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 <i>R</i>3<i>c</i> phase was found to stabilize by epitaxial stress, wherein changes in the bond length led to atomic displacements that induce ferroelectricity. The <i>Pnma</i> phase gradually forms and becomes embedded within the <i>R</i>3<i>c</i> 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.