Effect of Deposition Conditions on the Electrochromic Properties of Nanostructured Thin Films of Ammonium Intercalated Vanadium Pentoxide Xerogel

We have examined the influence of the deposition temperature and deposition time on the electrochromic activity of nanostructured (NH4)(0.3)V2O5 center dot 1.25H(2)O thin films prepared by the newly developed chemical bath deposition method. The film structure is characterized by XRD powder diffraction, IR spectroscopy, and TG-DTA techniques. SEM and AFM observations evidence that the common ribbon-like structure is modified by the different deposition conditions mainly with respect to the particle sizes, ribbons orientation, and films porosity. The electrochemical and electrochromic properties of two series of thin films prepared at 50 and 85 degrees C for different deposition time are studied. All films exhibit two-step electrochromism with color changes yellow/green and green/blue, related to the stepwise reduction/oxidation processes between V(V) and V(IV) sites. The electrochromic changes are stable after prolonged film storage and for at least a hundred cycles. The optical properties of (NH4)(0.3)V2O5 center dot 1.25H(2)O thin films are found to depend significantly on the deposition conditions as the higher deposition temperature is favorable in providing higher values of the transmittance variance. The best result achieved for the transmittance variance of 55% at 400 and 900 nm clearly demonstrates the potential of ammonium intercalated vanadium oxide xerogel thin films for commercial application in electrochromic devices.