Design of highly stable and solution-processable electrochromic devices based on PEDOT:PSS

This study aimed to improve the repeatability of electrochromic devices(ECD) based on Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)(PEDOT:PSS); therefore, ferrocene was introduced as an anodic species. When 0.05 wt% ferrocene as compared to that of the electrolyte was contained in the electrolyte layer, the bleaching time significantly reduced from 110 s to 25 s without changing ΔT; consequently, repeatability markedly improved. However, ferrocenium cations, generated when ferrocene undergoes a reversible redox reaction, have high reactivity with oxygen, and hence, the stability of ECD is lowered over time. To overcome this problem, l-ascorbic acid, commonly known as vitamin C, was introduced as an antioxidant in the electrolyte layer. The repeatability of the ECD and the storage stability of the electrolyte solution were improved without side effects at an l-ascorbic acid ratio of 0.025 wt% as compared to that of the electrolyte. In addition, using cyclic voltammetry, it was confirmed that l-ascorbic acid did not affect the electrochemical properties of the ECD, and played only the role of an antioxidant for ferrocene. Furthermore, regarding encapsulated ECD, high repeatability could be maintained by preventing solvent evaporation and oxygen penetration into the electrolyte layer. When ECD of size 4 cm × 5 cm was glass encapsulated, there was no change in ΔT even after 5000 cycles for 139 h. We observed day-to-day changes in the response time and ΔT for 30 d; it maintained almost constant values from the beginning. Repeatability tests of 15 cm × 15 cm size large-area ECD for applications, such as smart windows, were conducted.