Enhancing the Spectroelectrochemical Performance of WO3 Films by Use of Structure-Directing Agents during Film Growth

Abstract

Thin, porous films of WO3 were fabricated by solution-based synthesis via spin-coating using polyethylene glycol (PEG), a block copolymer (PIB50-b-PEO45), or a combination of PEG and PIB50-b-PEO45 as structure-directing agents. The influence of the polymers on the composition and porosity of WO3 was investigated by microwave plasma atomic emission spectroscopy, energy-dispersive X-ray spectroscopy, scanning electron microscopy, X-ray diffraction, and gas sorption analysis. The electrochromic performance of the WO3 thin films was characterized with LiClO4 in propylene carbonate as electrolyte. To analyze the intercalation of the Li+ ions, time-of-flight secondary ion mass spectrometry, and X-ray photoelectron spectroscopy were performed on films in a pristine or reduced state. The use of PEG led to networks of micropores allowing fast reversible electrochromic switching with a high modulation of the optical transmittance and a high coloration efficiency. The use of PIB50-b-PEO45 provided isolated spherical mesopores leading to an electrochromic performance similar to compact WO3, only. Optimum characteristics were obtained in films which had been prepared in the presence of both, PEG and PIB50-b-PEO45, since WO3 films with mesopores were obtained that were interconnected by a microporous network and showed a clear progress in electrochromic switching beyond compact or microporous WO3.

Effect of metal dopants on the electrochromic performance of hydrothermally-prepared tungsten oxide materials

“…38 The transmittance change percentage (DT%) at a given specic wavelength of 560, 630 and 710 nm can be calculated using eqn (2). 25,39,40 As observed in Fig. 6 and Table 2, the DT% values increase with wavelength.…”

“…The colouration efficiency (CE) of all sample is calculated from the change in optical contrast density (ΔOD) per the total charge that passes across the unit area of the thin film electrode ( Q d , C cm −2 ) as shown in eqn (3) and (4) . 25 CE = ΔOD/ Q d where ΔOD( λ ) = log( T bleached( λ ) / T coloured( λ ) ) Q d is the amount of charge that is inserted into the thin film which can be determined by integrating the curve area of current density versus time.…”

Ultrathin Al2O3 Protective Layer to Stabilize the Electrochromic Switching Performance of Amorphous WOx Thin Films

“…These include wet chemical synthesis methods as well as gas-phase techniques. [29][30][31][32][33][34][35][36][37][38] Depending on synthesis method and preparation parameters, the composition, crystal structure or morphology can be specifically adjusted to ensure proper function for the desired application. In terms of composition, sputter-deposited samples of nearstoichiometric tungsten oxide have a lower coloration efficiency than sub-stoichiometric tungsten oxide (WO x , x < 3).…”