Bulk photovoltaic effect in monodomain BiFeO_3 thin films

摘要

The bulk photovoltaic effect of ferroelectric semiconductors is increasingly being studied for potential applications in solar energy harvesting thanks to their unique charge separation mechanism and the resultant anomalous photovoltage. However, the intrinsic properties regarding the temperature dependence of photovoltaic current and its correlation with the ferroelectric polarization in such systems still require proper understanding. Here, by studying monodomain BiFeO_3 thin films with only a single ferroelectric variant, we demonstrate that the photovoltaic current of BiFeO_3 ferroelectric semiconductors possesses a preferred direction depending on the light polarization direction and working temperature, which is not along the ferroelectric polarization direction. The results indicate that the bulk photovoltaic effect originates from non-centrosymmetry of ferroelectric semiconductors but is independent of the ferroelectric polarization. Moreover, we showed that the bulk photovoltaic effect can be tailored by modifying the activity of sub-band gap levels via chemical doping, thus enhancing the power conversion efficiency in ferroelectric semiconductors.