Two-dimensional material indium selenide (InSe) has offered a new platform for fundamental research in virtue of its emerging fascinating properties. Unlike 2H-phase transition-metal dichalcogenides (TMDs), ε phase InSe with a hexagonal unit cell possesses broken inversion symmetry in all the layer numbers, and predicted to have a strong second harmonic generation (SHG) effect. In this work, we find that the as-prepared pure InSe, alloyed InSe1–x Te x and InSe1–x S x (x = 0.1 and 0.2) are ε phase structures and exhibit excellent SHG performance from few-layer to bulk-like dimension. This high SHG efficiency is attributed to the noncentrosymmetric crystal structure of the ε-InSe system, which has been clearly verified by aberration-corrected scanning transmission electron microscopy (STEM) images. The experimental results show that the SHG intensities from multilayer pure ε-InSe and alloyed InSe0.9Te0.1 and InSe1–x S x (x = 0.1 and 0.2) are around 1–2 orders of magnitude higher than that of the monolayer TMD systems and even superior to that of GaSe with the same thickness. The estimated nonlinear susceptibility χ(2) of ε-InSe is larger than that of ε-GaSe and monolayer TMDs. Our study provides first-hand information about the phase identification of ε-InSe and indicates an excellent candidate for nonlinear optical (NLO) applications as well as the possibility of engineering SHG response by alloying.

Near infrared (NIR) photodetectors based on 2D materials are widely studied for their potential application in next generation sensing, thermal imaging, and optical communication. Construction of van der Waals (vdWs) heterostructure provides a tremendous degree of freedom to combine and extend the features of 2D materials, opening up new functionalities on photonic and optoelectronic devices. Herein, a type-II InSe/PdSe 2 vdWs heterostructure with strong interlayer transition for NIR photodetection is demonstrated. Strong interlayer transition between InSe and PdSe 2 is predicted via density functional theory calculation and confirmed by photoluminance spectroscopy and Kelvin probe force microscopy. The heterostructure exhibits highly sensitive photodetection in NIR region up to 1650 nm. The photoresponsivity, detectivity, and external quantum efficiency at this wavelength respectively reaches up to 58.8 A W −1 , 1 × 10 10 Jones, and 4660%. The results suggest that the construction of vdWs heterostructure with strong interlayer transition is a promising strategy for infrared photodetection, and this work paves the way to developing high-performance optoelectronic devices based on 2D vdWs heterostructures.

Achieving large‐sized and thinly layered 2D metal phosphorus trichalcogenides with high quality and yield has been an urgent quest due to extraordinary physical/chemical characteristics for multiple applications. Nevertheless, current preparation methodologies suffer from uncontrolled thicknesses, uneven morphologies and area distributions, long processing times, and inferior quality. Here, a sonication‐free and fast (in minutes) electrochemical cathodic exfoliation approach is reported that can prepare large‐sized (typically ≈150 µm2) and thinly layered (≈70% monolayer) NiPS3 flakes with high crystallinity and pure phase structure with a yield ≈80%. During the electrochemical exfoliation process, the tetra‐n‐butylammonium salt with a large ionic diameter is decomposed into gaseous species after the intercalation and efficiently expands the tightly stratified bulk NiPS3 crystals, as revealed by in situ and ex situ characterizations. Atomically thin NiPS3 flakes can be obtained by slight manual shaking rather than sonication, which largely preserves in‐plane structural integrity with large size and minimum damage. The obtained high quality NiPS3 offers a new and ideal model for overall water splitting due to its inherent fully exposed S and P atoms that are often the active sites for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Consequently, the bifunctional NiPS3 exhibits outstanding performance for overall water splitting.

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Indium selenide (InSe) has become a research hotspot because of its favorable carrier mobility and thickness-tunable band gap, showing great application potential in high-performance optoelectronic devices. The trend of miniaturization in optoelectronics has forced the feature sizes of the electronic components to shrink accordingly. Therefore, atomically thin InSe crystals may play an important role in future optoelectronics. Given the instability and ultralow photoluminescent (PL) emission of mechanically exfoliated ultrathin InSe, synthesis of highly stable mono- and few-layer InSe nanosheets with high PL efficiency has become crucial. Herein, ultrathin InSe nanosheets were prepared via thermal annealing of electrochemically intercalated products from bulk InSe. The size and yield of the as-prepared nanosheets were up to ∼160 μm and ∼70%, respectively, and ∼80% of the nanosheets were less than five layer. Impressively, the as-prepared nanosheets showed greatly enhanced stability and PL emission because of surface modification by carbon species. Efficient photoresponsivity of 2 A/W was achieved in the as-prepared nanosheet-based devices. These nanosheets were further assembled into large-area thin films with photoresponsivity of 16 A/W and an average Hall mobility of about 5 cm2 V–1 s–1. Finally, one-dimensional (1D) InSe nanoscrolls with a length up to 90 μm were constructed by solvent-assisted self-assembly of the exfoliated nanosheets.

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Originating from the breakthrough in discovering graphene (Gr), [1] 2D materials (2DMs) including transition metal dichalcogenide, [2,3] black phosphorous, [4] and others have been widely investigated in microscale photodetectors. By stacking multiple 2DMs into van der Waals (vdW) heterostructures, the photodetectors have demonstrated impressive 100 GHz highspeed response and 10 4 A W −1 highly sensitive photodetection performance. [5-7] Nonetheless, 2DM photodetectors usually response to broadband spectra located from ultraviolet to infrared light and exhibit linear dynamic ranges (LDRs) with merely several tens of decibels (dB) and less linearity, especially those who adopt photogating gain mechanism. [8-10] The dark current is reported from picoto microampere level, which corresponds to a current density from nA mm −2 to mA mm −2 level by considering the microscale photosensitive area of 2DM photodetectors. [11,12] It is much larger than that in commercial Si PIN photodetectors, which are generally below 100 pA mm −2. The high dark current also leads to a low on/ off ratio, which is not favorable in practical applications. Therefore, 2DM photodetectors have not met the demands in the next-generation Internet-of-Everything applications, such as artificial neural networks (ANN) image sensors, artificial retina, visible light communication (VLC), ultralowpower on-chip light interconnection, and flexible wearable devices, etc., which calls for filterless narrowband responses, wide LDRs, ultralow dark currents, and large on/off ratios. [13-19] 2D Ruddlesden-Popper-type organic-inorganic hybrid perovskites (2D-RPPs) are emerging light-harvesting and optoelectronic materials, which can be potential candidates to improve these performances. [20-22] 2D-RPPs are a family of organicinorganic hybrid perovskites (OIHPs), which share a similar corner-sharing octahedra network structure with 3D OIHPs (3DPs) as schematically illustrated in Figure 1a. [22,23] 3DPs have a general chemical formula of ABX 3 , where A is a monovalent organic cation [e.g., methylammonium (CH 3 NH 3 + , MA +)], B is a bivalent metal cation (e.g., Pb 2+ or Sn 2+), and X is a halide anion (e.g., Cl − , Br − , I −). An ABX 3 crystal consists of a network For next-generation Internet-of-Everything applications, for example, artificialneural-network image sensors, artificial retina, visible light communication, on-chip light interconnection, and flexible devices, etc., high-performance microscale photodetectors are in urgent demands. 2D material (2DM) photodetectors have been researched and demonstrated impressive performances. However, they have not met the demands in filterless narrowband photoresponse, wide linear dynamic range (LDR), ultralow dark current, and large on/off ratio, which are key performances for these applications. 2D Ruddlesden-Popper perovskites (2D-RPPs) are recently highlighted photovoltaic and optoelectronic materials. Embedding ultrathin 2D-RPPs into 2DM photodetectors holds potentials to improve these performances. Herein, a sin...

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