%0 Journal Article
%A Nilgün Özer
%A Timothy Barreto
%A Temel Buyuklimanl
%A Carl M Lampert
%B Solar Energy Materials and Solar Cells
%D 1994
%G eng
%L LBL-38525
%P 433-443
%T Characterization of Sol-Gel Deposited Niobium Pentoxide Films for Electrochromic Devices
%V 36
%1 <p>Windows and Daylighting Group</p>
%2 LBL-38525
%X <p>Niobium pentoxide films, fabricated by the sol-gel process, were spin coated onto conductive indium tin oxide (ITO)/glass, and microscope slides. These films were cycled in a 1M LiClO<sub>4</sub> propylene carbonate (PC) solution, and exhibited electrochromic behavior upon the electrochemical insertion (reduction) and extraction (oxidation) of lithium. In-situ optical transmittance measurements were investigated in the ultraviolet/visible/near-infrared wavelength regions (250-2100 nm). Niobium pentoxide films showed reversible optical switching from 320 to 870 nm, but were found electrochromically inactive in the infrared region. Surface analysis using X-ray photoelectron spectroscopy (XPS) indicated little difference in the chemistry of Nb<sub>2</sub>O<sub>5</sub> films as deposited and lithiated Li<sub>x</sub>Nb<sub>2</sub>O<sub>5</sub> films, as XPS binding energies of Nb and O showed no appreciable shifts. These films were found to be amorphous by X-ray diffraction. Optical transmittance measurements combined with cyclic voltamograms and XPS spectra, revealed that the electrochromic behavior of these films occurs due to the insertion of Li<sup>+</sup> cations into niobium pentoxide films. The bronze coloration of the niobium pentoxide films could make them useful as an electrochromic counter electrodesfor electrochromic devices.</p>