Factors Impacting the Photostability of a Roll‐to‐Roll Processed PEDOT Derivative for Flexible Electrochromic Devices

For the use of polymeric electrochromic devices (ECDs) in architectural or automotive applications, the photostability of the electrochromic (EC) polymer is crucial for long-term durability. In this study, the photostability of the side-chain modified poly(3,4-ethylenedioxythiophene) (PEDOT-EthC6)thin films deposited by roll-to-roll slot-die coating on indium tin oxide coated polyethylene terephtalate (PET-ITO) is investigated and characterized by UV-vis and IR spectroscopy. Residual iron salt on the EC polymer layer, necessary for the in situ polymerization, and the variation of storage times between processing steps have no influence on the degradation rate during light exposure. The photostability of the thin films is 30% better in an inert atmosphere than in ambient conditions. Different long-pass filters are applied to enhance the photostability in the colored and the bleached state. The position of the absorption edge strongly affects the photostability and visual appearance/color of the PEDOT-EthC6 electrodes. The analysis of the CIE L*a*b* color coordinates reveals that a trade-off between stability and a desirable color is necessary. To prevent UV degradation of the EC polymer in flexible ECDs, sputtered nickel oxide is chosen as the counter electrode material. The hybrid ECD shows no sign of degradation and loss of electrochromic performance after 350 h of light exposure.