Kesterite Synaptic Memristor Towards Multilevel Physical Unclonable Functions Authorized Cloud Encryption and In‐Hardware Neural Activation for Neuromorphic Applications

High‐performance optoelectronic co‐modulated synaptic devices hold pivotal significance in advancing the practicalization of neuromorphic computing, yet challenges remain regarding their capacity to perform high‐level tasks in hardware neural networks. Herein, an optoelectronic synaptic memristor based on a kesterite heterostructure is innovatively proposed. The device enables precise regulation of carrier transport and resistive switching behaviors under dual light and electrical stimuli, achieving a high switching ratio of up to 10 4 , and allowing dynamic modulation of the switching window (2 × 10 2 ∼3 × 10 4 ) and switching voltage (0.16 ∼0.91 V) in a non‐contact manner. Furthermore, it faithfully emulates diverse bio‐synaptic functions, including excitatory postsynaptic current (EPSC), spike‐rate‐dependent plasticity (SRDP), multiparametric modulation of long‐term potentiation/depression (LTP/LTD), and brain‐like neuromorphic learning behaviors, manifesting superior bionic performance. Notably, this device supports two high‐level hardware applications: (1) a multi‐level authorized encryption computing framework relying on light/electrically induced physical unclonable functions (PUF) in memristors, suitable for secure cloud communications; (2) serving as neural network activation units for high‐performance complex pattern classification, outperforming its traditional software‐implemented counterparts. The results clarify the core potential of heterostructures in developing advanced multimodal synaptic memristors and provide a viable strategy toward next‐generation optoelectronic‐integrated neuromorphic systems.