Switchable ferroelectric photovoltaic in the low bandgap cobalt-substituted BiFeO3 epitaxial thin films

The proposal of the ferroelectric photovoltaic effect provides a spick-and-span concept for breaking through the bottleneck of traditional heterojunction energy conversion and the photoelectric memory device. However, the wide bandgap, low carrier transport capacity, and small photocurrent of ferroelectric materials limit its ferroelectric photovoltaic applications. Here, chemical regulation of cobalt substitution has been used to effectively reduce bandgap and improve ferroelectric photovoltaic properties. High-quality Co-substituted BiFeO3 epitaxial films were fabricated by magnetron sputtering. The enhanced tetragonality can be obtained by introducing the chemical strain of cobalt. The ferroelectric properties of present films have been significantly improved with a fivefold increase in remnant polarization, resulting from the enhanced lattice distortion of the oxygen octahedron. The enhanced hybridization of electron orbitals and the atomic structure has been revealed by synchrotron radiation and the high-resolution HAADF-STEM. Intriguingly, the optical bandgap has been reduced from 1.97 eV to1.47 eV, which is close to the ideal bandgap. The switchable ferroelectric photovoltaic can be realized by changing the direction of polarization, and the open-circuit voltage and short-circuit current have increased to 1.7 and 1.8 times, respectively. This work further reveals the application potential of chemical-strain-modulated epitaxial films in the field of optoelectronics and information storage.