Highly-efficient electrochromic performance of nanostructured TiO2 films made by doctor blade technique

Electrochromic TiO2 anatase thin films on F-doped tin oxide (FTO) substrates were prepared by doctor blade method using a colloidal solution of titanium oxide with particles of 15 nm in size. The films were transparent in the visible range and well colored in a solution of 1 M LiClO4 in propylene carbonate. The transmittances of the colored films were found to be strongly dependent on the Li+ inserted charges. The response time of the electrochromic device coloration was found to be as small as 2 s for a 1 cm2 sample and the coloration efficiency at a wavelength of 550 nm reached a value as high as 33.7 cm2 C−1 for a 600 nm thick nanocrystalline-TiO2 on a FTO-coated glass substrate. Combining the experimental data obtained from in situ transmittance spectra and in situ X-ray diffraction analysis with the data from chronoamperometric measurements, it was clearly demonstrated that Li+ insertion (extraction) into (out of) the TiO2 anatase films resulted in the formation (disappearance) of the Li0.5TiO2 compound. Potential application of nanocrystalline porous TiO2 films in large-area electrochromic windows may be considered.