Polarization-oriented enhancement of ferroelectric photovoltaic performance in BiFeO₃ synapses for neuromorphic vision systems

Ferroelectric photovoltaic (PV) synapses, which utilize polarization to precisely tune the photocurrent as synaptic weight, have attracted increasing interest due to their excellent polarization controllability, fast response speed, and low energy consumption. Herein, we identify a [111] polarization-oriented strategy that significantly enhances the ferroelectric PV performance of BiFeO₃ (BFO) epitaxial-film devices without compromising their ferroelectricity. The photocurrent and power conversion efficiency of the [111]-oriented BFO device are two orders of magnitude larger than that of [001]-oriented BFO. The [111]-oriented BFO device exhibits the highest remnant polarization (∼120 μC/cm²) among those reported ferroelectric PV devices, as well as excellent fatigue resistance. The high electric-field tunability of photocurrent enables [111]-oriented BFO device to function as a ferroelectric PV synapse, showing optoelectronic long-term potentiation/depression synaptic plasticity. Simulated [111]-oriented BFO synapse arrays achieve various neuromorphic tasks such as in-sensor image recognition with a high accuracy of more than 94% and edge feature extraction by using them as an in-sensor convolution kernel. This work demonstrates the superiority of the [111]-oriented BFO synapse in neuromorphic vision systems.