Effect of fluorine content on the morphological, structural, optical and electrical properties of nanostructured SnO2 films

This paper reports morphological and structural details, optical and electrical properties of fluorine doped SnO2 thin films prepared via spray pyrolysis route using SnCl2 center dot 2H(2)O as precursor and methanol as a solvent. The effect of fluorine concentration on the properties of the films is presented and discussed. X-ray diffraction pattern reveals the presence of SnO2 films in the rutile structure with a preferential growth along the ( 200) direction. FTIR spectrum confirms the films to be made of SnO2. EDS was used to estimate the fluorine concentration. SEM reveals the surface of FTO to be made of nanocrystalline particles. The grain size calculated using Debye-Scherrer formula is in the range of 8-34 nm. Film thickness measured using optical transmission method is in the range of 425-538 nm. The sheet resistance was found to decrease with increase in fluorine concentration, to a minimum of 6.35 Omega/rectangle for 7.5 mol% of NH4F, and it showed an increase beyond this concentration. The 2.5mol% of F doped films gave 95.20% transmission at 704 nm. The calculated reflectivity in the IR region is 93.57% for 7.5mol% of F doping, and figure of merit for the same film is 0.025(Omega/rectangle)(-1) at 550 nm. The total work was optimized by fixing the temperature at 550 degrees C for the usage of Electrochromic Device preparations on FTO coated glass substrates.