Bidirectional Ultraviolet Photoresponsivity Synapses via Defect Engineering in Ultrathin D–A Conjugated Polymer Films for Advanced Artificial Vision Systems

Bidirectional photoresponsivity devices play an important role in visual information processing and visual computing. However, the heterojunction structure of conventional bidirectional photoresponsivity devices limits the diversity of material choices. This work presents a novel preparation method based on conjugated ultrathin polymer films, which introduces traps through the spin-coating of a low-concentration semiconductor solution onto a strongly hydrophobic substrate to form an ultrathin film to obtain devices exhibiting bidirectional photoresponsivity. The tunable bidirectional photoresponsivity enables the devices to successfully mimic biological synaptic behaviors such as excitatory postsynaptic currents (EPSC), inhibitory postsynaptic currents (IPSC), paired-pulse facilitation (PPF), and learning and forgetting behaviors. This work provides a new strategy for the preparation of all-optical artificial synapses that are suitable for practical applications that require large-scale processing. Finally, neural networks are used for image recognition, achieving a recognition rate of over 95%.