an electric field are called electrochromic (EC) materials. Among various electrochromes, organic electrochromes such as poly(3,4-ethylenedioxythiophene) (PEDOT) and viologens can modulate visible light and offer high contrast ratios and fast switching times. In the present thesis, PEDOT/fulleropyrrolidine films were prepared for the first time and the optical response of the film is completely altered by the presence of the fullerene derivative; a coloration efficiency of 386 cm2 C-1 was acheived. Electrohromic devicves (ECDs) with a PEDOT film as cathode and a Prussian blue (PB) film as anode were constructured and the superior EC performance of the an in-situ polymerized ionic liquid based gel electrolyte compared to a conventional gel electrolyte was demonstrated. The optimized in-situ polymerized gel was then used in a heptyl viologen based ECD and the switching of a large area device (8 cm  6 cm) for antiglare electrochromic rearview (ECRA) mirrors was demonstrated. PEDOT films were then transposed over plastic substrates and their ability to serve as a transparent conductor and an electrochromic electrode was shown. Similarly viologens offer different colors depending on the N-substituent. Although a variety of viologens were synthesized in the past, a reversible and high write-erase efficiency continues to pose a formidable challenge. To address this concern, new derivatives of viologens were synthesized by the use of substituents like butylbenzimidazole and ethylindole, their ECDs were constructed and characterized. Further, a hybrid viologen was also prepared by using a phosphonitrillic trimer (P3N3Cl6) as a central core and the potential of this viologen for durable, high contrast ECDs was shown. These viologen based ECDs showed very high contrast ratios, high coloration efficiencies, short response times and the devices can endure more than 2000 cycles without undergoing degradation. These devices and materials are very much useful for applications such as flexible displays, energy saving switchable windows in buildings and automobiles and ECRA mirrors.

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