Statistics: A spectator sport

The photovoltaic effects in Bi0.9La0.1FeO3 thin films are found to be strongly dependent on the oxygen concentration which can be manipulated by cooling oxygen pressure. Switchable photovoltaic effects can be observed without any electric field applied in low oxygen pressure cooled samples, however, it is hard to detect with high oxygen pressure cooled samples, until the occurrence of polarization flipping by applied electric field. This switchable photovoltaic effects can be explained well by the variation of the Schottky barrier at the metal–Bi0.9La0.1FeO3 interface resulting from the combination of oxygen vacancies and polarization. The sign of photocurrent could be independent of the direction of polarization when the modulation of the energy band induced by oxygen vacancies is large enough to offset that induced by polarization. The photo-current induced by the electro migration of oxygen vacancies is variable due to the diffusion of defects such as oxygen vacancies or the recombination of oxygen vacancies with hopping electrons. Our work provides new ideas for tuning the photovoltaic effect in ferroelectric materials.