Tunable Plasticity and Multilevel Photo-memory Enabled by Type-II Heterojunction in 2D Nanosheet-based Organic Optical Synapse

The rapid development of Internet of Things is driving advances in neuromorphic photonic computing systems, which leverage light for highly efficient and parallel information processing. Note that to achieve neuromorphic computing with artificial optical synapses, tunable synaptic plasticity and photo-memory functions enabled by direct optical modulation are essential. In this study, we design an organic optical synaptic device with two-dimensional (2D) metal oxide nanosheet as charge storage layer, demonstrating bimodal synaptic plasticity and multilevel photo-memory. The precise layer-by-layer liquid deposition technology enables direct integration 2D Cs2.7W11O351.3− nanosheet films with controllable thickness into the device for charge storage. Through interfacial band engineering, a type-II heterojunction is established between the organic semiconductor channel and the inorganic nanosheet, enabling gate-voltage-free photogenerated charge transfer and storage. Under optical modulation, the device exhibits the tunable synaptic behaviours ranging from short- to long-term plasticity and multilevel photo-memory capability with a retention time of 103 s. Then, we confirm the potential of the synaptic device for high-efficient neuromorphic computing, demonstrating a recognition capability with high accuracy of 97.8 %. Therefore, our devices shed new light on the development of optical computing systems.