Investigations on crystallinity and surface oxidation states of Nb:TiO2 DC-sputtered films

Abstract

Pure anatase-ordered Nb:TiO2 thin films were prepared using a pulsed-DC sputtering source with a composite (TiO2)0.94Nb0.06 cathode. A mixture of Ar and O2 was used as discharge environment, under the total pressures of 1.0 × 10−2 and 5.0 × 10−2 mbar. The related effects of these parameters on film properties, associated with different deposition rates were monitored. The DC discharge was supplied by a pulsed voltage supply with a repetition rate of max. 350 kHz working in constant power mode, for two values of the injected power into discharge, 100 W and 200 W. Polycrystalline Nb-doped TiO2 thin films with the thickness in the range of 300 and 1100 nm and Nb content ranging between 2.1 and 2.8 at.% were deposited on heated (100)Si and glass substrates. Their optical transmittance measurements were used to derive the optical band gap using the Tauc plots spectra. Data processing showed band gap energy, Eg, values ranging between 3.21 and 3.31 eV. Upon increasing the dopant content, a decrease in surface roughness and film crystallinity were observed. The results were used to design conductive electrodes in dye-sensitized solar cells with improved performances.