Fabrication and characterization of thin Nb2O5 blocking layers for ionic liquid-based dye-sensitized solar cells

The preparation of a novel Nb2O5 blocking layer deposited between fluorine-doped tin oxide (FTO) and nanocrystalline TiO2 layer and its application for hydrophobic dye Z-907 sensitized ionic liquid-based solar cells have been studied. The Nb2O5 blocking layer prepared by spray pyrolysis method on FTO has been characterized by scanning electron microscope (SEM) equipped with energy dispersion X-ray analysis (EDX), transmit electron microscope (TEM), electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS). Thin Nb2O5 films work as a potential blocking layer between FTO and nanocrystalline TiO2 layer in ionic liquid electrolyte cells, improving Voc and finally giving a better conversion efficiency of dye-sensitized TiO2 solar cells. Impedance spectroscopy indicates that the blocking layer can increase shunt resistance especially related with the charge transport at FTO–TiO2/dye/ionic liquid electrolyte and decrease the series resistance to some extent by constructing the potential barrier. Analysis of diffusion coefficient and lifetime of electrons in the cells confirms that they compensate each other when the blocking layer was introduced, leading to a little influence on the diffusion length (L). The remarkable improvements of Voc and fill factor for the DSCs suggest that the thin Nb2O5 is an effective blocking layer at FTO and TiO2 interface, contributing to unidirectional transport of electrons in the ionic liquid-based dye-sensitized nano-TiO2 solar cells.