Development of sol–gel redox I3−/I− electrolytes and their application in hybrid electrochromic devices

A sol–gel organic–inorganic hybrid was used as a network former for the incorporation of the I3−/I− redox couple and employed as a redox electrolyte in a hybrid electrochromic (EC) device. The electrochromic properties and the stability of EC hybrid devices were tested up to 1800 cycles. To diminish the crystallization of KI established from SEM and EDX measurements, various co-solvents with high boiling points (butanediol, propanediol, sulfolane, propylene carbonate, ethyl acetate and acetonitrile) were incorporated in gels. Structural studies were performed with different spectroscopic techniques, including UV–visible, impedance, in-situ IR and in-situ resonance micro Raman spectroscopic techniques. The results revealed that, for obtaining a high electrochromic effect, I− and I3− ions must be properly balanced. Studies made on the electrochemically degraded redox electrolytes showed conformational changes of the PPG chains, which constituted the sol–gel hybrid matrix and the formation of KI microcrystallites.