engleski

Characterization of TiO2 films as nanostructured electrodes

Films containing nanosized grains of titanium dioxide (TiO2) are widely used in research into mainly optical, photochromic, electrochromic and photovoltaic devices. Our interest is to use nanostructured and porous film of TiO2 on glass substrate as electrode in dye-sensitized solar cell. For this purpose there is a desirable average grain and pore sizes [1], but also a desirable mixture of anatase and rutile crystal phases of TiO2. The structural characteristics of TiO2 films depend on the method of preparation but also on the subsequent processing of the material. Titanium dioxide films prepared via organic sol-gel route were characterised using impedance spectroscopy and GISAXS. Previous investigations by transmission electron microscopy [2] on sol-gel derived powder samples of TiO2 showed that they are polydispersed and porous, with nanometer sized grains of spherical shape. The analysis of films by GISAXS is based on the fact that the films are porous. A grain is defined as a volume of homogenous electron density. As the films are polydispersed, method gives weighted, average sizes. We followed how this parameter change with the thickness of film [3]. Electrical properties of nanstructured TiO2 films on glass substrates, prepared by sol-gel method were examined by impedance spectroscopy (IS). The insight in their morphology, that is grain sizes, pore sizes and layer thickness, was given by analysis of grazing-incidence small-angle X-ray scattering (GISAXS) data obtained by experiment at ELETTRA light source in Trieste, Italy. The used impedance spectroscopy and GISAXS are not destructive, i.e. it is not necessary to remove the films of the substrates, so samples remain in the form in which they are often used in functional applications of this material. The present study showed that IS combined with GISAXS can give functional dependence of resistivity versus grain sizes in nanostructured TiO2 films. We found that resistivity increases with the thickness of the film, which increase is related to the increase in grains size as found with GISAXS. References [1] A. Hagfeldt, M. Grätzel, Chem.Rev. 95/1 (1995) 40 [2] A. M. Tonejc, M. Gotić, B. Gržeta, S. Musić, S.Popović, R. Trojko, A. Turković and I. Mušević, Materials Science & Engineering B 40 (1996) 177. [3] M. Lučić-Lavčević, P. Dubček, O. Milat, B. Etlinger, A. Turković, D. Šokčević and H. Amenitsch, Materials Letters 36 (1998) 56.

GISAXS; Impedance spectroscopy; TiO2

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