Organic Source‐Gated Phototransistors with > 10⁴ Photo‐To‐Dark Current Ratio in the Visible Range at Zero Gate‐Source Bias

Abstract With growing interest in organic phototransistors, as not only sensors but also neuromorphic computing elements, the vast majority of research investigates structures comprising Ohmic source/drain contacts. Here, it is shown how source‐gated transistors (SGTs), in which a source contact barrier dominates electrical characteristics, can be implemented as phototransistors. Organic photo‐SGTs (OPSGTs) based on vacuum‐processed small‐molecule dinaphtho[2,3‐b:2′,3′‐f]thieno[3,2‐]thiophene (DNTT) demonstrate low saturation voltage, exceptional tolerance to channel length variation, and photo‐to‐dark current ratio (PDCR) peaks over 10⁶ for 819 µW broad spectrum incident light power. At zero gate‐source voltage, the PDCR reaches 10⁴, showing promise for simple sensor circuit implementation in medical and wellbeing applications.