Thickness Dependence of Photovoltaic Effect in BiFeO3 Thin Films Based on Asymmetric Structures

BiFeO3 (BFO) thin films with different layers were deposited on Pt/Ti/SiO2/Si substrates via the sol-gel method, and the effect of nonuniform electric field formed by asymmetry electrodes on the photovoltaic properties has been investigated through experimental approaches. The Au/BFO/Pt heterostructures show 1.3 V open-circuit voltages and similar to 0.242% photovoltaic power conversion efficiency when illuminated under sunlight (AM 1.5), this high efficiency is at least one order of magnitude larger than many other values thus far reported for BFO-based devices prepared by the spin coated method. The film layer dependence of the photovoltaic effect suggests that the large open-circuit voltage and high efficiency are contributed by both the ferroelectric polarization and the asymmetric structures formed by top and bottom electrodes. Theoretical analysis indicates that the efficiency may be further significantly improved by increasing the number of film layers and the nonuniform depolarization field, implying potential applications.