Temperature‐Dependent Voltage Control of Flexible Polymeric Electrochromic Devices for Improved Durability

Abstract The thermal stability of polymeric electrochromic devices (ECDs) on flexible substrates is crucial for most applications. In this study, the high‐temperature cycling stability of the side‐chain modified poly(3,4‐ethylenedioxythiophene) (PEDOT‐EthC6) and Prussian blue (PB) ECDs on indium tin oxide coated polyethylene terephthalate (PET‐ITO) is investigated up to 60 °C. Without a temperature‐dependent voltage control, a loss of optical contrast of 21% over 10 000 cycles at 60 °C and ±1.1 V is observed. Analysis of the cycled ECDs and cyclic voltammetry of the electrodes reveal that side reactions of the EC materials occur during cycling. A local aggregation state of the PEDOT‐EthC6 is degraded. The PB electrode is overoxidized toward Prussian green as confirmed by UV‐vis spectroscopy. Raman spectroscopy shows an altered doping state of the PEDOT‐EthC6 electrode after cyclic voltammetry measurements up to 80 °C. The temperature‐dependent onset potentials of the side reactions are determined. By cyclic voltammetry of ECDs with a Li reference electrode, safe voltage windows are established. With −0.55 V / +1.1 V, 91% of the initial contrast of τ_v = 10% ↔ 65% is retained over 10 000 cycles at 60 °C. The results demonstrate that an adaptation of switching parameters for temperature can improve the thermal stability of polymeric ECDs.