Spectroscopic and electrochromic properties of activated reactive evaporated nano-crystalline V 2 O 5 thin films grown on flexible substrates

Vanadium pentoxide (V2O5) thin films were grown on indium tin oxide-coated flexible Kapton substrates by homebuilt activated reactive evaporation technique. Film depositions were carried out at optimised oxygen partial pressure of 1×10-3 Torr and plasma power of 8 W, and we investigated their microstructural and optoelectrochromic properties as a function of substrate temperature. The V2O5 films grown at Ts=473 K exhibited a nano-crystalline nature as evidenced from X-ray diffraction, atomic force microscopy and Raman studies. The nanocrystalline films composed of vertical elliptical-shaped grainy morphology demonstrated a high optical transmittance of 75% with an estimated optical bandgap of 2.38 eV. The dry lithiated nano-crystalline V2O5 films demonstrated an optical modulation of 36.1% with a coloration efficiency value of 26.2 cm2/C at a wavelength of 550 nm. As-deposited nano-crystalline V2O5 thin films demonstrated a constant discharge capacity of about 60 mAh cm-2 mm-1 for a few cycles at room temperature in the potential window of 4.0 to 2.5 V.