Studies on All-Solid Electrochromic Devices Fabricated by a Bilayered Assembly of Hydrated Vanadium Pentoxide and PEDOT:PSS Coatings

Vanadium pentoxide (V2O5) based electrochromic devices (ECD) are notable for electropolychromism owing to their adjacent multiple oxidation states in the energy space. V2O5 also exhibits high theoretical capacitance, therefore have excellent potential to be utilized in various multifunctional devices; although these devices suffer from poor electrochemical stability. Herein, we report electrodes fabricated by overcoating hydrated-V2O5 (HVO) films with a thin layer of PEDOT:PSS. The ECDs with lower thickness HVO coatings showed multiple color switching representing V5+(orange/yellow), intermediate (green) and V4+ (blue) states while only partial reduction of V5+ ⇔ intermediate states (V4++V5+) could be obtained for the uncoated HVO. In addition, we observed almost no degradations for the cyclic stabilities of bilayered devices (measured for 1000 cycles) compared to a huge ~70% transmittance contrast compromise for bare HVOs. ECDs with higher thickness (~450 nm and above) V2O5 coatings offered improved color intensities and ~44% contrast retention. The differences in the electrochemical response was investigated by impedance studies that revealed a decoupling of the responses between the individual layers for the higher thickness variant.