Electrochromic Nanostructured Tungsten Oxide Films by Sol-gel: Structure and Intercalation Properties

Publisher Website
Google Scholar
Abstract
As-deposited sol-gel derived amorphous tungsten oxide films transform into nanostructured films with an interconnected framework of grains and pores and a dominant triclinic crystalline phase upon annealing at 250°C250°C . Transmission electron microscopy and scanning electron microscopy images clearly reveal the annealing-induced microstructural evolution for the film. Subsequent to lithium intercalation, the film annealed at 250°C250°C shows quasi-reversible structural changes, as ascertained by X-ray diffraction and Fourier transform infrared spectral data. Dynamic transmission modulation for film revealed a high optical modulation of 72% (λ=650nm)(λ=650nm) and a coloration efficiency maximum of 132cm2C−1132cm2C−1 at 800nm800nm under a lithium intercalation level of x=0.20x=0.20 . X-ray photoelectron spectroscopy of the W 4f core levels demonstrated a progressive increase in the W5+W5+ content at the expense of W6+W6+ proportion as the insertion coefficient was raised from 0 to 0.25, with 0.20 as the threshold value above which the W5+W5+ content exceeds the W6+W6+ proportion. A new W4+W4+ state also appears which acts to lower the coloration efficiency for x⩾0.22x⩾0.22 . The presence of charged oxygen interstitials in the vicinity of electrochemically active tungsten sites is also responsible for the coloration efficiency decline at high ion insertion levels.