High-quality ultrathin single-crystalline SnSe2 flakes are synthesized under atmospheric-pressure chemical vapor deposition for the first time. A high-performance photodetector based on the individual SnSe2 flake demonstrates a high photoresponsivity of 1.1 × 10(3) A W(-1), a high EQE of 2.61 × 10(5)%, and superb detectivity of 1.01 × 10(10) Jones, combined with fast rise and decay times of 14.5 and 8.1 ms, respectively.

van der Waals (vdW) heterostructures based on atomically thin 2D materials have led to a new era in next-generation optoelectronics due to their tailored energy band alignments and ultrathin morphological features, especially in photodetectors. However, these photodetectors often show an inevitable compromise between photodetectivity and photoresponsivity with one high and the other low. Herein, a highly sensitive WSe /SnS photodiode is constructed on BN thin film by exfoliating each material and manually stacking them. The WSe /SnS vdW heterostructure shows ultralow dark currents resulting from the depletion region at the junction and high direct tunneling current when illuminated, which is confirmed by the energy band structures and electrical characteristics fitted with direct tunneling. Thus, the distinctive WSe /SnS vdW heterostructure exhibits both ultrahigh photodetectivity of 1.29 × 10 Jones (I /I ratio of ≈10 ) and photoresponsivity of 244 A W at a reverse bias under the illumination of 550 nm light (3.77 mW cm ).

2D SnS2 nanosheets have been attracting intensive attention as one potential candidate for the modern electronic and/or optoelectronic fields. However, the controllable large‐size growth of ultrathin SnS2 nanosheets still remains a great challenge and the photodetectors based on SnS2 nanosheets suffer from low responsivity, thus hindering their further applications so far. Herein, an improved chemical vapor deposition route is provided to synthesize large‐size SnS2 nanosheets, the side length of which can surpass 150 μm. Then, ultrathin SnS2 nanosheet‐based phototransistors are fabricated, which achieve high photoresponsivities up to 261 A W−1 (with a fast rising time of 20 ms and a falling time of 16 ms) in air and 722 A W−1 in vacuum, respectively. Furthermore, the effects of back‐gate voltage and air adsorbates on the optoelectronic properties of the SnS2 nanosheet have been systematically investigated. In addition, a high‐performance flexible photodetector based on SnS2 nanosheet is also fabricated with a high responsivity of 34.6 A W−1.

Van der Waals heterostructures (vdWHs) based on 2D layered materials with selectable materials properties pave the way to integration at the atomic scale, which may give rise to fresh heterostructures exhibiting absolutely novel physics and versatility. This feature article reviews the state-of-the-art research activities that focus on the 2D vdWHs and their optoelectronic applications. First, the preparation methods such as mechanical transfer and chemical vapor deposition growth are comprehensively outlined. Then, unique energy band alignments generated in 2D vdWHs are introduced. Furthermore, this feature article focuses on the applications in light-emitting diodes, photodetectors, and optical modulators based on 2D vdWHs with novel constructions and mechanisms. The recently reported novel constructions of the devices are introduced in three primary aspects: light-emitting diodes (such as single defect light-emitting diodes, circularly polarized light emission arising from valley polarization), photodetectors (such as photo-thermionic, tunneling, electrolyte-gated, and broadband photodetectors), and optical modulators (such as graphene integrated with silicon technology and graphene/hexagonal boron nitride (hBN) heterostructure), which show promising applications in the nextgeneration optoelectronics. Finally, the article provides some conclusions and an outlook on the future development in the field.WSe 2 /MoS 2 along the [001] zone axis in Figure 1c demonstrates that in this specific hetero-bilayer structure, the two hexagonal reciprocal lattices are rotated by 12.5° with respect to each layer without obvious lattice strain, resulting in moiré fringes with a spatial periodicity on the order of four to six times the lattice constants of each layer. [76] The atomically sharp interface of the heterostructure can be obtained by this stacking process confirmed by the high-resolution cross-sectional scanning transmission electron microscope image of the heterostructure (Figure 1d). Furthermore, the complex 2D vdWHs with more stacking layers can be realized by this mechanical transfer process.Mechanical transfer process provides a lot of flexibility in constructing diverse 2D vdWHs with various materials which may give rise to fresh physical properties, it is not scalable, which is imperative for further practical applications in electronics and optoelectronics. Alternatively, the bottom-up method such as direct CVD synthesis of 2D vdWHs has been successful in synthesizing graphene-or transition metal dichalcogenide (TMD)-based vdWHs, [77][78][79] which shows promising applications in scalable production. CVD GrowthCVD growth has shown booming development in the last decades such as the CVD growth of graphene [80,81] and TMDs, [82,83] and has been employed for synthesizing 2D vdWHs recently. [84] The most used method for CVD growth of 2D vdWHs is that evaporating the target sources such as WS 2 , WSe 2 , MoS 2 , MoSe 2 . Xu and co-workers [65] employed the mixture of WSe 2 and MoSe 2 powder as sources and obtained ...

Abstract2D GeSe possesses black phosphorous‐analog‐layered structure and shows excellent environmental stability, as well as highly anisotropic in‐plane properties. Additionally, its high absorption efficiency in the visible range and high charge carrier mobility render it promising for applications in optoelectronics. However, most reported GeSe‐based photodetectors show frustrating performance especially in photoresponsivity. Herein, a 2D GeSe‐based phototransistor with an ultrahigh photoresponsivity is demonstrated. Its optimized photoresponsivity can be up to ≈1.6 × 105 A W−1. This high responsivity can be attributed to the highly efficient light absorption and the enhanced photoconductive gain due to the existence of trap states. The exfoliated GeSe nanosheet is confirmed to be along the [001] (armchair direction) and [010] (zigzag direction) using transmission electron microscopy and anisotropic Raman characterizations. The angle‐dependent electric and photoresponsive performance is systematically explored. Notably, the GeSe‐based phototransistor shows strong polarization‐dependent photoresponse with a peak/valley ratio of 1.3. Furthermore, the charge carrier mobility along the armchair direction is measured to be 1.85 times larger than that along the zigzag direction.

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Electrochemically reversible redox couples that embrace more electron transfer at a higher potential are the eternal target for energy storage batteries. Here, we report a four-electron aqueous zinc-iodine battery by activating the highly reversible I2/I+ couple (1.83 V vs. Zn/Zn2+) in addition to the typical I−/I2 couple (1.29 V). This is achieved by intensive solvation of the aqueous electrolyte to yield ICl inter-halogens and to suspend its hydrolysis. Experimental characterization and modelling reveal that limited water activity and sufficient free chloride ions in the electrolyte are crucial for the four-electron process. The merits of the electrolyte also afford to stabilize Zn anode, leading to a reliable Zn-I2 aqueous battery of 6000 cycles. Owing to high operational voltage and capacity, energy density up to 750 Wh kg−1 based on iodine mass was achieved (15–20 wt% iodine in electrode). It pushes the Zn-I2 battery to a superior level among these available aqueous batteries.

An interesting in-plane anisotropic layered dimetal chalcogenide TaNiS is introduced, and the optical and electrical properties with respect to its in-plane anisotropy are systematically studied. The Raman vibration modes have been identified by Raman spectra measurements combined with calculations of phonon-related properties. Importantly, the TaNiS flakes exhibit strong anisotropic Raman response under the angle-resolved polarized Raman spectroscopy measurements. We found that Raman intensities of the A mode not only depend on rotation angle but are also related to the sample thickness. In contrast, the infrared absorption with light polarized along the a axis direction is always larger than that in the c axis direction regardless of thickness under the polarization-resolved infrared spectroscopy measurements. Remarkably, the first-principles calculations combined with angle-resolved conductance measurements indicate strong anisotropic conductivity of TaNiS. Our results not only prove TaNiS is a promising in-plane anisotropic 2D material but also provide an interesting platform for future functionalized electronic devices.