Live spectroscopy to observe electrochromism in viologen based solid state device

Abstract

In-situ Raman and UV–vis spectroscopies have been carried out from viologen based electrochromic device fabricated in two simple geometries. Ethyl viologen diperchlorate in polyethylene oxide matrix was used as the active layer in the device without any counter material to understand the effect of bias on viologen. The device, which is transparent otherwise, changes its color to navy blue when a bias of 2 V is applied. Reduction of viologen to its free radical state as revealed from Raman spectroscopy recorded in-situ in both the geometries appears to be the mechanism for this color switching. It is also observed that absorbance of the device is perturbed when bias is applied with maximum change in absorbance corresponding to green wavelength which is giving the blue tint of the device in on state. We establish that UV–vis and Raman spectroscopies prove to be the best method for understanding the mechanism of color switching in viologen based electrochromic device because it gives the advantage to see a device ‘live’ while operating. © 2017 Elsevier Ltd