Structural evolution and chemical bonds in electrochromic WO 3 films during electrochemical cycles

Chun Kai Wang, D. R. Sahu, Sheng Chang Wang, Chung Kwei Lin, Jow Lay Huang

Research output: Contribution to journalArticle

20 Citations (Scopus)

Abstract

Electrochromic WO 3 films are prepared by the electron-beam evaporation method. The as-deposited films are amorphous in structure. The optical transmittance spectra show 13.4% decay of optical modulation after 20 electrochemical cycles. The degradation behaviour of the WO 3 films is also observed in electrochemical step potential measurements. X-ray absorption spectroscopy indicates that the absorption energy of the W L III-edge shifts towards lower energy with the insertion of Li + ions and electrons. The results of radial distribution functions reveal that the increase in the distance of the WO bonds is caused by the reduction in W ions. Li xWO 3 and Li 2WO 4 are formed at 0.5V and 1.0V, respectively, during electrochemical insertion, as observed by transmission electron microscopy. The Raman scattering analysis indicates that only two ionic states, W 4+ and W 6+, exist in the WO 3 films, due to excess injection of electrons and Li + ions. We suggest that the degradation of the electrochromic properties of the WO 3 films during electrochemical cycles is related to the formation of different W ionic states.

Original languageEnglish
Article number225303
JournalJournal of Physics D: Applied Physics
Volume45
Issue number22
DOIs
Publication statusPublished - Jun 6 2012
Externally publishedYes

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Electronic, Optical and Magnetic Materials
  • Acoustics and Ultrasonics
  • Surfaces, Coatings and Films

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