Properties of fluorine-doped SnO2 thin films by a green sol–gel method

Abstract Fluorine doped tin oxide (FTO) films were fabricated on a glass substrate by a green sol–gel dip-coating process. Non-toxic SnF 2 was used as fluorine source to replace toxic HF or NH 4 F. Effect of SnF 2 content, 0–10 mol%, on structure, electrical resistivity, and optical transmittance of the films were investigated using X-ray diffraction, Hall effect measurements, and UV–vis spectra. Structural analysis revealed that the films are polycrystalline with a tetragonal crystal structure. Grain size varies from 43 to 21 nm with increasing fluorine concentration, which in fact critically impacts resultant electrical and optical properties. The 500 °C-annealed FTO film containing 6 mol% SnF 2 shows the lowest electrical resistivity 7.0×10 −4  Ω cm, carrier concentration 1.1×10 21  cm −3 , Hall mobility 8.1 cm 2 V −1  s −1 , optical transmittance 90.1% and optical band-gap 3.91 eV. The 6 mol% SnF 2 added film has the highest figure of merit 2.43×10 −2  Ω −1 which is four times higher than that of un-doped FTO films. Because of the promising electrical and optical properties, F-doped thin films prepared by this green process are well-suited for use in all aspects of transparent conducting oxide.