Visible-Light-Responsive Organic Synaptic Devices Based on Rhodamine B-Doped Source-Gated Transistors

Organic artificial synaptic devices replicating biological neurons in sensing, transporting, and storing information with energy efficiency are gaining attention to next-generation computing circuits. Previous studies report that organic electrochemical transistors (OECTs) with polymeric semiconductors show inconsistent structure-synaptic properties. Also, OECTs with small molecular semiconductors demonstrate performance degradation by hydrophilic ions. This study develops low-power and high-performance organic photoneuromorphic devices based on n-type small molecular semiconductor of BPE-PTCDI doped with Rhodamine B (RhoB, an organic cationic dye) and a source-gated transistor (SGT) structure. Organic SGTs (OSGTs) with RhoB exhibit a high photoresponsivity of 2.07 × 10³ A W^–1 induced by charge transfer from RhoB in visible light and a low-power operation induced by the Schottky barrier. OSGTs exhibit 3.70 × 10³ times higher photoresponsivity per drive power (4.92 × 10⁸ A W^–2) than typical field-effect transistors. The OSGTs achieve synaptic properties at 1 V electrical pulsed stimulation by thinning the Schottky barrier of the SGT, high paired-pulse facilitation per driving power (3.20 × 10¹¹% W^–1), and pulsed photo-synaptic properties using hole trap by RhoB doping. These findings suggest potential technology for low-power auxiliary electronics for glaucoma patients and light trauma treatment and thus contribute to improving the quality of human life.