Nanoscale excitonic photovoltaic mechanism in ferroelectric BiFeO3 thin films

Abstract

We report an electrode-free photovoltaic experiment in epitaxial BiFeO3 thin films where the picosecond optical absorption arising from carrier dynamics and piezoelectric lattice distortion due to the photovoltaic field are correlated at nanoscale. The data strongly suggest that the photovoltaic effect in phase-pure BiFeO3 originates from diffusion of charge-neutral excitons and their subsequent dissociation localized at sample interfaces. This is in stark contrast to the belief that carrier separation is uniform within the sample due to the lack of center of symmetry in BiFeO3. This finding is important for formulating strategies in designing practical photovoltaic ferroelectric devices.