Photoelectrochromic performance of tungsten oxide based devices with PEG–titanium complex as solvent-free electrolytes

Photoelectrochromic (PEC) devices were assembled with an electrochemically deposited tungsten oxide (WO3) thin film on transparent conductive glass (ITO) substrates, a composite polymeric electrolyte (PE), and a Ruthenium 535 sensitized TiO2 sol–gel film deposited on ITO substrates. The polymeric electrolyte was prepared by the sol–gel method using a viscous polyethylene glycol (PEG, MW 600) and titanium isopropoxide as precursors in an acidic medium. A lithium salt (LiI) was added to the PEG–Ti complex for photoelectrochemical purposes. The color change of WO3 based PEC devices under 100 mW/cm2 illumination at short circuit conditions indicates that the introduction of titanium complex inside the polymeric electrolyte accelerates the coloring speed from 26 to 9 s. Electrochemical impedance spectroscopy analyses of PEC devices show that the presence of titanium complex in PE reduces the charge transfer resistance and increases the charge storage capacity of the cells. This improvement could come from the oxidation of iodides and reduction of titanium ions inside the composite electrolytes that increase the lithium ionʹs mobility.