Nonvolatile Optoelectronic Synapses and Brain-Inspired Neuromorphic Applications Based on NbOCl ₂ /α-In ₂ Se ₃ Heterojunction

Two-dimensional van der Waals heterostructures have emerged as promising candidates for next-generation optoelectronic devices owing to their tunable band structures and strong light-matter interactions. However, achieving high-performance photodetection and neuromorphic functionalities within a single platform remains a major challenge, particularly in controlling distinct charge transport pathways of the same material system. Here, we report a multifunctional NbOCl₂/α-In₂Se₃ heterojunction device that integrates three conductive pathways: a NbOCl₂ channel, a hybrid vertical transport channel combining NbOCl₂ and α-In₂Se₃, and an α-In₂Se₃ surface channel. This unique trichannel design enables efficient parallel carrier transport, resulting in remarkable optoelectronic performance characterized by a high responsivity of 2933 A/W, an ultrahigh external quantum efficiency of 7.67 × 10⁵%, and a detectivity of 2.29 × 10¹² Jones. Furthermore, the device exhibited fast photoresponse characteristics, with fast response time of 52 ms and slow decay time of 2122 ms. More importantly, the device demonstrates superior synaptic plasticity with high learning retention of 6.58 μA and low forgetting rate of 0.073, as quantitatively described by the Wickelgren power-law model. Using the optoelectronic synaptic behavior of the device, we simulated learning and forgetting in neural networks, and achieved an accuracy of 92.5% on the MNIST handwritten digit data set. This work highlights the potential of NbOCl₂/α-In₂Se₃ heterostructures as a versatile platform for integrated optoelectronic systems, enabling intelligent sensing and neuromorphic computing.