In-situ spectroscopic studies of viologen based electrochromic device

TL;DR

This study investigates the fundamental mechanisms of color change in viologen-based electrochromic devices using in-situ spectroscopic techniques, revealing redox switching as the cause of bias-induced color change and demonstrating effective absorption modulation.

Contribution

It provides detailed in-situ spectroscopic analysis of the color change mechanism in viologen electrochromic devices, establishing the redox switching process as the core cause.

Findings

Bias induces color change via redox switching between viologen dication and radical forms.

Navy blue color results from suppression of complementary color transparency, not increased blue transparency.

Device exhibits good ON/OFF contrast due to effective absorption modulation.

Abstract

Fabrication and operation of simple solid state electrochromic devices using ethyl viologen diperchlorate in a polymer matrix is presented here. In-situ Raman and transmission/absorption studies have been done to establish the origin of bias induced color change, between a transparent and navy blue color, in the electrochromic device. The origin of bias induced color change has been attributed to the bias induced redox switching between its viologen dication and free redicle forms. Fundamental reason behind colour changes of viologen molecule has been established. In-situ UV-Vis spectra reveals that the navy blue color of the device under biased condition is not due to increase in the transparency corresponding to blue wavelength but due to suppression of the transparency corresponding to the complementary colors. Absorption modulation has been reported from the device with good ON/OFF contrast of the device.