Epitaxial Stress-Stabilized Rhombohedral Ferroelectric and Dual-Phase Structure Induced Large Photovoltaic Effect in YFeO₃ Films

Ferroelectric photovoltaic materials have been extensively investigated owing to their ability to generate an above-bandgap photovoltage. YFeO₃ exhibits potential as a photovoltaic material owing to its suitable bandgap, excellent stability, and environmental compatibility; however, its inherently weak ferroelectric properties limit its practical application. This study reports and systematically investigates a ferroelectric rhombohedral phase in YFeO₃ films. The R3c phase was found to stabilize by epitaxial stress, wherein changes in the bond length led to atomic displacements that induce ferroelectricity. The Pnma phase gradually forms and becomes embedded within the R3c phase matrix owing to stress relaxation and growth defects such as dislocations with increasing film thickness, eventually forming a dual-phase structure. A chemical potential imbalance, formed at the ferroelectric/paraelectric phase boundary postpolarization, results in a large photogenerated voltage of up to 8.82 V under white light illumination with an energy density of 100 mW/cm². These findings elucidate the role of the stress-stabilized rhombohedral phase and dual-phase structure in enhancing ferroelectric photovoltaic effects. These results contribute to the exploration of multiferroic materials and the understanding of structure-property relationships. Furthermore, they offer crucial insights for developing high-performance photovoltaic devices.