High‐Performance Phototransistor Based on Graphene/Organic Heterostructure for In‐Chip Visual Processing and Pulse Monitoring

Mimicking the real‐time sensing and processing capabilities of human retina opens up a promising pathway for achieving vision chips with high‐efficient image processing. The development of retina‐inspired vision chip also requires hardware with high sensitivity, fast image capture, and the ability to sense under various lighting conditions. Herein, a high‐performance phototransistor based on graphene/organic heterojunction is demonstrated with a superior responsivity (2.86 × 106 A W−1), an outstanding respond speed (rise time/fall time is 20 µs/8.4 ms), and a remarkable detectivity (1.47 × 1014 Jones) at 650 nm. The phototransistor combines weak‐light detection capability (minimum detectable light intensity down to 2.8 nW cm−2) with gate‐tunable bi‐directional photoresponse capable of simultaneously sensing and processing visual images for light intensities ranging over six orders magnitude (10–107nW cm−2). Moreover, the phototransistor also exhibits an intriguing feature undiscovered in other retina‐inspired devices, namely that it can real‐time monitor the human pulse signal and heart rate by using photoplethysmography technology, and the measured heart rate error is only 0.87% compared with a commercially available sensor. This study paves the way for the development of low‐light and bio‐signal sensitive artificial retinas in the future. In this work, a graphene/bulk heterojunction phototransistor is presented for applications as photodetector, vision sensor, and pulse sensor for the first time. The phototransistor has a gate‐tunable bi‐directional photoresponse for in‐chip image processing. Moreover, the phototransistor can monitor human pulse signal and heart rate in real time. This work paves the way for the future development of multifunction artificial retinas.