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Optical Absorption and Durability of Sputtered Amorphous Tungsten Oxide Films
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.ORCID iD: 0000-0002-8279-5163
2003 (English)In: Solid State Ionics, ISSN 0167-2738, E-ISSN 1872-7689, Vol. 165, no 1-4, 51-58 p.Article in journal (Refereed) Published
Abstract [en]

Amorphous tungsten oxide films were made by sputtering onto glass substrates that were coated with conductive tin doped indium oxide (ITO). The films were deposited at different O2/Ar gas flow ratios and different substoichiometric compositions was determined by Elastic recoil detection analysis (ERDA). Substoichiometric as-deposited tungsten oxide is transparent above a particular oxygen content and is blue below that content. This indicates that there are at least two kinds of defects in the substoichiometric films. The oxygen vacancies may be coupled to W5+ sites, giving rise to strong absorption, or to (W–W)10+ complexes in the transparent films. Lithium ions were electrochemically intercalated at several charge levels. At each level the transmittance and reflectance were measured in the wavelength range between 0.3 and 2.5 μm. We show that as-deposited blue films and intercalated transparent films display similarly shaped optical absorption bands. Electrochromic devices were made by laminating the tungsten oxide films with sputtered Ni–V oxide deposited on ITO-coated plastic substrates. The durability under electrochemical cycling was best for the case of very substoichiometric WO2.63 films.

Place, publisher, year, edition, pages
2003. Vol. 165, no 1-4, 51-58 p.
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:uu:diva-92423DOI: 10.1016/j.ssi.2003.08.016OAI: oai:DiVA.org:uu-92423DiVA: diva2:165493
Conference
Fifth International Meeting on Electrochromism
Available from: 2004-11-12 Created: 2004-11-12 Last updated: 2015-09-14Bibliographically approved
In thesis
1. Optical Absorption and Electrical Conductivity in Lithium Intercalated Amorphous Tungsten Oxide Films
Open this publication in new window or tab >>Optical Absorption and Electrical Conductivity in Lithium Intercalated Amorphous Tungsten Oxide Films
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Optical and electrical properties of electrochemically lithium ion intercalated thin films of x-ray amorphous tungsten oxide made by magnetron sputtering on glass substrates coated with a thin layer of conductive tin doped indium oxide, have been studied.

The composition and the density of the films were characterized by the ion beam analysis methods Rutherford Backscattering Spectroscopy and Elastic Recoil Detection Analysis.

The optical properties, transmittance and reflectance were investigated by spectophotometry in the wavelength range 300-2500 nm. The absorption coefficients were calculated at different lithium intercalation levels.

It was found that the absorption coefficient in an as-deposited blue film has a similar asymmetric shape as for films intercalated to a Li/W ratio of ~0.03. It was possible to electrochemically bleach this film to transparency. Stoichiometric films show optical irreversibility between the bleached and the colored state in the first cycle.

A polaron absorption model has been compared to the absorption coefficient for films of different intercalation levels. An increase in the Fermi level and in the polaron band width, and a nearly constant activation energy was found as the Li/W value increased. The radius of the polaron wavefunction for different lithium intercalation levels and film compositions has been estimated from electrical measurements.

The total absorption coefficient has been compared to the site-saturation model. The model is good for films intercalated in the optically reversible region. A modified site-saturation model that could be applied also in the optically irreversible region and involves electron transitions between W6+, W5+ and W4+ sites, has also been compared to experimental values.

It was found that the total absorption, optical density and the coloration efficiency is higher for the WO2.63 film than in the less oxygen deficient films and that this film is optically more durable in an electrochemically cyclic lifetime device test.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2004. 73 p.
Series
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 1045
Keyword
Technology, Lithium intercalation, amorphous, tungsten-oxide, sputtered films, optical absorption, polaron radius., TEKNIKVETENSKAP
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-4687 (URN)91-554-6106-9 (ISBN)
Public defence
2004-12-03, Polhemssalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2004-11-12 Created: 2004-11-12 Last updated: 2009-03-27Bibliographically approved

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Niklasson, Gunnar A.

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