Optoelectronic synaptic devices, which combine the functions of photosensitivity and information processing, are essential for the development of artificial visual perception systems. Nevertheless, improving the paired pulse facilitation (PPF) index of optoelectronic synaptic devices, which is an urgent problem in the construction of high‐precision artificial visual perception systems, has received less attention so far. Herein, a light‐stimulated synaptic transistor (LSST) device with an ultra‐high PPF index (≈196%) is presented by introducing an ultra‐thin carrier regulator layer hexagonal boron nitride (h‐BN) into a classic graphene‐based hybrid transistor frame (graphene/CsPbBr3 quantum dots). Crucially, analysis of the rate‐limiting effect of h‐BN on photogenerated carriers reveals the mechanism behind the LSST ultra‐high PPF index. Furthermore, a two‐layer artificial neural network connected by LSST devices demonstrate ≈91.5% recognition accuracy of handwritten digits. This work provides an effective method for constructing artificial visual perception systems using a hybrid transistor frame in the future.
Light‐Stimulated Synaptic Transistors
Optoelectronic synaptic devices with a high paired pulse facilitation index are essential for constructing high‐precision artificial visual perception systems. In article number 2113053, Jun Wang and co‐workers develop a light‐stimulated synaptic transistor with an ultra‐high PPF index (≈196%) by introducing hexagonal boron nitride into a classic graphene‐based hybrid transistor framework, which provides an effective method for constructing artificial visual perception systems in the future.
The intriguing carrier dynamics in graphene heterojunctions have stimulated great interest in modulating the optoelectronic features to realize high-performance photodetectors. However, for most phototransistors, the photoresponse characteristics are modulated with an electrical gate or a static field. In this paper, we demonstrate a graphene/C60/pentacene vertical phototransistor to tune both the photoresponse time and photocurrent based on light modulation. By exploiting the power-dependent multiple states of the photocurrent, remarkable logical photocurrent switching under infrared light modulation occurs in a thick C60 layer (11 nm) device, which implies competition of the photogenerated carriers between graphene/C60 and C60/pentacene. Meanwhile, we observe a complete positive-negative alternating process under continuous 405 nm irradiation. Furthermore, infrared light modulation of a thin C60 (5 nm) device results in a photoresponsivity improvement from 3425 A/W up to 7673 A/W, and we clearly probe the primary reason for the distinct modulation results between the 5 and 11 nm C60 devices. In addition, the tuneable bandwidth of the infrared response from 10 to 3 × 103 Hz under visible light modulation is explored. Such distinct types of optical modulation phenomena and logical photocurrent inversion characteristics pave the way for future tuneable logical photocurrent switching devices and high-performance phototransistors with vertical graphene heterojunction structures.
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 × 10 6 A W −1 ), an outstanding respond speed (rise time/fall time is 20 µs/8.4 ms), and a remarkable detectivity (1.47 × 10 14 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 (10-10 7 nW 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.
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