A review on the prominence of porosity in tungsten oxide thin films for electrochromism

Gupta, Jyothi; Shaik, Habibuddin; Kumar, Kiran

doi:10.1007/s11581-021-04035-8

Cited by 41 publications

(12 citation statements)

References 181 publications

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“…Precursor solutions based on tungsten hexachloride [17,18], peroxotungstic acid [14,19], sodium tungstate [16,20] or ammonium metatungstate [21] have been used successfully for the preparation of tungsten oxide thin films. Further, the internal structure of WO 3 can be tuned in a wide range using such solution-based approach [22,23].…”

Section: Introductionmentioning

confidence: 99%

“…The addition of polymers or surfactants as structure-directing agents into the precursor solution allows a facile modification of the porosity and atomic arrangement (amorphous vs. crystalline) of the WO 3 films [22,23]. Polyethylene glycol (PEG) of different molecular weight has been largely used in sol-gel processes to inhibit crystallization of WO 3 [22,24].…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2022

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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.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

et al. 2022

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“…These values are ∼10 s larger compared to conventional EC materials but are reasonable for applications of static display and color-appearance modulations . This is because the inherent low porosity of the ALD film and the use of an aqueous electrolyte solution exert a high barrier for ion diffusion from the electrolyte to the ALD film . The cyclic durability was evaluated by switching the electrode potential between 0.5 and 2.8 V repeatedly (Figure d).…”

Section: Resultsmentioning

confidence: 99%

“…Previous literature suggests that the grain boundary is the ion migration channel for the polycrystalline ALD film , because nanocrystals are atomically dense and hard to penetrate. Faster switching time can be potentially acquired by using a porous template for ALD film growth, , which can improve the ion transport and the EC reaction kinetics . Using this method, nanoporous or mesoporous structures can be fabricated based on a selected ALD growth template to control the porosity of the film. − For EC applications, these structures may help increase the contact area between the solid/liquid interface, providing facile ion transport channels.…”

Section: Resultsmentioning

confidence: 99%

Multicolor Bipolar Modulation of Titanium–Chromium Oxide Electrochromic Coatings

Shen

Yang

ChengXing

et al. 2023

ACS Appl. Electron. Mater.

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Electrochromic (EC) materials offer wide-ranging commercial applications, including smart windows, electrochromic mirrors, and programmable static displays. While many conventional electrochromic applications require the encapsulation of the EC materials and other components inside a sealed cell, there are cases where the color appearance of the object’s surface needs to be durable in atmospheric or aquatic environments. Among the current fabrication methods for EC materials, atomic layer deposition (ALD) remains less explored. In this work, we fill these gaps by employing ALD to grow a (Ti,Cr)O x film as a new subset of EC coatings that operates in direct contact with aqueous solutions. The protective and bipolar coloration properties of the (Ti,Cr)O x are achieved by the ALD alloying of TiO2 and CrO x nanocrystals. Intrinsic EC performance showed excellent cycle stability of more than 2000 cycles in aqueous electrolytes of high salinity and high corrosion resistance in pH = 0 acid. Furthermore, multicolor modulation has been achieved via a Fabry–Perot optical cavity design. Microstructural and spectroscopic characterizations combined with finite-difference time-domain (FDTD) modeling allow us to correlate the optical appearance with coating electronic and microstructures. This work showed that this ALD-grown ternary EC coating can also act as a surface protection layer and has unique advantages over other EC materials to achieve balanced performance among color tunability, coloration efficiency, and cycle stability.

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“…The general reversible electrochromic behavior is due to the formation of M x WO 3-y , where M corresponds to H, Li, etc., and where metal ion insertion and electron injection result in an intense blue color with low x value due to photoaffected intervalence charge transfer. Extensive studies show that the intercalation-deintercalation-based electrochromic performance depends mainly on the ion intercalation reaction, which itself is determined by the material's crystallinity, doping level and microstructure, among others [13][14][15][16]. Increasing the color tunability of WO 3-y -based electrochromic devices is another key issue, which is of growing interest over the last few years.…”

Section: Introductionmentioning

confidence: 99%

Advantageous optical characteristics of tantalum vanadium oxide as counter electrode in electrochromic devices

et al. 2022

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Smart windows are an important technology in terms of energy saving potential in the building sector due to their ability to control visible light and thermal radiation. The essential component of this type of window glazing is an electrochromic thin film. In addition to the widely established tungsten oxide as the optically active material, in particular the counter electrode offers significant potential for improving the overall device performance. In this study, tantalum vanadium oxide films are prepared by reactive radio-frequency sputtering on fluorine-doped tin oxide substrates and optimized in terms of their spectro-electrochemical properties as ion storage layer. We show that an oxide-based tantalum-vanadium alloy is a promising approach to address the open challenges of pure vanadium pentoxide. The coatings exhibit color neutrality in combination with a high transmittance of up to 80% in the as-prepared state and suitable optical transmittance switching. Additionally, we find both a sufficient stability upon cycling and a suitable charge density of about 35 mC cm−2. Thus, the presented oxide-based alloy offers a beneficial performance as an ion storage layer in electrochromic devices.

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A review on the prominence of porosity in tungsten oxide thin films for electrochromism

Cited by 41 publications

References 181 publications

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

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

Multicolor Bipolar Modulation of Titanium–Chromium Oxide Electrochromic Coatings

Advantageous optical characteristics of tantalum vanadium oxide as counter electrode in electrochromic devices

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