Electrochromism and small-polaron hopping in oxygen deficient and lithium intercalated amorphous tungsten oxide films
2015 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 118, no 2, 1-9 p., 024901Article in journal (Refereed) Published
Thin films of LixWO3-z with 0 <= x <= 0.27 and 0 <= z <= 0.27 were prepared by sputter deposition followed by electrochemical lithiation. Kramers-Kronig-consistent complex dielectric functions were obtained for these films by numerical inversion of experimental spectra of optical transmittance and reflectance by using a superposition of Tauc-Lorentz and Lorentz oscillator models. Low-energy optical absorption bands were induced by oxygen vacancies and/or by electrochemical intercalation of Li+ species together with charge compensating electrons. The experimental optical conductivity was fitted to a small-polaron model for disordered systems with strong electron-phonon interaction, taking into account transitions near the Fermi level. The optical absorption is due to small-polaron hopping and associated with the formation of W5+ states due to transfer of electrons from oxygen vacancies and/or insertion of Li+ species. The results also show increases in the Fermi level, caused by oxygen deficiency or Li+ insertion, which occur along with a band gap shift towards higher energies for the Li+ intercalated films.
Place, publisher, year, edition, pages
2015. Vol. 118, no 2, 1-9 p., 024901
Engineering and Technology Nano Technology
IdentifiersURN: urn:nbn:se:uu:diva-260295DOI: 10.1063/1.4926488ISI: 000357961000032OAI: oai:DiVA.org:uu-260295DiVA: diva2:847714
FunderSwedish Research CouncilEU, FP7, Seventh Framework Programme, 267234