Effect of TiO^sub 2^ modification on urchin-like orthorhombic Nb^sub 2^O^sub 5^ nanospheres as photoelectrodes in dye-sensitized solar cells

TiO2 modification via TiCl4 treatment has been widely used to improve the power conversion efficiency (PCE) of dye-sensitized solar cells (DSSCs), in which the effects usually attribute to the inhibition of charge recombination by barrier effect. Niobium pentoxide (Nb2O5) is considered a promising photoelectrode material for DSSCs. Here we prepared urchin-like orthorhombic Nb2O5 nanospheres consisting of ultrathin nanorods by a hydrothermal method, which were further developed as photoelectrodes for DSSCs. The TiO2 modification on the urchin-like orthorhombic Nb2O5 nanospheres increases the photocurrent and PCE of the DSSCs. However, the impedance spectroscopy showed that charge recombination was not reduced by the TiO2 modification. The improvement in the photocurrent and PCE has been attributed to the enhanced absorption of dye molecules (N719). The results indicate that the enhancement of dye absorption for orthorhombic Nb2O5 photoelectrodes is the desirable approach to improve the performance of orthorhombic Nb2O5-based DSSCs.