Two‐dimensional (2D) materials are intensively attractive for fabricating high sensitive photodetectors in terms of atomically thin flexible and ultrafast charge transport feature. Due to their atomically thin body, designing high performance detector requires new physical mechanisms and device structures. In this review, we classify design strategies and device structures into four categories depending on their physical mechanisms (photovoltaic effect, photoconductive effect, photothermoelectric effect or photobolometric effect, and surface plasma‐ wave‐assisted effect), and summarize the device performances. Finally, future prospects and development direction for 2D material photodetectors are described. Those design strategies descriptions about photoelectronic detector provide a reference for high responsivity and fast response speed photodetector at broadband sensing in the future.

has been a challenge. [5,6] To enhance the absorption and photoresponse of graphene devices, researchers provide a series of strategies to interface graphene with light-absorbing semiconductors. [7][8][9][10][11][12][13][14][15][16] Early experimental studies on hybrid devices mainly focus on using one semiconductor layer, including colloidal quantum dots, [7,8] perov skites, [9] organic polymers, [10] single crystals, [16] 2D materials, [17] silicon, and other traditional materials. [11] More recently, improvement of device performance has been made by introducing PN junction bilayer absorbing layer. Incorporating graphene with a perovskite/ organic heterojunction or organic PN junction [14,15] is reported to improve both the photo responsivity and bandwidth. However, the limited narrow spectral range of light-absorbing layer causes ultrahigh photoconductive gain but at the same time sacrifices the detection spectral range. [18] In addition, a number of chemical approaches have been reported to synthesize the conjugated polymers/small molecules (typically with a bandgap of less than 1.6 eV) with appropriate energy gap and desirable photoelectric properties, but the device performance is still restricted. [19] So far the spectral range of graphene-based high gain photodetection is limited to typically 400-700 nm. [9,10,14,15,20,21] Herein, we explore a broadband (405-1550 nm) graphene/ organic semiconductor heterojunction phototransistors with bi-directional photoresponse (both positive and negative photocurrents) for the first time. Instead of broadening the absorption range of the semiconductor layer, our devices exploit ultrasensitive photoresponse at visible region, and the inverse photoresponse at near-infrared region without the need for cryogenics or adjusting gate voltage. Taking organic small molecule C 60 /pentacene heterojunction as the light-absorption layer, we achieve a highest responsivity of 9127 A W −1 , response time down to 275 µs, and external quantum efficiency up to 11.5% in visible regime and over 1800 A W −1 (0.063%) in near-infrared regime. Compared with previous work, our phototransistors not only have large built-in electric field at the C 60 /pentacene interface for high quantum efficiency, but also maintain an ultrasensitive response to the near-infrared region. The wavelength-dependent bi-directional response enables us to analyze the device mechanism. Our devices have potential applications in hyperspectral imaging.A graphene-semiconductor heterojunction is very attractive for realizing highly sensitive phototransistors due to the strong absorption of the semiconductor layer and the fast charge transport in the graphene. However, the photoresponse is usually limited to a narrow spectral range determined by the bandgap of the semiconductor. Here, an organic heterojunction (C 60 /pentacene) is incorporated on graphene to realize a broadband (405-1550 nm) phototransistor with a high gain of 5.2 × 10 5 and a response time down to 275 µs. The visible and near-infrared parts of the photor...

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.

Emerging graphene/organic phototransistors are eye-catching technologies owing to their unique merits including easy/low-cost fabrication, temperature independent, and achieving various functions. However, their development in the near-infrared (NIR) region is experiencing a bottleneck of inferior sensitivity due to low exciton dissociation efficiency and inefficient charge extraction rate. Here, a novel-design solution-processed graphene/organic NIR phototransistor is reported, that is, creatively introducing electron extraction layer of ZnO on graphene channel and employing organic ternary bulk heterojunction as photosensitive layer, successfully breaking that bottleneck. The phototransistor exhibits a high responsivity of 6.1 × 10 6 A W −1 , a superior detectivity of 2.4 × 10 13 Jones, and a remarkable minimum detection power of 1.75 nW cm −2 under 850 nm radiation. Considering its excellent NIR detection performance, a noncontact transmission-type pulse monitoring is carried out with no external circuit support, from which human pulse signal and heart rate can be displayed in real time. The phototransistor, interestingly, can be switched into a photomemory function with a retention time of 1000 s in the atmosphere through a gate voltage of −20 V. The design takes the characteristics of graphene/organic phototransistors to a higher level, beyond the limit of sensitivity, and opens up a novel approach for developing multifunction devices.

3D Dirac semimetal Cd3As2, as an ideal candidate photosensitive material, has attracted widespread attention due to its excellent characteristics of high carrier mobility and zero band gap. Although photodetector based on Cd3As2 crystal material has been made, there are still huge significances for the utilization of Cd3As2 thin film in commercial devices. In this paper, we demonstrated a wide-band photodetector based on heterojunction of Cd3As2 thin film and pentacene for the first time. This photodetector can detect the radiation wavelength from 450 nm (visible region) to 10600 nm (long wave infrared region) at room temperature, exhibiting high current responsivity (36.15 mA/W) and external quantum efficiency (7.29%) at 650 nm, of which R i is more than six times as high as previously reported that of crystalline Cd3As2 devices. Most interestingly, the far-infrared current responsivity of this detector at 10600 nm can reach 1.55 mA/W, which is extremely difficult for other 2D material detectors. Overall, the wide-wavelength photodetector based on the combined film using Cd3As2 and Pentacene is proved to possess superior performance for photodetector device application. Moreover, Cd3As2 thin film/pentacene heterojunction has an advantage in the manufacturing array devices, thus providing various possibilities for application of thin-film photodetector. The use of Cd3As2 thin film and organic molecules opens up a new path for the practical application of Cd3As2 materials.

Infrared upconversion devices (UCDs) enable low‐cost visualization of infrared optical signals without utilizing a readout circuit, which is of great significance for biological recognition and noninvasive dynamic monitoring. However, UCDs suffer from inferior photon to photon (p–p) efficiency and high turn‐on voltage (Von) for upconversion operation, hindering a further expansion in highly resolved infrared imaging. Herein, an efficient organic UCD integrating an interfacial exciplex emitter and a well‐designed near‐infrared (NIR) detector reveals a high efficiency up to 12.92% and a low Von down to 1.56 V. The low Von gives the capacity for detecting weak NIR light down to 3.2 µW cm–2, significantly expanding the detection power scale of UCDs. Thus, the imaging linear dynamic range (I‐LDR) is highly bias‐tunable, ranging from 13.23 to 84.4 dB. The high I‐LDR enables highly resolved and strong‐penetration bioimaging especially for thick biological sections, indicating great potential in noninvasive defect and pathological detection.

Nitrogen analogues of Chichibabin's and Müller's hydrocarbons exhibit small singlet–triplet energy gaps (ΔES–T from −1.05 to −1.27 kcal mol−1).

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.