Undoped tin oxide thin films obtained by the sol gel technique, starting from a simple precursor solution

In this work, we report the synthesis and the structural, optical and electrical properties of undoped tin oxide thin films obtained by the sol–gel technique. The films have been prepared from a simpler precursor solution than other ones reported; it is based on stannous chloride (SnCl2·2H2O), ethanol, glycerol and triethylamine. The films are deposited on glass slide substrates and sintered at temperatures in the 300–550 °C range, in an open atmosphere. A second thermal treatment in vacuum is made in order to decrease the resistivity of the films. The X-ray diffraction patterns show the tetragonal phase of SnO2 with a small preferential orientation in the (110) plane. All films show high optical transmission (~85%) and a direct band gap value around of 3.8 eV. The minimum resistivity value, 2 × 10−1 Ohm-cm, is obtained for the films sintered at 300 and 350 °C and thermal treated in vacuum at 500 °C for 1 h. The decrease of the resistivity with the thermal treatment in vacuum is associated with an increase in the oxygen vacancies concentration.