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

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°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°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% ͑ = 650 nm͒ and a coloration efficiency maximum of 132 cm 2 C −1 at 800 nm under a lithium intercalation level of x = 0.20. X-ray photoelectron spectroscopy of the W 4f core levels demonstrated a progressive increase in the W 5+ content at the expense of W 6+ proportion as the insertion coefficient was raised from 0 to 0.25, with 0.20 as the threshold value above which the W 5+ content exceeds the W 6+ proportion. A new W 4+ state also appears which acts to lower the coloration efficiency for x ജ 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.

Mesoporous amorphous tungsten oxide electrochromic films: a Raman analysis of their good switching behavior

“…This spectrum resembles to a great extent with the ones reported for lithiated tungsten oxide films at the initial steps of crystallization [11,36]. From these references, such a spectrum derives from Li x WO 3 crystallites (see also dark-field TEM micrograph S4).…”

Electrochromic Response of Nanostructured Poly(3,4‐ethylenedioxythiophene) Films Grown in an Aqueous Micellar Solution

“…[28] For PEDOT electropolymerized from a bicontinous microemulsion, the dopant levels calculated from synthesis potential and polymerization charge passed ranged between 0.09 and 0.16. [22] Authors concluded that a higher dopant content in the polymer led to an enhanced redox activity and the effect of a high doping level as observed in this study on the redox behavior can be seen in the following discussion. In doped PEDOT, different charge carrying moieties prevail such as polarons, [29] which carry a magnetic moment and, therefore, these can also be observed by EPR.…”

“…[18] Both high ionic (triflate) and micelle (SDS) content in the precursor electrolyte result in a greater number of aggregates formed and larger micellar size, as compared to what can be obtained in a traditional organic electrolyte. [18,22] In addition, the swelling of the micelles upon monomer incorporation, may also act to increase the size of globules formed. But a better control over surfactant concentration in the deposition bath may probably ensue in a still narrower range of globule size in the film and this will lead to a more ordered arrangement of grains and pores and enable a more efficient doping-dedoping process.…”

Efficient electrochromic device based on sol–gel prepared WO3 films

“…It should be pointed that its peaks become sharper and more intense with the increasing of annealing temperature. The structural parameters are well along with PDF card number 20-1323, indicating that the films are of crystalline triclinic structure [15]. It is well known that the EC performance of WO 3 is closely related to its level of crystallization [22].…”

“…With regard to low-cost and convenient processes for the large-scale preparation, it is preferable to prepare WO 3 film by sol-gel technology [14][15][16][17][18]. Although there are lots of works focused on the high efficient EC performance of WO 3 films, few interests and researches have been devoted to assembled EC device.…”