Fluorine-doped tin oxide films with a high figure of merit fabricated by spray pyrolysis

Fluorine-doped tin oxide (FTO) thin films were deposited by spray pyrolysis in a pulse mode at 450 °C on glass substrates, using an alcoholic solution of SnCl4·5H2O and NH4F with different F/Sn ratios in the precursor solution. The film structure was nanocrystalline for all molar F/Sn ratios in the solution from 0 to 1.0. Postdeposition annealing treatments were not carried out. The films with a F/Sn = 0.35–1.0 ratio present a high grain orientation in the (200) crystallographic plane. A minimum sheet resistance of 4.5 Ω/sq, a resistivity of 2.2 × 10−4Ω cm, a maximum electron mobility of 21.6 cm2/V s, and a carrier concentration of 1.7 × 1021cm−3, corresponding to a strong degeneration of the electron gas in the conduction band, as well as a mean value of the transmittance of 0.84 in the visible spectral range, were obtained for the films fabricated with a F/Sn = 0.5 ratio. A high value of the figure of merit was obtained using two methods (38.8 × 10−3Ω−1and 5.75 Ω−1), that is, comparable with the highest values reported to date.