Totally organic polymer-based electrochromic cell using TEMPO-substituted polynorbornene as a counter electrode-active material

An electrochromic (EC) cell using a viologen-based polymer as an EC material and a radical polymer bearing a redox-active 2,2,6,6- tetramethylpiperidin-N-oxyl (TEMPO) group per repeating unit as a counter electroactive material was fabricated. The radical polymer was spin-coated on an ITO/glass electrode as the counter electrode of the EC cell. The electrochromic material of the cell was a polyion complex consisted of poly(decyl viologen) and poly(styrene sulfonate) (PVlO-PSS), which was also spin-coated on the ITO/glass. An ion-conducting polymer gel solution was sandwiched between the two electrodes. Electrochemical switching of the cell was monitored using the visible absorption of the PV10-PSS complex (λ_max = 550 nm) that appeared in the reduced state, while the radical polymer was transparent in the visible region in both redox states. PVlOPSS and the radical polymer were concurrently reduced and oxidized, respectively, on each electrode during the charging process, which corresponded to the coloration of the cell. The decoloration of the polyion complex was effected by a discharging process under short circuit conditions. The electrochromic behavior of the cell was characterized by a remarkably low driving voltage, as a result of a small potential gap between PV10-PSS and the radical polymer. The use of the organic redox polymers, not only for the low energy-driven electrochromic switching but also for the charge-storage purposes, allowed a universal design of a battery-like display device, with possible application to a flexible and totally organic electrochromic cell.