Crystallized V₂O₅ as Oxidized Phase for Unexpected Multicolor Electrochromism in V₂O₃ Thick Film

Our e-connected society is eager to develop devices with tunable colors. Electrochromic materials, able to modify their optical properties under an applied voltage, offer a smart solution. In the present study, we have successfully synthesized two vanadium oxide powders from a polyol-mediated synthesis, and powder suspensions were coated on glass/ITO substrates by doctor blading. The electrochemical and optical properties of the V_<i>x</i>O_<i>y</i> films are investigated by cyclic voltammetry (CV) coupled with in situ UV–visible spectroscopy. Both V₂O₅ and V₂O₃ films exhibit reasonably good cycling stability, significant reflectance modulation, high optical contrast, and good memory effects revealing the unknown EC properties of V₂O₃. The similar green ⇄ blue ⇄ orange reversible color changes for both vanadium oxides appear suitable for display application. Then, the evolution of the vanadium cation oxidation states and of the structure of V₂O₅ and V₂O₃ upon cycling are analyzed by ex situ XPS and ex situ XRD (at grazing incident angle). This work highlights a robust and novel scenario upon cycling, nearly the same whatever the raw film composition that shows, for each cycle, the crystallization of V₂O₅ upon oxidation, followed by amorphization upon reduction