Large photovoltaic response in rare-earth doped BiFeO3 polycrystalline thin films near morphotropic phase boundary composition

Abstract

The photovoltaic (PV) properties of polycrystalline Bi1−xLaxFeO3 (x = 0–0.3) films have been explored. The X-ray diffraction study reveals that there is a gradual phase transition with the increase in La doping. The composition x = 0.25 is found to be the morphotropic phase boundary (MPB), beyond which the system turns into the non-/antipolar orthorhombic phase. The polarization measurements reveal improved ferroelectric properties with the maximum remanent polarization observed for the x = 0.25 film. A systematic study on the direct and indirect bandgaps of the films has shown a decreasing trend with composition. Interestingly, the PV studies exhibit a maximum open-circuit voltage of 1.30 V for the x = 0.25 film which is three times larger than the value observed for pure BiFeO3 (BFO) (0.47 V). The enhanced PV response in La-doped BFO correlates with the polarization and the change in direct/indirect bandgaps associated with structural instability near the MPB composition. The approach used in this work for enhancing the PV performance in ferroelectric BFO through the combined effects of polarization, bandgaps and competing structures provides a better pathway for improving the ferroelectric PV effect.