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The electrical transport properties of fluorine-doped tin oxide thin films prepared by a sol-gel dip-coating technique have been studied in detail. X-ray diffraction patterns confirm the crystalline nature of the films having a grain size in the nanometer range. The fluorine concentration in the films was varied from 1.62 to 12% and was measured by energy dispersive X-ray analysis. It was observed that the current-voltage (I -V) characteristics of the films were non-linear in nature, which could be explained by the Poole-Frenkel model of thermionic emission. With an increase in temperature, the non-linearity becomes more and more pronounced. The presence of adsorbed oxygen and fluorine atoms at grain boundaries is assumed to be the cause of this effect. These atoms produce defect levels, which trap electrons and create a potential barrier across the grain boundaries. In the presence of an external field, the barrier height is attenuated, resulting in the thermionic emission of electrons from the trapped level to the conduction band. The trapped potentials (φ t ) are calculated for different doping concentrations in the films. These values range from 589 to 703 meV. The maximum room temperature conductivity of the films was found to be of the order of 1 Ω -1 cm -1 . Activation energies (E a ), calculated from Arrhenius plots, range from 85 to 130 meV for different fluorine concentrations in the films. may be of use in the production of films with improved electrical characteristics. Previously, Scalvi et al.[12] reported the Poole-Frenkel effect in antimony-doped tin oxide (ATO) thin films derived from the SGDC route. However, to our knowledge, no communication on this subject for FTO films has been reported so far. ExperimentalSnCl 2 ⋅ 2H 2 O (99.95%), HF (40%) and isopropyl alcohol (99.8%) were taken as starting materials. Details of the deposition conditions are described elsewhere [9]. Several solutions were made by varying the amount of HF taken in the starting solutions, which resulted in the fluorine concentration in the films ranging from 1.62 to 12%. The resulting solutions were mixed with isopropyl alcohol, stirred for 1 h at a temperature of ~70-75 °C and then aged for 2 h to get the required sol. Ultrasonically cleaned glass substrates were dipped into and then withdrawn vertically from the solution very slowly at a rate of 8 cm/min for 10 to 15 times and then dried at ~80 -100 °C to form the gel. Thus the films were deposited layer by layer to achieve uniformity. Thereafter the films were annealed at ~300-325 °C in air for half an hour to oxidize all unreacted Sn bonds to form the required FTO films.The structural properties of the films were studied by X-ray diffraction (XRD; Philips PW 1730/PW 1710, using CuK α line). Fluorine concentrations in the films were measured by energy dispersive X-ray analysis (EDX; Leica S-440, Oxford ISIS), which could detect elements from boron (5) to uranium (92). Electrical characteristics of the films were studied by the standard four-probe method using a Keithley mu...

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