Optical Properties of Multilayers TiO 2 /SnO 2 :F Thin films
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Optical Properties of Multilayers TiO2/SnO2:F Thin films Eleicer Ching-Prado*, Amanda Watson, Héctor Miranda and Ildeman Abrego Natural Science Department, Faculty of Science and Technology Technological University of Panama, Panama
Abstract Thin films of TiO2/SnO2:F multilayers were prepared by spray pyrolysis technique on glass substrate. The samples were prepared using titanium (IV) isopropoxide 98%, ammonium fluoride and tin(II) chloride dehydrate extra pure as precursor materials. Thus, a TiO2 thickness dependence optical study of TiO2/SnO2:F/glass system is presented. The optical property was characterized by UV-Visible transmittance spectroscopy. For all the samples, the average transmissions in the visible wavelength region (400-800 nm) were between 69 and 84%. The optical parameters, such as the real part dielectric function ε1 and the imaginary part dielectric function ε2, of TiO2 and SnO2:F in the TiO2/SnO2:F thin films structure, determined by fitting the measured optical transmittance spectra, are presented and analyzed. Among the various classical dispersion relations for the dielectric function, the Drude model combined with the Lorentzian oscillators was used to get a good fit of transmittance in the measured spectral range. Results on related parameters such as high frequency dielectric constant, plasma frequency, film thickness and band gap are presented. Introduction Titanium dioxide (TiO2), a wide band gap semiconductor material (3.2 eV for anatase and 3.06 eV for rutile), has gained considerable attention because of its applications as a photocatalyst, gas sensors and solar cell electrodes. In order to improve the process of photon absorption in dye-sensitized solar cells (DSSCs) application, nanocrystalline porousTiO2 has been extensively studied as an effective electrode material; because on the TiO2 surface a high density of dye molecules are embedded. It semiconductor is generally deposited on a transparent conducting oxide (TCO)/glass substrate, such as Sn-doped In2O3 (ITO), F-doped SnO2 (FTO), ZnO, CdO and many others [1,2]. In addition to the porous TiO2 structure in DSSCs, a compact TiO2 layer, which is utilized as a blocking layer, improves the adhesion of the TiO2 porous to the TCO/glass substrate, gives a larger TiO2/TCO contact area and decreases back electron transfer at the TCO/electrolyte interface [1]. The structure and optical properties of TiO2 depend to a large extend on the deposition method. Thus, many techniques have been used to prepare compact TiO2 thin films such as evaporation, ion beam, chemical vapor deposition, reactive D.C. magnetron sputtering and spray pyrolysis. The latter technique is very attractive because it is versatile and costeffective [3]. In this paper, thin films of FTO were deposited on glass substrate by spray pyrolysis technique and a dense TiO2 compact layer with different thickness were deposited onto the FTO/glass substrates using the same deposition method. Thus, the effect of the compact TiO2 3133 Downloaded from https:/www.cambridge.org/core.
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