Aerosol-assisted chemical vapour deposition synthesis of fluorine-doped tin oxide (FTO) for dye-sensitized dollar cells (DSSCs): Effect of doping with fluorine

In this study, investigation of influence of fluorine doping on conductivity of transparent conducting tin oxide (SnO₂) for dye-sensitized solar cells (DSSCs) was carried out. Tin Oxide (SnO₂) doped with different percentage of fluorine was deposited by the Aerosol Assisted Chemical Vapour Deposition on the substrate layers of transparent glass slide. Effect of wavelength on the optical properties, and also characterization of the substrate layers was investigated. The results obtained from the UV-VIS spectra indicated that fluorine was successfully doped on the substrate. The doped SnO₂ was found to have a lower absorbance when compared to the un-doped one. Transmittance obtained shows that as the wavelength increased, better transmittance was obtained; for instance above 80% for 12% doped F:SnO₂, but at lower wavelength of 230 nm. The highest optimum transmittance of 50% was obtained for 4% doped F:SnO₂. The thickness of SnO₂ nanoparticles was 150 nm for the un-doped; 200 nm for the 4% doped SnO₂; 50 nm for the 8% doped SnO₂; and 40 nm for the 12% doped SnO₂. The conductivity and mobility were 2.426 (Ωcm)^-1 and 1.347 cm²/vs for un-doped; 5.039 (Ωcm)^-1 and 11.40 cm²/vs for 4% doped SnO₂; 20.85 (Ωcm)^-1 and 7.457 cm²/vs for 8% doped SnO₂; and 1.596 (Ωcm)^-1 and 7.457 cm²/vs for 12% doped SnO₂. Conclusively, it is evident that FTO is greatly affected by the wavelength as well as the percentage of doping. In case of thin films, conductivity will also depend upon the film thickness. If the thickness is too large beyond an optimum limit, conductivity decreases because grain size of nanoparticle will increase leading to an increase in bandgap (quantum confinement effect).