About the structural, optical and electrical properties of SnO2 films produced by spray pyrolysis from solutions with low and high contents of fluorine

The morphological, structural, optical and electrical properties of tin-oxide-based coatings, obtained by spray pyrolysis using an alcoholic solution of SnCl4, were studied. The fluorine concentration and profile in the deposited material were determined. Samples were produced at a substrate temperature of 300 degrees C and a deposition time of 15 min. Undoped films showed a non-transparent milky appearance, an electrical resistivity of 33x10(-4) Omega cm and an optical transmittance of 70%-75% in the visible range. X-Ray and electron diffraction pattern results showed the presence of SnO2 in the cassiterite structure with a preferential growth in the (200) direction. Scanning electron micrographs showed that the surface coatings were covered by crystalline particles (size, 25 nm). Thin films obtained from NH4F solutions at fluorine concentrations in the range 1-40 wt.% showed a systematic decrease in the surface particle density and an increase in the transmittance with increasing fluorine concentration, attaining values around 85%. The resistivity decreased to 6x10(-4) Omega cm for doping in the 1-8 wt.% range, but for doping values above 8 wt.%, the resistivity increased more than fivefold.