Optimization of substrate temperature and characterization of tin oxide based transparent conducting thin films for application in dye-sensitized solar cells

Tin oxide (SnO2) thin films were prepared by nebulizer spray pyrolysis (n-SP) of SnCl2.2H2O precursor on glass substrates preheated at substrate temperatures varying from 200 °C to 500 °C. The structural, surface, and optical studies of the films were carried out to validate the results of the electrical analysis which support the utilization of the prepared films for the transparent conducting applications in dye-sensitized solar cells (DSSCs). The X-ray diffraction patterns revealed that the films are polycrystalline in nature with high crystalline quality, relatively at a lower substrate temperature of 350 °C. Film thickness was found to be around 350 nm, and the crystallite size was in the range of 50 nm with low lattice strain and dislocation density. The surface morphological analysis shows the uniform surfaces with homogeneous, closely-packed grains. Optical studies indicate that the films are highly uniform, and good optical quality with 80% transparency was observed at 560 nm for the films deposited at 350 °C. The electrical measurements revealed that the films were n-type with the electrical resistivity in the range of 7.83 × 10− 2 Ω-cm. Subsequently, fluorine doping reduced the film resistivity further to 2.9 × 10− 3 Ω-cm. The dye-sensitized solar cell device structure (Glass/FTO/TiO2 film/N-719 dye/electrolyte/platinized FTO/Glass, having a surface area of 1 cm2) developed using the optimized fluorine doped tin oxide thin films, generates the conversion efficiency of 4.02% under AM 1.5 illumination of simulated solar light.