Influence of Fe ions in characteristics and optical properties of mesoporous titanium oxide thin films

Fe-doped mesoporous titanium dioxide (M-TiO2-Fe) thin films have been prepared on indium tin oxide (ITO) glass substrates by sol-gel and spin coating methods. All films exhibited mesoporous structure with the pore size around 5-9 nm characterized by small angle X-ray diffraction (SAXRD) and further confirmed by high resolution transmission electron microscopy (HRTEM). Raman spectra illustrated that lower Fe-doping contributed to the formation of nanocrystalline of M-TiO2-Fe thin films. X-ray photoelectron spectroscopy (XPS) data indicated that the doped Fe ions exist in forms of Fe3+, which can play a role as e− or h+ traps and reduce e−/h+ pair recombination rate. Optical properties including refractive indices/n, energy gaps/Eg and Urbach energy width/E0 of the thin films were estimated and investigated by UV/vis transmittance spectra. The presence of Fe content extended the light absorption band and decreased the values of n, implying enhanced light response and performance on dye-sensitized solar cells (DSSC). The optimum Fe content in M-TiO2-Fe thin films is determined as 10 mol%, for its compatibility of well crystalline and well potential electron transfer performance.