Fluorine highly doped nanocrystalline SnO2 thin films prepared by SPD technique

• SnO2 pure and fluorine highly doped thin films deposited by the SPD at 450 °C on glass substrate.
• The XRD studies of the prepared films showed polycrystalline nature and tetragonal phase.
• Optical studies showed that the films have high transmittance. Absorption edges of SnO2:F films blue shifted.
• Band gap of SnO2 thin films increased with increased fluorine mole ratio. This is related to B–M effect.
• EDX spectra well defined peaks corresponding to Sn, O and F and the final film stoichiometry is SnO2:F.

Pure and fluorine highly doped SnO2 (TO and FTO) thin films with different dopant concentrations (0.15, 0.25, 0.35 mol/l) have been prepared by spray pyrolysis technique at substrate temperature 450 °C. The crystal structure and surface morphology of the prepared films were characterized by using X-ray diffraction and scanning electron microscopy SEM. The XRD patterns show polycrystalline structure in nature with tetragonal (rutile) phase. The average crystallite size decreases with increasing of dopant concentrations and its values in the range (32–56) nm which indicate that all films have nanocrystalline structure. The SEM images show a homogeneous and smooth uniform surface with no detectable micro-cracks, the EDX spectra confirm the stoichiometry of the prepared films. The optical properties of the films were investigated by UV–vis spectrophotometer. In the visible range, the optical transmittance (T%) of the films with varying dopant concentrations was found to be (83–98)% and the fundamental absorption edge shifted toward higher energies (blue shift) with increasing of fluorine dopant concentration. The energy band gap value of pure SnO2 was 3.95 eV and it increases to 4.04, 4.08 and 4.1 eV with the increasing of dopant concentration, this behaviors can be attribute to the (B.M) effect or Burstein–Moss shift.