Enhanced optical properties and the origin of carrier transport in BiFeO3/TiO2 heterostructures with 109° domain walls

The absorption coefficient in the BiFeO3/TiO2 bilayer film prepared by simple sol-gel method has been significantly improved relative to BiFeO3 and TiO2 film. Terahertz-radiation emission presents a direct evidence for the photon-induced carrier transport in the heterostructures. First-principles calculations agree well with the experiments and present an unambiguous explanation for the charge carrier transport and the enhanced absorbance. It is induced by the large electrostatic potential drop in the interface with the 109° domain walls and the reduced recombination of electron-hole pairs in the BiFeO3 side of the heterostructure. This work provides a new route toward designing novel photovoltaic heterostructures with high efficiency.