Influence of the Nb2O5 doping on the electrochemical properties of V2O5 thin films

Abstract

Aiming to improve electrochromic properties of vanadium pentoxide (V2O5) new niobium-doped vanadium pentoxide (V2O5:Nb2O5) thin films were obtained by combining sol–gel method with dip-coating technique. The sols were synthesized by reacting vanadium (V) oxytripropoxide and niobium ethoxide (V) with 2, 5, and 10mol% of Nb sol concentrations as precursors. The films were deposited on a FTO conducting glass substrates and heat treated at 300°C. Cyclic voltammetry characterization of V2O5 and V2O5:Nb2O5 films revealed two cathodic and two anodic peaks that fused in one with increase of scan rate up to 50mV/s. Chronoamperometry showed that the doped samples are more stable than undoped ones. Chronocoulometry measurements proved that the best values of charge density of about 80 mC/cm2 was obtained for the film doped with 5mol% of Nb sol. UV–Vis spectroscopy confirmed 47% transmittance difference at 633nm between colored and bleached states of doped sample, which was 6% more than for undoped one. The characterization of the Nb intercalated V2O5 deposits was done combining energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD), proving a possibility of synthesis of structured niobium intercalated vanadium oxides. Moreover, scanning electron microscopy (SEM) morphology and atomic force microscopy (AFM) topography analyses evidenced uniform and smooth surface of the films with more granules on the surface of the doped sample and the RMS values of 9.66 and 3.45nm for V2O5:Nb2O5 and V2O5 film, respectively. V2O5:Nb2O5 electrochromic films have shown improved electrochemical stability and transmittance difference between colored and bleached values, when compared to pure vanadia films.