Nanostructured TiO2 and S-doped TiO2 thin films with high transparency were prepared on glass substrate through ultrasonic-assisted spray pyrolysis technique. The effect of sulfur doping on morphological, optical, and structural properties of TiO2 was studied by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, FTIR, photoluminescence spectroscopy, and UV–visible absorption spectroscopy techniques. Because of the high uniformity and monodispersity of the prepared TiO2 and S-doped TiO2 thin films, these samples have high visible-light transparency of about 81.89% and 69.73%, respectively. Both the TiO2 and S-doped TiO2 thin films have anatase crystal structure; however, introduction of the S dopant in the lattice of TiO2 creates some oxygen vacancies and structural defects in the S-doped TiO2 sample. Because of the presence of defects which could act as charge trapping center in the structure of S-doped TiO2, this sample has lower electron–hole recombination rate than undoped TiO2. Furthermore, sulfur doping results in the band-gap narrowing of TiO2. Compared to the undoped TiO2 sample, suppression of the electron–hole recombination and band-gap narrowing in the S-doped TiO2 thin film result in the enhancement of its visible-light photocatalytic activity.
