Improved Photovoltaic Effect of Structured BiFeO₃ Film Deposited by Radio-Frequency Magnetron Sputtering.

Pure phase polycrystalline BiFeO₃ film was deposited onto FTO substrate by RF magnetron sputtering method. SEM result shows that BiFeO₃ film has the obvious porosity and large clusters which lead to the poor ferroelectric and photovoltaic properties in FTO/BiFeO₃/Ag device. However, these properties are improved in structured FTO/TiO₂/BiFeO₃/HTM/Ag device by incorporating the electron and hole transport materials. The hysteresis loop measurement demonstrates the excellent ferroelectric property with large remnant polarization (2 = 180 C/cm²) and low leakage current. The curve shows the short-circuit current density is dozens of times larger than that of FTO/BiFeO₃/Ag device. Moreover, the photovoltaic output depends on the poling field where the positive poling improves the short-circuit current density to -85 A/cm₂ and the negative poling reduces both the photocurrent and photovoltage. It is believed that the ferroelectric polarization plays a dominant role in the photovoltaic effect.