Extraordinary piezoresponse in free-standing two-dimensional Bi₂O₂Se semiconductor toward high-performance light perception synapse

Localized strain engineering has a higher spatial modulation precision because it can generate noteworthy out-of-plane deformation, which shows novel physical properties for developing functional devices. However, the relevant research and the coupling with external fields has not been well developed. Here, we focus on disclosing the strain-optical-electrical cooperative interactions of the emerging two-dimensional (2D) Bi₂O₂Se semiconductor with a free-standing structure. The suspended Bi₂O₂Se exhibits remarkable out-of-plane electromechanical coupling. The piezoelectric coefficient of ∼ 13.1 pm/V from 8 nm nanoflake significantly surpasses that from its flat structure and the majority 2D materials. The generated back-to-back built-in electric field efficiently regulates transport carriers under optical stimulation, leading to a larger photogenerated current enhancement about 10⁴ of a suspended Bi₂O₂Se device without gate voltage modulation. This device also displays an ultra-high-performance artificial synaptic function, which has thousands of changes in synaptic weight, superior paired-pulse facilitation, bio-similarity relaxation times, and an interesting “learning-experience” behavior similar to human beings. The realization of an electromechanical visualization model and excellent optoelectronic synaptic functions can promote the further development of 2D materials based flexoelectric applications.