intensive research into the electrochromic properties of viologens. The current research was undertaken to better understand viologen electrochromism and to simplify the device design for realization of a solid-state electrochromic device.

![Scheme 1: Ethyl Viologen molecule](scheme){width="5cm"}

Controlling the often complex stoichiometry of metal oxides is a complication when fabricating electrochromic devices based on these materials\[15,16\]. In addition, many metal oxides lack sufficient transparency for use in a wide range of applications. In contrast, viologen based materials are solution processable and can yield flexible electrochromic devices. In order to achieve an electrochromic response in the solid state, an ionically conducting matrix is required as well as a redox counter-reaction.

Very recently, lithium perchlorate in polyethylene oxide (PEO) has been used successfully as a solid electrolyte for organic electronics in general and thin film transistors in particular \[10\],\[17-–21\]. Ethyl viologen in PEO matrix can be a good choice for making viologen based eletrochromic devices, at least for testing purposes. Ethyl viologen diperchlorate (EV (ClO$_4$)$_2$) can be a good candidate because it contains EV$^{2+}$ which is a good electron acceptor and also contains perchlorate ion which can act as electrolyte. Its solution in an appropriate solvent is transparent and does not absorb visible 