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

Abstract

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 τ_e. These results suggest substantial potential of TiO₂ nanocrystals with controlled doping in DSSC application.