Gradient Engineered BiFeO ₃ Ferroelectric Films for High Performance Self-Powered Photodetection

Bismuth ferrite (BiFeO 3, BFO) has attracted extensive interest for self-powered photodetection owing to its intrinsic ferroelectric photovoltaic effect and robust room-temperature polarization. However, intrinsic limitations in pure BFO films, including weak built-in electric fields and strong photocarrier recombination induced by oxygen vacancies and other defects, result in generally low photovoltaic output. In this study, multiscale synergistic control over BFO lattice distortion, defect distribution, and band structure was achieved through Sm, Ni co-doping and a gradient-stacked structure, significantly enhancing device photoelectric performance. The optimal stacked layer device delivers a markedly enhanced photocurrent density of 55.04 μA/cm 2 at zero bias, along with a responsivity of 0.0011 A/W, and the specific detectivity of 0.21 × 10 7 Jones, representing nearly a fivefold improvement over non-stacked device. Structural and photoelectric analyses reveal that the gradient-stacked configuration introduces both an oxygen vacancy gradient field and a strain gradient induced flexoelectric field. These fields cooperate with the interfacial Schottky built-in field to form a synergistic internal-field network, which effectively promotes photogenerated carrier separation and transport while suppressing recombination losses. As a result, the self-powered photoresponse of the device is substantially improved. This work demonstrates an effective internal-field engineering strategy for enhancing the photovoltaic performance of ferroelectric photodetectors and provides insights into the design of high-performance self-powered optoelectronic devices.