Electron Donor Ferrocenyl Phenothiazine: Counter Ion for Improving All-Organic Electrochromism

Abstract

Electron-donating properties of 3-ferrocenylethynyl-10-propyl-10H-phenothiazine (FPP) has been studied to be used as an efficient counter ion for application in a viologen-based organic electrochromic device to facilitate an efficient all-organic electrochromic device. The FPP molecule, when used as a counter ion with viologen, improves the switching time to less than half a second and exhibits lower operation voltage of ∼1 V and excellent stability for longer than 1800 s with a negligible amount of absorption loss. Spectroscopic and electrochemical measurement techniques have been used to understand the mechanism of bias-induced enhanced performance of the FPP-viologen-based solid-state electrochromic device. The device does not contain any liquid electrolytic medium to support its switching behavior and can also be fabricated on a plastic substrate for realization of a flexible all-organic electrochromic device. The viologen-FPP electrochromic device showed an optical contrast of more than 55% with a bias of 0 to 1 V when switched between OFF- (transparent) and ON- (blue) states. An excellent value of coloration efficiency of 460 cm2/C is obtained with a simple all-solid device geometry arrangement, making it the most efficient solid-state electrochromic device in the viologen family of devices. © 2020 American Chemical Society.