Enhanced Charge Transport Properties of Dye-Sensitized Solar Cells Using TiNxOy Nanostructure Composite Photoanode

In this Article, the improvement in the conversion efficiencies of dye-sensitized solar cells (DSSCs) was observed by integrating a small amount of thermally oxidized titanium nitride (TiNxOy) particles into the hydrothermally growth TiO2 nano- particles to form the composite photoanode. The oxidation of titanium nitride (TiN) to TiNxOy (N-doped TiO2) was achieved using a simple single-step annealing process at 450 °C for 1 h. The existence of the OTiN linkage in TiNxOy was verified using X- ray photoemission spectroscopy (XPS). The DSSCs using the composite photoanode with 5 wt % of TiNxOy particles in TiO2 showed optimum conversion efficiency with a 25.6% improvement over the conventional DSSCs using only the mesoporous TiO2 layer as photoanode. Higher incident photon-current conversion efficiency (IPCE) values were also obtained for these composite photoanodes. This marked improvement was attributed to the combined synergetic effects of an extra absorption in the visible region and an enhanced efficiency in the electron transport. The extra absorption region at 400�500 nm for TiNxOy was observed using a UVvis spectrophotometer. In addition, the reduction of charge transport resistance in the composite photoanode as verified using electrochemical impedance spectroscopy (EIS) has also contributed to faster electron transport through the interpenetrating oxide layer.