Bandgap Engineering in TiO2 By Sulfurization

Tuesday, October 13, 2015: 09:40
Ellis West (Hyatt Regency)
W. J. Shin (Arizona State University), A. H. Granados (CIICAp-UAEMor and IER-UNAM), H. Hu (Instituto de Energías Renovables (IER), UNAM), and M. Tao (Arizona State University)
Previous studies have proposed bandgap narrowing by anion (e.g. N, C, or S) or cation doping into the lattice of TiO2. Sulfur is of particular interest, as TiS2 has a close-to-zero bandgap. By mixing TiO2 and TiS2 into oxysulfide, a new semiconductor with a suitable bandgap for photovoltaics or solar water splitting may emerge. In this work, we investigate sulfurization of TiO2 thin films through H2S gas-phase diffusion. The TiO2 films were prepared by the sol-gel method. Transmittance and X-ray diffraction analyses indicate that the TiO2 films have an anatase phase with a direct bandgap of 3.2 eV. The films are sulfurized in H2S under different pressure, temperature and time. It is found that sulfurization results in a second, narrower bandgap phase in TiO2. At 600˚C, the anatase TiO2 almost completely disappears. The results suggest that sulfurization by H2S is effective in narrowing the bandgap of TiO2.