Visible-light-response iodine-doped titanium dioxide nanocrystals for dye-sensitized solar cells

We report on the synthesis of visible-light-response iodine-doped TiO2 nanocrystals (I-TNCs), and their implementation as photoanodes of dye-sensitized solar cells (DSSCs). The preparation of I-TNCs starts with hydrolysis of titanium isopropoxide in iodine-based aqueous system, followed by hydrothermal treatment and annealing process to achieve anatase structure. The I-TNCs were characterized by TEM, SEM, XRD, EDS and XPS. Under an optimized I/Ti doping ratio of 20 mol%, the photovoltaic performance of the cell based on I-TNCs is significantly better, with an energy-conversion efficiency of 7.0% under 100 mW cm(-2) illumination, which is 42.9% higher than that of the cell based on undoped TNCs. Interestingly, the I-TNCs-based cell shows a higher conversion efficiency of 10.0% under 30 mW cm(-2) illumination. The improved performance is explained by the expanded visible-light harvesting (characterized by incident photon to current conversion efficiency and UV-vis absorption spectra), lowered recombination resistance (characterized by electrochemical impedance spectroscopy, Rrec) together with prolonged electron lifetime tau(e). These results suggest substantial potential of TiO2 nanocrystals with controlled doping in DSSC application.