Appreciable photovoltaic responses to visible light are observed in epitaxial ferroelectric BiFeO3 thin films by sputtering deposition. The photocurrent direction is opposite to the BiFeO3 polarization vector and can be switched by poling the films in different directions (see figure). The as‐deposited films are strongly self‐polarized, exhibiting significant photovoltaic response before any electrical poling process.

Photovoltaic effect in ferroelectric thin films with thickness below 100nm was investigated through both theoretical and experimental approaches. Unprecedented high photovoltaic power conversion efficiency around ∼0.28% was achieved with epitaxial (Pb0.97La0.03)(Zr0.52Ti0.48)O3 ferroelectric thin films, which is about 2 orders of magnitude higher than the reported in literature for ferroelectrics. Theoretical analysis indicated that efficiency can be further significantly improved by reducing the thickness in nanoscale. Extremely high efficient bulk photovoltaic effect is predicted in high quality ferroelectric ultrathin films.

Considering energy band alignment and polarization effect, ferroelectric BiFeO3 thin films are proposed as the photoanode in a monolithic cell to achieve unassisted photocatalytic water splitting. Significant anodic photocurrent was observed in our epitaxial ferroelectric BiFeO3 films prepared from sputter deposition. Both negative polarization charges and thinner films were found to promote the anodic photocatalytic reaction. Ultraviolet photoelectron spectroscopy proved that the conduction and valence band edges of BiFeO3 straddle the water redox levels. Theoretical analyses show that the large switchable polarization can modify the surface properties to promote the hydrogen and oxygen evolutions on the surfaces with positive and negative polarization charges, respectively.

It was discovered that the dielectric constant of the electrodes substantially determines the photovoltaic output in (Pb0.97La0.03)(Zr0.52Ti0.48)O3 ferroelectric thin films. With the screening charges distributed extensively away from the electrode interfaces, the use of the electrodes with a high dielectric constant gives rise to dramatically enhanced magnitude of photocurrent in photovoltaic thin films, and extremely high photovoltaic efficiency is theoretically predicted to be possible in ferroelectric ultrathin films or nanostructures.