Ag Doping‐Mediated Bipolar Photoconductivity in 2D Bi 2 Se 3 Films for All‐Optically Programmed Synapse and Cryogenic Memory

All‐optically programmed optoelectronic synaptic devices (OESDs) exhibit significant application potential in vector‐matrix multiplication, optoelectronic logic gates, and optical communication. A key challenge in realizing all‐optically programmed OESDs is achieving persistent bipolar photoconductivity within a simple device architecture. In this work, we present Ag‐doped Ag@Bi 2 Se 3 films with wavelength‐dependent persistent positive and negative photoconductivity (PPC and NPC), achieving simple‐structured all‐optically programmed OESDs. This film is fabricated by chemical vapor deposition, followed by Ag particle decoration and annealing. This film‐based OESD exhibits persistent PPC and NPC, achieving long‐term synaptic weight potentiation under 405 nm illumination and depression at or above 520 nm wavelengths, which enables bipolar neuromorphic sensing. The simulation and experiment suggest that the NPC originates from the Ag doping‐induced band bending and a mobility gradient, which direct photo‐generated carriers toward the low‐mobility region, resulting in a reduction in conductance. Utilizing this OESD, simulations of handwritten digit recognition achieve an accuracy of 88.9% after 100 training epochs. Furthermore, this OESD demonstrates cryogenic retention. Following 520 nm pulsed illumination, the device retains 91.5% of the weight depression over 300 s. This work reveals a new strategy for designing simple all‐optically programmed synapses via doping engineering.