(98%, Sigma Aldrich), Sodium borohydride (NaBH$_4$, Alfa Aesar), and Acetonitrile (ACN, anhydrous, 99.8%, Sigma Aldrich) were used as received. Active material used for fabricating electrochromic devices was prepared in the solution form by mixing 4 wt.% ethyl viologen diperchlorate \[EV (ClO$_4$)$_2$\] in acetonitrile and 5 wt.% PEO in acetonitrile. The PEO solution was filtered through a 0.45 $\mu$m PTFE filter before adding the viologen solution. The solution (PEO+EV) has been deposited over the electrode by dropping 3 $\mu$l of solution in such a way that the drop centers on the E$_1$-E$_2$ gap in the OFG (Fig. S1 in SI) and then dried the film in vacuum.

Cross-bar geometry (CBG) device has been fabricated by placing a film of EV+PEO between two transparent conducting electrodes of ITO deposited on quartz substrate using magnetron sputtering deposition \[25\]. The EV+PEO film was obtained on an ITO coated substrate using spin coating. After spin coating, second ITO electrode was laminated face to face on the spin coated substrate. The extreme part of both the electrodes was painted by silver glue for making connection with external power supply. UV-Vis spectroscopy was performed using Cary 60 UV-Vis spectrophotometer of Agilent whereas Raman spectroscopy was done using 