Dye-sensitized solar cells (DSSCs) based on titanium dioxide (TiO2) have been extensively studied because of their promising low-cost alternatives to conventional semiconductor based solar cells. DSSCs consist of molecular dye at the interface between a liquid electrolyte and a mesoporous wide-bandgap semiconductor oxide. Most efforts for high conversion efficiencies have focused on dye and liquid electrolytes. However, interface engineering between dye and electrode is also important to reduce recombination and improve efficiency. In this work, for interface engineering, we deposited semiconducting ferroelectric BiFeO3 with bandgap of 2.8 eV on TiO2 nanoparticles and nanotubes. Photovoltaic properties of DSSCs were characterized as a function of thickness of BiFeO3. We showed that ferroelectric BiFeO3-coated TiO2 electrodes enable to increase overall efficiency of DSSCs, which was associated with efficient electron transport due to internal electric field originating from electric polarization. It was suggested that engineering the dye-TiO2 interface using ferroelectric materials as inorganic modifiers can be key parameter for enhanced photovoltaic performance of the cell.

Recently, many lead-free piezoelectric materials have been investigated for the replacement of existing Pb-based piezoelectric ceramics because of globally increasing environmental interest. There has been remarkable improvement in piezoelectric properties of some lead-free ceramics such as (Bi, Na) Ti03-(Bi, K) Ti03-BaTiO3, (Na, K) Nb03-LiSbO3, and so on. However, no one still has comparable piezoelectric properties to lead-based materials. Therefore, new lead-free piezoelectric ceramics are required. BiFeO3 has a rhombohedrally distorted perovskite structure at room temperature and a very high Curie temperature (Tc=1,100 K). And a very large electric polarization of 50~60 uC/cm2 has been reported both in epitaxial thin film and single crystal BiFeO3. Therefore, a high piezoelectric effect is expected also in a BiFeO3 ceramics. The recent research activities on BiFeO3 or BiFeO3-based solid solutions are reviewed in this article.