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The discovery of novel materials with high gas sensing selectivity is a key driver of gas sensor technology. Based on the recently reported two-dimensional (2D) pentagonal BeP 2 , we introduce penta-BeAs 2 as a new member of the pentagonal family of materials for toxic gas sensors based on density functional theory (DFT). For electronic applications, a band structure calculation showed that penta-BeAs 2 has indirect band gaps of 0.38 and 0.79 eV, using GGA-PBE or HSE functionals. Stability analysis confirmed that penta-BeAs 2 is dynamically, mechanically, and thermally stable. The adsorption of toxic gases (CO, NO, and NO 2 ) and nontoxic gases (H 2 , N 2 , H 2 O, and CO 2 ) on the penta-BeAs 2 monolayer was studied. The contrasting adsorption behavior observed between toxic and nontoxic gases on penta-BeAs 2 (physisorption vs chemisorption) underscores its high selectivity for toxic gas-sensing applications. Adsorption energies for toxic gases fall within a moderate range (0.4-0.8 eV), indicating good reversibility and short recovery times at room temperature. Additionally, the quantum transport properties of penta-BeAs 2 were studied using the nonequilibrium Green's function (NEGF) approach, confirming strong sensitivity and selectivity toward toxic gases.

Self-healing functional materials can repair cracks and damage inside the battery, ensuring the stability of the battery material structure. This feature minimizes performance degradation during the charging and discharging processes, improving the efficiency and stability of the battery. Here, we have developed a novel healing conductive two-dimensional sulfur iodide (SI 4 ) composite cathode. This process integrates both sulfur and iodine compounds into carbon nanocages, forming a SI 4 @C core-shell structure. This cathode design improves electrical conductivity and repairability, facilitates rapid activation, and ensures structural integrity, resulting in a typical Na-SI 4 battery with high capacity and an exceptionally long cycle life. At 10.0 A g -1 , the capacity of the Na-SI 4 battery can still reach 217.4 mAh g -1 after more than 500 cycles, and the capacity decay rate per cycle is only 0.06%. In addition, the cathode exhibits a cascade redox reaction involving S and I, contributing to its high capacity. The in situ growth of a carbon shell further enhances the conductivity and structural robustness of the entire cathode. The flexibility and bendability of SI 4 @C-carbon cloth make it applicable for flexible electronic devices, providing more possibilities for battery design. The strategy of engineering a two-dimensional self-healing structure to construct a superior cathode is expected to be widely applied to other electrode materials. This study provides a new pathway for designing novel binary-conversion-type sodium-ion batteries with excellent long-term cycling performance.

Low-temperature large-area growth of two-dimensional (2D) transition-metal dichalcogenides (TMDs) is critical for their integration with silicon chips. Especially, if the growth temperatures can be lowered below the back-end-of-line (BEOL) processing temperatures, the Si transistors can interface with 2D devices (in the back end) to enable high-density heterogeneous circuits. Such configurations are particularly useful for neuromorphic computing applications where a dense network of neurons interacts to compute the output. In this work, we present low-temperature synthesis (400 °C) of 2D tungsten diselenide (WSe 2 ) via the selenization of the W film under ultrahigh vacuum (UHV) conditions. This simple yet effective process yields large-area, homogeneous films of 2D TMDs, as confirmed by several characterization techniques, including reflection high-energy electron diffraction, atomic force microscopy, transmission electron microscopy, and different spectroscopy methods. Memristors fabricated using the grown WSe 2 film are leveraged to realize a novel compact neuron circuit that can be reconfigured to enable homeostasis.

Recently, perovskite solar cells (PSCs) based on quasi-two-dimensional (quasi-2D) perovskites have drawn more attention due to their excellent stability, although their efficiencies are still lower than those of 3D ones. Here we applied post-treatment of 2D perovskite GAMA 5 Pb 5 I 16 (GA = guanidinium, MA = methylammonium) films with acetaminophen (AMP) to improve their performance. The efficiency of the solar cells with 2 mg/mL AMP post-treatment increased to 18.01% from 16.72% for those without post-treatment. The efficiency improvement results from the enlarged grain size, reduced trap state density, and better energy level matching after AMP post-treatment. In addition, the stability of the solar cells is improved. The solar cells with AMP post-treatment maintain 91% of the original power conversion efficiency value after aging for 30 days in the atmosphere. This work opens a new approach for the efficiency and stability enhancement of quasi-2D PSCs.

Due to the limited light absorption efficiency of atomic thickness layers and the existence of quenching effects, photodetectors solely made of transition metal dichalcogenides (TMDs) have exhibited an unsatisfactory detection performance. In this article, electret/TMD hybridized devices were proposed by vertically coupling a MoS 2 channel and the PTFE film, which reveals an optimized photodetection behavior. Negative charges were generated in the PTFE layer through the corona charging method, akin to applying a negative bias on the MoS 2 channel in lieu of a traditional voltage-driven back gate. Under a charging voltage of -6 kV, PTFE/MoS 2 devices reveal improved photodetection performance ( R hybrid = 67.95A/W versus R only = 3.37 A/W, at 470 nm, 1.20 mW cm -2 ) and faster recovery speed (τ d(hybrid) = 2000 ms versus τ d(only) = 2900 ms) compared to those bare MoS 2 counterparts. The optimal detection performance (2 orders of magnitude) was obtained when the charging voltage was -2 kV, limited by the minimum of the carrier density in MoS 2 channels. This study provides an alternative strategy to optimize optoelectronic devices based on the 2D components through non-voltage-driven gating.

Manipulation of the structure of covalent organic frameworks at the molecular level is an efficient strategy to shift their biological, physicochemical, optical, and electrical properties in the desired windows. In this work, we report on a new method to construct chiral triazine frameworks using metal-driven polymerization for enantiodiscrimination. The nucleophilic substitution reaction between melamine and cyanuric chloride was performed in the presence of PdCl 2 , ZnCl 2 , and CuCl 2 as chirality-directing agents. Palladium, with the ability of planar complex formation, was able to assemble monomers in two-dimensions and drive the reaction in two directions, leading to a two-dimensional triazine network with several micrometers lateral size. Nonplanar arrangements of monomers in the presence of ZnCl 2 and CuCl 2 , however, resulted in calix and bouquet structures, respectively. While 2D and bouquet structures showed strong negative and positive bands in the CD spectra, respectively, their calix counterparts displayed long-range weak negative bands. In spite of the ability of both calix and bouquet networks to load l-histidine 35 and 50% more than d-histidine from pure enantiomers, respectively, only calix counterparts were able to take up this enantiomer (78%) from the racemic mixture. The two-dimensional polytriazine network did not show any specific interactions with pure enantiomers or their racemic mixtures.

Magnetic tunnel junctions (MTJs) based on van der Waals (vdW) heterostructures with sharp and clean interfaces on the atomic scale are essential for the application of next-generation spintronics. However, the lack of room-temperature intrinsic ferromagnetic crystals with perpendicular magnetic anisotropy has greatly hindered the development of vertical MTJs. The discovery of room-temperature intrinsic ferromagnetic two-dimensional (2D) crystal Fe 3 GaTe 2 has solved the problem and greatly facilitated the realization of practical spintronic devices. Here, we demonstrate a room-temperature MTJ based on a Fe 3 GaTe 2 /WS 2 /Fe 3 GaTe 2 heterostructure for the first time. The tunneling magnetoresistance (TMR) ratio is up to 213% with a high spin polarization of 72% at 10 K, the highest ever reported in Fe 3 GaTe 2 -based MTJs up to now. A tunneling spin-valve signal robustly persists at room temperature (300 K) with a bias current down to 10 nA. Moreover, the spin polarization can be modulated by bias current and the TMR shows a sign reversal at a large bias current. Our work sheds light on the potential application of low-energy consumption in all-2D vdW spintronics and offers alternative routes for the electronic control of spintronic devices.

Two-dimensional (2D) siloxene (Si 6 O 3 H 6 ) has shown promise as a negative electrode material for Li-ion batteries due to its high gravimetric capacity and superior mechanical properties under (de)lithiation compared to bulk Si. In this work, we prepare purified siloxene nanosheets through the removal of bulk Si contaminants, use ultrasonication to control the lateral size and thickness of the nanosheets, and probe the effects of the resulting morphology and purity on the electrochemistry. The thin siloxene nanosheets formed after 4 h of ultrasonication deliver an average capacity of 810 mA h/g under a 1000 mA/g rate over 200 cycles with a capacity retention of 76%. Interestingly, the purified siloxene shows lower initial capacity but superior capacity retention over extended cycling. The 2D morphology benefit is illustrated where the parent siloxene nanosheet morphology and structure were largely maintained based on operando optoelectrochemistry, in situ Raman, ex situ scanning electron microscopy, and ex situ transmission electron microscopy. Furthermore, the purified siloxene-based electrode free from crystalline Si impurity experiences the least expansion upon (de)lithiation as visualized by cross-section electron microscopy of samples recovered post-cycling.

A two-dimensional silicon nanosheet (2D Si NS) is promising as a lithium-ion battery anode. However, insufficient cycling life at high current density hampers its practical applications due to its easy fragileness. Rationally engineering the Si micro/nanostructure is promising to address this issue. Unfortunately, the precise construction of a dedicated micro/nanostructure into 2D Si NS meets serious challenges. Herein, a facile strategy is developed to synthesize a sandwich-like honeycomb Si NS/solid Si NS/honeycomb Si NS (h/s/h-Si NS) anode through self-assembled preparation of a sandwich-like honeycomb SiO 2 NS/solid SiO 2 NS/honeycomb SiO 2 NS template, followed by magnesiothermic reduction. This unique structure effectively enhances the mechanical strength, enlarges the specific surface area, and reserves sufficient space to accommodate the anode volume change. A conductive carbon layer is further coated on the h/s/h-Si NS (h/s/h-Si@C NS) to construct a stable electrode/electrolyte interface. The optimal h/s/h-Si@C NS displays outstanding performance with high initial Coulombic efficiency (86%), high reversible capacity (1624 mAh g -1 after 100 cycles at 1000 mA g -1 ), good rate capability (over 1000 mAh g -1 at 4000 mA g -1 ), and long cycling life even at 4000 mA g -1 (93% retained capacity after 1000 cycles). This work provides a new strategy for constructing high-performance Si electrodes for lithium-ion battery applications.

Exploring the depolymerization strategy of liposoluble luminophores in the aqueous phase is vital for the development of electrochemiluminescence (ECL). In this work, tetraoctylammonium bromide (TOAB) with four long hydrophobic chains and short hydrophilic ends is used as a template to limit the aggregation of benzimidazole (BIM). By adjusting the loading of BIM on the hydrophobic chains of TOAB, a two-dimensional lamellar BIM/TOAB is formed, the ECL intensity of which is 6.4 times higher than that of the aggregated BIM (H 2 O 2 as the coreactant). In terms of ECL spectroscopies, cyclic voltammetry , ECL transients, and the adjustment of the scanning potential range, the ECL mechanism is thoroughly studied. This work provides a new way to depolymerize organic luminophores and reveals a possible pathway in the annihilation ECL mechanism.

Two-dimensional (2D) Dion-Jacobson (DJ) perovskites are drawing significant attention in optoelectronic fields because of their enhanced out-of-plane electron coupling and improved structure stability. However, the structural effects of organic cations on the in-plane charge transport properties of 2D DJ lead bromide perovskites have remained less explored. Herein, we adopt asymmetric 3-(dimethylamino)-1-propylammonium (DMPD) and symmetric butane-1,4-diammonium (BDA) to systematically investigate the influence of organic cations on the structural, optical, and in-plane charge transport properties of 2D lead bromide perovskites. The large penetration depth of DMPD 2+ induces a decreased perovskite layer distortion and a lower bandgap in DMPDPbBr 4 , compared with that of BDAPbBr 4 . Moreover, DMPDPbBr 4 is shown to possess a low exciton binding energy, a low defect density, and a low ion migration activation energy, thereby yielding a more efficient in-plane charge collection efficiency than BDAPbBr 4 . Density functional theory calculations suggest that the improved in-plane charge transport can be traced to the enlarged antibonding coupling between Pb-6s and Br-4p orbitals that enables a high band dispersion and a low carrier effective mass in the in-plane direction of DMPDPbBr 4 . Finally, the planar Ag/DMPDPbBr 4 /Ag photodetector delivers a satisfying detectivity of 1.73 × 10 12 Jones under an incident power intensity of 0.16 mW cm -2 and a high on/off ratio of 5.3 × 10 3 . The above findings offer novel insight for the design of 2D DJ lead bromide perovskites for optoelectronic devices.

The rational design of ferromagnetic materials is crucial for the development of spintronic devices. Using first-principles structural search calculations, we have identified 73 two-dimensional transition metal hydrides. Some of them show interesting magnetic properties, even when combined with the characteristics of the electrides. In particular, the P 3̅ m 1 Fe 2 H monolayer is stabilized in a 1T-MoS 2 -type structure with a local magnetic moment of 3 μ B per Fe atom, whose robust ferromagnetism is attributed to the exchange interaction between neighboring Fe atoms within and between sublayers, leading to a remarkably high Curie temperature of 340 K. On the other hand, it has a large magnetic anisotropic energy and spin-polarization ratio. Interestingly, the above room-temperature ferromagnetism of the Fe 2 H monolayer is well preserved within a biaxial strain of 5%. The structure and electron property of surface-functionalized Fe 2 H are also explored. All of these interesting properties make the Fe 2 H monolayer an attractive candidate for spintronic nanodevices.

Photocatalytic N 2 fixation has emerged as one of the most useful ways to produce NH 3 , a useful asset for chemical industries and a carbon-free energy source. Recently, significant progress has been made toward designing efficient photocatalysts to achieve this objective. Here, we introduce a highly active type-II heterojunction fabricated via integrating two-dimensional (2D) nanosheets of exfoliated g-C 3 N 5 with nickel-chromium layered double hydroxide (NiCr-LDH). With an optimized loading of NiCr-LDH on exfoliated g-C 3 N 5 , excellent performance is realized for green ammonia synthesis under ambient conditions without any noble metal cocatalyst(s). Indeed, the g-C 3 N 5 /NiCr-LDH heterostructure with 2 wt % of NiCr-LDH (CN-NCL-2) exhibits an ammonia yield of about 2.523 mmol/g/h, which is about 7.51 and 2.86 times higher than that of solo catalysts, i.e., NiCr-LDH (NC-L) and exfoliated g-C 3 N 5 (CN-5), respectively, where methanol is used as a sacrificial agent. The enhancement of NH 3 evolution by the g-C 3 N 5 /NiCr-LDH heterostructure can be attributed to the efficient charge transfer, a key factor to the photocatalytic N 2 fixation rate enhancement. Additionally, N 2 vacancies present in the system help adsorb N 2 on the surface, which improves the ammonia production rate further. The best-performing heterostructure also shows long-term stability with the NH 3 production rate remaining nearly constant over 20 h, demonstrating the excellent robustness of the photocatalyst.

Nanopatterns at near atomic dimensions with controllable quantum dot states (QDSs) are promising candidates for the continued downscaling of electronic devices. Herein, we report a phase transition-induced QD system achieved on the √3 × √3-Bi/Si(111) surface reconstruction, which points the way to a novel strategy on QDS implementation. Combining scanning tunneling microscopy, scanning tunneling spectroscopy, and density functional theory (DFT) calculations, the structure, energy dispersion, and size effect on band gap of the QDs are measured and verified. As-created QDs can be manipulated with a dot size down to 2 nm via Bi phase transformation, which, in turn, is triggered by thermal annealing at 700 K. The transition mechanism is also supported by our DFT calculations, and an empirical analytical model is developed to predict the transformation kinetics.

Synthesizing layered transition-metal carbides, MXenes, with a mesoporous structure remains challenging but is highly useful because it converts the laminated two-dimensional structures into versatile porous materials. Hydrogen bonds between intercalated H 2 O molecules and oxygen terminal groups on the surface are formed in aqueous solution processes, and this is a determining factor of surface area. We developed an extraction method to remove intercalated water molecules based on a simple intermolecular force attraction strategy in a co-solvent system using a combination of polar-protic/-aprotic and non-polar solvents. As a result, self-aggregated mesoporous Ti 3 C 2 T x was realized without any additives. The dipole-dipole interaction between H 2 O and CHCl 3 molecules under non-polar solvent conditions assists the extraction of intercalated H 2 O from the MXene suspension, which can form a self-aggregated morphology (not re-stacked horizontally). The process yields Ti 3 C 2 T x with a layered structure of embedded mesopores and a specific surface area that is 13-fold higher than that of standard MXene. Electrodes made with the resulting MXene exhibited a larger specific capacitance of 224 F/g (1 A/g), with an improved cyclic retention of 96.4%@10,000 cycles. This intermolecular attraction-induced approach, involving the manipulation of morphology, is simple to mass-produce and can be used for MXene-based electrochemical applications.

Despite the high capacity and low cost of lithium-sulfur (Li-S) batteries, their commercialization is greatly blocked by multiple bottlenecks including the shuttle effect of lithium polysulfides (LiPSs), poor conductivity of sulfur, and sluggish reaction kinetics. Herein, we propose novel two-dimensional MSi 2 P 4 (M = V, Nb, and Ta) monolayers as promising sulfur hosts to improve the Li-S battery performance. Our calculations show that MSi 2 P 4 monolayers offer moderate binding strengths to the polysulfides, which are expected to effectively inhibit the LiPS shuttling and dissolution. Moreover, the conductive properties of the MSi 2 P 4 systems are well maintained after LiPS adsorption, eliminating the insulating nature of sulfur species. Remarkably, MSi 2 P 4 monolayers exhibit superior electrocatalytic activity for the sulfur reduction reaction and the Li 2 S decomposition reaction, which considerably lowers the energy barriers of LiPS conversions during discharge and charge, thus ensuring the fast redox kinetics and high sulfur utilization of Li-S batteries. This study pioneers the application of MSi 2 P 4 monolayers as highly efficient sulfur host materials for Li-S batteries and affords insights for further development of advanced Li-S batteries.

Exploring high performance and excellent ambient stability in two-dimensional (2D) monolayer photoelectric materials is motivated by not only practical applications but also scientific interest. Here, a new 2D monolayer W 8 Se 12 structure is synthesized via in situ electron-beam irradiation on 2D WSe 2 . Moreover, we systematically studied the photoelectric properties of the class of monolayer M 8 X 12 (M = Mo, W; X = S, Se, and Te) materials by first principles. The results indicated that Mo 8 S 12 , Mo 8 Se 12 , W 8 S 12 , and W 8 Se 12 monolayers possess desirable direct band gaps and remarkable anisotropic optical absorption in visible light, while Mo 8 Te 12 and W 8 Te 12 monolayers are metals. Impressively, the monolayer W 8 Se 12 can result in a direct-indirect-metal transition under uniaxial strain. In addition, they show high anisotropic carrier mobilities (up to 10 4 cm 2 V -1 s -1 ), significantly over those of transition-metal dichalcogenides. These new binary monolayer M 8 X 12 structures can effectively broaden the 2D material family and may provide four potential candidates in photoelectric applications.

Two-dimensional (2D) multilayer Dion-Jacobson (DJ) phase organic inorganic hybrid perovskites (OIHPs) have attracted extensive research attention due to the high stability and excellent charge-transport properties in the optoelectronic field. However, the synthesis of 2D multilayer DJ OIHPs is still very challenging. Until now, only few multilayer DJ perovskites have been reported and most of them are based on volatile methylamine (MA) cations. Compared with MA-based OIHPs, the OIHPs constructed with formamidinium (FA) as perovskitizers not only improve the stability but also extend the light absorption range. Meanwhile, the introducing aromatic diamines as spacers could promote the electron-hole separation in such DJ hybrids. However, the DJ OIHP bulk single crystal constructed by using the advantages of FA as perovskitizers and aromatic diamines as spacers is still blank. Herein, we integrate the properties of organic cations and inorganic skeletons at a molecular-scale to construct a broadband-responsive 2D bilayer DJ perovskite (3AMPY)(FA)Pb 2 I 7 [3AMPY = 3-(aminomethyl)pyridinium], which shows a fascinating detectivity from X-ray (5.23 × 10 4 μC Gy air -1 cm -2 at 200 V bias) and visible light (6 × 10 12 jones at 637 nm) to the near-infrared region (2.6 × 10 9 jones at 780 nm). After an in-depth analysis of structure and optical properties, we found that the distortion degree of Pb-I-Pb bond angles between adjacent PbI 6 octahedra plays a crucial role on optical properties; on the other hand, the interlayer spacer cations (3AMPY) and intralayer perovskitizers (FA) mutual participate in the contribution of the conduction band, making (3AMPY)(FA)Pb 2 I 7 have a narrow optical band gap of 1.54 eV. Such a 2D perovskite material with a wide spectra response will be the preferred choice for photodetection under complex conditions.

Owing to the durable environmental stability and tunable photophysical properties of the two-dimensional Ruddlesden-Popper (2D RP) perovskite, it has a great potential in stable perovskite solar cells (pero-SCs). However, almost efficient 2D RP pero-SCs are prepared by the hot-casting or anti-solvent assisted spin-coating method, which greatly limits their applications. Herein, a multifunctional strategy through introducing a novel organic salt, benzimidazolium iodide (BnI), as a spacer and KI as an additive is reported to successfully fabricate a high-quality Bn-based 2D RP perovskite film in the hot-casting and anti-solvent free spin-coating method. The entire conjugated backbone of benzimidazolium is expected to enhance charge carrier transport within the 2D RP perovskite film. And KI can lead to a preferred orientation and less defects in the 2D RP perovskite film. Then, a maximum power conversion efficiency (PCE) of 15.12% is obtained, which is the highest performance for 2D RP perovskite devices without the hot-casting or anti-solvent method. The unsealed device maintains 92.1% of its original performance when kept in air (40-45% relative humidity) for 720 h and 87.9% of the initial performance after 528 h of heating at 85 °C.

Magnetic tunnel junctions (MTJs), ferroelectric/antiferroelectric tunnel junctions (FTJs/AFTJs), and multiferroic tunnel junctions (MFTJs) have recently attracted significant interest for technological applications of nanoscale memory devices. Until now, most of them are based on perovskite oxide heterostructures with a relatively high resistance-area (RA) product and low resistance difference unfavorable for practical applications. The recent discovery of the two-dimensional (2D) van der Waals (vdW) ferroelectric (FE) and magnetic materials has opened a new route to realize tunnel junctions with high performance and atomic-scale dimensions. Here, using first-principles calculations, we propose a new type of 2D tunnel junction: an antiferroelectric magnetic tunnel junction (AFMTJ), which inherits the features of both MTJ and AFTJ. This AFMTJ is composed of monolayer CuInP 2 S 6 (CIPS) sandwiched between 2D magnetic electrodes of CrSe 2 . The AFTJ with nonmagnetic electrodes of TiSe 2 on both sides of CIPS and the asymmetric AFTJ with both CrSe 2 and TiSe 2 electrodes are also investigated. Based on quantum-mechanical modeling of the electronic transport, sizeable tunneling electroresistance effects and multiple nonvolatile resistance states are demonstrated. More importantly, a remarkably low RA product (less than 0.1 Ω·μm 2 ) makes the proposed vdW AFMTJs superior to the conventional MFTJs in terms of their promising nonvolatile memory applications. Our calculations provide new guidance for the experiment and application of nanoscale memory devices.

In recent years, two-dimensional (2D) magnetic heterostructures have captured widespread interest as they provide a fertile ground for exploring the novel properties induced by interfacial magnetic coupling, modulating the intrinsic magnetism of the 2D magnet, and exploiting new spintronic device applications. In this Spotlight on Applications, dominating synthetic strategies employed to fabricate 2D magnetic heterostructures are introduced first. Notably, we then concentrate on two different kinds of magnetic interfaces, namely, the magnetic-nonmagnetic interface and the magnetic-magnetic interface. Specifically, various interface modulated magnetisms such as valley splitting and the anomalous Hall effect as well as their related device applications such as magnetic tunnel junctions have been further reviewed and discussed. Finally, we briefly summarize the recent progress of 2D magnetic heterostructures and outline the future development direction of this booming field.

Recently, excitonic solar cells (XSCs) with high photovoltaic performance have raised research interests because of their high power conversion efficiencies (PCEs). Herein, by using first-principles calculations, we predict that γ-BX (X = S, Se, Te) monolayers are direct semiconductors with the band gaps of 2.94, 2.71, and 1.32 eV, respectively, and maintain semiconduction in the broad strain range of 0% ≤ δ ≤ 5%. The moderate direct band gap, high transport property, dramatically high absorption from visible to the ultraviolet region, and extraordinary excitonic behavior of monolayer γ-BTe, render it promising for next-generation optoelectronic and photovoltaic devices. By choosing monolayer GeP 2 as a proper acceptor material, the practical upper limit of PCE for the heterobilayers of γ-BTe/GeP 2 reaches up to 21.76% (22.95% under strain), comparable to typical heterobilayer solar cells, making it a competitive donor material for photovoltaic device applications.

Various strategies have been developed to mitigate the huge volume expansion of a silicon-based anode during the process of (de)lithiation and accelerate the transport rate of the ions/electrons for lithium-ion batteries (LIBs). Here, we report a one-step synthetic route through a low-temperature eutectic molten salt (LiCl-KCl, 352 °C) to fabricate two-dimensional (2D) silicon-carbon hybrids (Si@SiO x @MpC), in which the silicon nanoparticles (SiNPs) with an ultrathin SiO x layer are fully encapsulated by graphene-like carbon nanosheets derived from a low-cost mesophase pitch. The combination of an amorphous graphene-like carbon conductive matrix and a SiO x protective layer strongly promotes the electrical conductivity, structure stability, and reaction kinetics of the SiNPs. Consequently, the optimized Si@SiO x @MpC-2 anode delivers large reversible capacity (1239 mAh g -1 at 1.0 A g -1 ), superior rate performance (762 mAh g -1 at 8 A g -1 ), and long cycle life over 600 cycles (degradation rate of only 0.063% every cycle). When coupled with a homemade nano-LiFePO 4 cathode in a full cell, it exhibits a promising energy density of 193.5 Wh kg -1 and decent cycling stability for 200 cycles at 1C. The methodology driven by salt melt synthesis paves a low-cost way toward simple fabrication and manipulation of silicon-carbon materials in liquid media.

Compared with single-component metal oxides, multicomponent metal oxides show good gas sensing performance in the field of gas sensing, but they still need to be further improved in terms of rapid response. In this paper, a two-dimensional flaky WO 3 /Bi 2 W 2 O 9 composite material with a thickness of about 32.3 nm was synthesized by a simple solvothermal method. The composite has good sensing performance and selectivity toward H 2 S. When the operating temperature is as low as 92 °C, the response to 100 ppm H 2 S reaches 84.18, and the response time is 2 s, which is extremely fast due to the open system of the two-dimensional nanosheet. A combination of gas chromatography-mass spectrometry (GC-MS) and X-ray photoelectron spectroscopy (XPS) is used to analyze the changes of H 2 S and the surface chemistry of WO 3 /Bi 2 W 2 O 9 composite materials; the sensing mechanism of H 2 S was studied by a Kelvin probe and UV diffuse reflection. Compared with the pure phase WO 3 and Bi 2 W 2 O 9 , good gas sensing properties of the WO 3 /Bi 2 W 2 O 9 composite may be due to its unique heterostructure. This is the first application of WO 3 /Bi 2 W 2 O 9 in the field of gas sensing and is of great significance for the rapid detection of H 2 S at low temperatures for multicomponent metal oxides.

Currently, two-dimensional materials are being actively pursued in catalysis and other fields due their abundance of defects, which results in enhanced performance relative to their bulk defect-free counterparts. To date, the exploitation of defects in two-dimensional materials to enhance photothermal therapies has received little attention, motivating a detailed investigation. Herein, we successfully fabricated a series of novel CoFe-based photothermal agents (CoFe- x ) by heating CoFe-layered double hydroxide (CoFe-LDH) nanosheets at different temperatures ( x ) between 200-800 °C under a Ar atmosphere. The CoFe- x products differed in their particle size, cobalt defect concentration, and electronic structure, with the CoFe-500 product containing the highest concentration of Co 2+ defects and most efficient photothermal performance under near-infrared (NIR, 808 nm) irradiation. Experiments and density functional theory (DFT) calculations revealed that Co 2+ defects modify the electronic structure of CoFe- x , narrowing the band gap and thus increasing the nonradiative recombination rate, thereby improving the NIR-driven photothermal properties. In vitro and in vivo results demonstrated that CoFe-500 was an efficient agent for photothermal cancer treatment and also near-infrared (NIR) thermal imaging, magnetic resonance (MR) imaging, and photoacoustic (PA) imaging. This work provides valuable new insights about the role of defects in the rational design of nanoagents with optimized structures for improved cancer therapy.

Promoting the formate oxidation reaction (FOR) is central to develop promising direct formate fuel cells, but current electrocatalysts are suffering from low activity and ultrapoor stability. Herein, the ternary PdAgRh nanoalloys with ultrathin two-dimensional architecture are for the first time synthesized and employed as a novel class of electrocatalysts for the FOR. Benefitting from unique nanostructure as well as oxophilic Rh surface oxides, the Pd 55 Ag 30 Rh 15 /C electrocatalyst demonstrates an exceptional FOR activity of 1.85 A mg Pd -1 , showing a 4.74-fold improvement compared to the commercial Pd/C, and retains the current density of 150 mA mg Pd -1 after a long-term test, representing the greatest durability among all available FOR electrocatalysts. More strikingly, extending the upper limit potential (ULP) of cyclic voltammetry is revealed to facilitate the surface reconstruction of the Pd 55 Ag 30 Rh 15 /C electrocatalyst to in situ form Ag surface oxides (Ag-O), resulting in a highly active and stable Pd/Ag-O interface at the atomic scale, which considerably boost the FOR performance. In particular, the reconstructed Pd 55 Ag 30 Rh 15 /C electrocatalyst exhibits a mass activity of 3.26 A mg Pd -1 with 74.2% of initial activity retained after 1000 cycles. This work showcases an effective strategy to tune surface reconstruction on multimetallic nanoalloys for robust FOR electrocatalysts and beyond.

Lots of research studies reveal that the surface atoms on the top/bottom facets of the nanosheets are the key features in enhancing electrocatalytic activity while the edge and corner sites of electrocatalysts often possess superior activity. Herein, we report 2D dendritic PdAgPt ternary nanoalloys with abundant crystal defects such as steps, twin boundary, and atomic holes, which can effectively work as catalytic active-sites. The morphology of PdAgPt nanoalloys can be regulated readily from dendritic nanosheets to nanowheels. Compared with binary Pd 68 Ag 32 nanodendrites, Pd 62 Pt 38 nanospheres, and Pt/C catalyst, the composition- and morphology-optimized Pd 43 Ag 21 Pt 36 nanowheels exhibit the best mass/specific activity and stability for methanol/ethanol oxidation reaction (MOR/EOR). The mass peak current density for EOR/MOR of Pd 43 Ag 21 Pt 36 is 7.08/3.50 times of the Pt/C catalyst. Simultaneously, the hydrogen evolution reaction performance of the Pd 43 Ag 21 Pt 36 nanowheels in terms of the lowest overpotential of 9 mv at a current density of 10 mA/cm 2 and high electrochemical stability is much better than that of binary Pd 68 Ag 32 nanodendrites, Pd 62 Pt 38 nanospheres, and Pt/C.

We investigate the role of growth temperature and metal/chalcogen flux in atmospheric pressure chemical vapor deposition growth of MoSe 2 and WSe 2 on Si/SiO 2 substrates. Using scanning electron microscopy and atomic force microscopy, we observe that the growth temperature and transition metal flux strongly influence the domain morphology, and the compact triangular or hexagonal domains ramify into branched structures as the growth temperature (metal flux) is decreased (increased). The competition between adatom attachment to the domain edges and diffusion of adatoms along the domain boundary determines the evolution of the observed growth morphology. Depending on the growth temperature and flux, two different branched structures-fractals and dendrites-grow. The fractals (with a dimension of ∼1.67) obey a diffusion-limited aggregation mechanism, whereas the dendrites with a higher fractal dimension of ∼1.80 exhibit preferential growth along the symmetry-governed directions. The effect of chalcogen environment is studied, where a Se-rich condition helps restrict Mo-rich nucleus formation, promoting lateral growth. For a Se-deficient environment, several multilayer islands cluster on two-dimensional domains, suggesting a transition from lateral to vertical growth because of insufficient Se passivation. X-ray photoelectron spectroscopy analysis shows a near perfect stoichiometry (Mo/Se = 1:1.98) of MoSe 2 grown in a Se-rich environment, whereas in the Se-deficient condition, a ratio of Mo/Se = 1:1.68 is observed. This also supports the formation of metal-rich nuclei (Mo 1+ x Se 2- x ) under Se-deficient conditions, leading to three-dimensional clustering. Tuning the growth temperature and metal/chalcogen flux, we propose an optimized CVD growth window for synthesizing large-area Mo(W) selenide.

Tandem solar cells (SCs) connecting two subcells with different absorption bands have the potential to reach the commercialized photovoltaic standard. However, the performance improvement of tandem architectures is still a challenge, primarily owing to the mismatch of band gaps in two subcells. Here, we demonstrate a two-dimensional (2D) BAs/InTe-based tandem SC, which could achieve solar-to-electric conversion efficiency higher than 30%. First, the narrow band gap of hexagonal single-layer BX (X = P and As) and wide band gap of single-layer YZ (Y = Ga and In, Z = S, Se, and Te) are found to have high thermodynamic stability based on density functional theory calculations. Next, considering narrow and wide band gaps at the HSE06 functional, single-layer BX/YZ-based tandem SCs are built to effectively capture a broad-band solar spectrum by combining such two subcells. Since the band gap of single-layer BAs matches well with that of the InTe monolayer, the power conversion efficiency of BAs/InTe-based tandem SC can reach as high as 30.2%. Moreover, it is important to note that the used materials, including few-layer GaZ and InSe, have been experimentally prepared, which strongly supports the high feasibility of the designed 2D tandem SCs in this work. Our constructed 2D-material-based devices can be competitive in realizing commercialized high-performance tandem SCs.

Electric double-layer (EDL) gating using a custom-synthesized polyester single-ion conductor (PE400-Li) is demonstrated on two-dimensional (2D) crystals for the first time. The electronic properties of graphene and MoTe 2 field-effect transistors (FETs) gated with the single-ion conductor are directly compared to a poly(ethylene oxide) dual-ion conductor (PEO:CsClO 4 ). The anions in the single-ion conductor are covalently bound to the backbone of the polymer, leaving only the cations free to form an EDL at the negative electrode and a corresponding cationic depletion layer at the positive electrode. Because the cations are mobile in both the single- and dual-ion conductors, a similar enhancement of the n-branch is observed in both graphene and MoTe 2 . Specifically, the single-ion conductor decreases the subthreshold swing in the n-branch of the bare MoTe 2 FET from 5000 to 250 mV/dec and increases the current density and on/off ratio by two orders of magnitude. However, the single-ion conductor suppressed the p-branch in both the graphene and the MoTe 2 FETs, and finite element modeling of ion transport shows that this result is unique to single-ion conductor gating in combination with an asymmetric gate/channel geometry. Both the experiments and modeling suggest that single-ion conductor-gated FETs can achieve sheet densities up to 10 14 cm -2 , which corresponds to a charge density that would theoretically be sufficient to induce several percent strain in monolayer 2D crystals and potentially induce a semiconductor-to-metal phase transition in MoTe 2 .

Lead halide perovskites are emerging as promising candidates for high-efficiency light-emitting diode (LED) applications because of their tunable band gaps and high quantum yield (QY). However, it remains a challenge to obtain stable red emitting materials with high QY. Herein, we report a facile and convenient hot-injection strategy to synthesize Mn-doped two-dimensional (2D) perovskite nanosheets. The emission peak can be tuned from 597 to 658 nm by manipulating the crystal field strength. In particular, a QY as high as 97% for 2D perovskite is achieved. The as-prepared perovskite also possesses excellent stability, whose emission property can be maintained for almost one year. A monochrome LED is further fabricated by employing the as-prepared perovskite as phosphor, which also shows high long-term stability. We believe that these highly efficient and stable perovskites will open up new opportunities in LED applications.

Two-dimensional (2D) bismuth oxide (Bi 2 O 3 ) heterostructured nanosheets (BOHNs) were first fabricated by a solution-based molecular self-assembly approach. The synthesized BOHNs nanosheets feature mixed α- and β-phases and rich surface/edge-active sites. When utilized as anode materials for rechargeable batteries, dual-phase BOHNs deliver an initial discharge capacity as high as 647.6 mAh g -1 and an increased capacity of over 200 mAh g -1 remained after 260 cycles for lithium-ion batteries (LIBs), and a stable cycling capacity at ∼50 mAh g -1 after 500 cycles for sodium-ion batteries (SIBs). A novel flexible 2D/1D/2D structure is further developed by implanting 2D BOHNs into conductive 1D carbon nanotubes and 2D graphene to form composite (BOHNCG) paper as free-standing anodes for both LIBs and SIBs. The capacity of 2D/1D/2D BOHNCG as a LIB anode reaches 823.5 mAh g -1 , corresponding to an enhancement of ∼27%, and remains at >110 mAh g -1 after 80 cycles as a SIB anode with greatly improved cycling stability. This work verifies the promising potential of 2D BOHNs for practical energy-related devices and enriches the current research on emerging 2D nanomaterials.

Photonic cancer hyperthermia has been considered to be one of the most representative noninvasive cancer treatments with high therapeutic efficiency and biosafety. However, it still remains a crucial challenge to develop efficient photothermal nanoagents with satisfactory photothermal performance and biocompatibility, among which two-dimensional (2D) ultrathin nanosheets have recently been regarded as the promising multifunctional theranostic agents for photothermal tumor ablation. In this work, we report, for the first time, on the construction of a novel kind of photothermal agents based on the intriguing 2D antimony(III) selenide (Sb 2 Se 3 ) nanosheets for highly efficient photoacoustic imaging-guided photonic cancer hyperthermia by near-infrared (NIR) laser activation. These Sb 2 Se 3 nanosheets were easily fabricated by a novel but efficiently combined liquid nitrogen pretreatment and freezing-thawing approach, which were featured with high photothermal-conversion capability (extinction coefficient: 33.2 L g -1 cm -1 ; photothermal-conversion efficiency: 30.78%). The further surface engineering of these Sb 2 Se 3 ultrathin nanosheets with poly(vinyl pyrrolidone) (PVP) substantially improved the biocompatibility of the nanosheets and their stability in physiological environments, guaranteeing the feasibility in photonic antitumor applications. Importantly, 2D Sb 2 Se 3 -PVP nanosheets have been certificated to efficiently eradicate the tumors by NIR-triggered photonic tumor hyperthermia. Especially, the biosafety in vitro and in vivo of these Sb 2 Se 3 ultrathin nanosheets has been evaluated and demonstrated. This work meaningfully expands the biomedical applications of 2D bionanoplatforms with a planar topology through probing into new members (Sb 2 Se 3 in this work) of 2D biomaterials with unique intrinsic physiochemical property and biological effect.

We developed a facile method for fabricating large-area, two-dimensional (2D), organic, highly crystalline films and extended it to organic thin-film transistor arrays. Tilted spinning provided oriented flow at the three-phase contact line, and a 2D crystalline film that consisted of layer-by-layer stacked 2,7-diocty[1]benzothieno[3,2- b]benzothiophene (C 8 -BTBT) was obtained facilely for organic thin-film transistors (OTFTs). The extracted field-effect mobility is 4.6 cm 2 V -1 s -1 , but with nonideal features. By applying this method to microdroplet arrays, an oriented crystal was fabricated, and the channel region for OTFTs was covered by adjusting the spinning speed. By tuning the tilt angle (θ) of the revolving substrate, we fabricated high-performance OTFT arrays with average and maximum mobilities of 7.5 and 10.1 cm 2 V -1 s -1 , respectively, which exhibited high reliability factors of over 90% and were close to that of ideal transistors. These results suggest that high-quality crystalline films can be obtained via a facile tilted-spinning method.

Anisotropic materials, especially two-dimensional (2D) layered materials formed by van der Waals force (vdW) with low-symmetry, have become a scientific hot-spot because their electrical, optical, and thermoelectric properties are highly polarization dependent. The 2D GeSe, a typical anisotropic-layered orthorhombic structure and narrow bandgap (1.1-1.2 eV) semiconductor, potentially meets these demands. In this report, the ultrathin elongated hexagonal GeSe nanoplates were successfully synthesized by the rapid physical vapor deposition method developed here. The ultrathin elongated hexagonal GeSe nanoplates have a zigzag edge in the long edge and an armchair edge in the short edge. In addition, the typical Raman mode exhibited 90° periodic vibration, having its maximum intensity between the zigzag direction or the zigzag and armchair direction, indicating an anisotropic electron-phonon interaction. Furthermore, the field effect transistor devices based on the elongated hexagonal GeSe nanoplates were constructed and exhibited the p-type semiconducting behavior with a high photoresponse characteriscs. Finally, the polarized sensitive photocurrent was identified, further revealing the intrinsically anisotropy of the GeSe nanoplate. The results illustrated here may give a useful guidance to synthesize the 2D-layered anisotropic nanomaterials and further advance the development of the polarized photodetector.

The main challenge in water electrolysis, an appealing technique to alleviate future energy crisis, is the design of efficient electrocatalysts for hydrogen evolution reaction (HER). On the basis of an interface self-assembly approach, we synthesize mesoporous nitrogen-doped carbon/Mo 2 C/reduced graphene oxide nanohybrids (denoted as mNC-Mo 2 C@rGO), which represent a new type of two-dimensional Mo 2 C/carbon hybrid nanomaterials and possess a sandwichlike structure with well-defined mesopores. The method involves the co-self-assembly of spherical micelles formed from polystyrene- block-poly(ethylene oxide), pyrrole (Py) monomers, and molybdate ions (Mo 7 O 24 6- ) on GO surfaces in aqueous solution, followed by polymerization of Py and calcination of the nanocomposites at 900 °C under nitrogen atmosphere. The resultant mNC-Mo 2 C@rGO nanosheets possess high N contents, large specific surface areas (SSAs), and 4 nm Mo 2 C particles well-distributed in the mesoporous carbon matrix. The Mo 2 C content is controllable in the range of 18.4-42.4 wt % by adjusting the feed amount of Mo 7 O 24 6- . In particular, mNC-Mo 2 C@rGO with an SSA of 344 m 2 /g and a Mo 2 C content of ca. 28 wt % exhibits the highest HER catalytic activity in 1 M KOH electrolyte, with a 95 mV overpotential at 10 mA/cm 2 , a Tafel slope of 49.8 mV/dec, and a long-term stability of 60 h at 20 mA/cm 2 . This study blazes a trail for the synthesis of new functional nanomaterials with potential applications as efficient HER electrocatalysts.

Even though a record efficiency of 23.3% has been achieved in organic-inorganic hybrid perovskite solar cells, their stability remains a critical issue, which greatly depends on the morphology of perovskite absorbers. Herein, we report a practical grain boundary modification to remarkably improve the humidity and thermal stability by gradually growing in situ two-dimensional nanoplates between the grain boundaries of perovskite films using phenylethylammonium iodide (PEAI). The experimental results show that PEAI nanoplates play a critical role in stabilizing perovskite thin films by reducing the moisture sensitivity and suppressing phase transition at the grain boundaries. In addition to the significant improved ambient stability, the grain boundary modification by PEAI can effectively suppress the nonradiative charge recombination at grain boundaries. As a result, the efficiency of perovskite solar cells is up to 20.34% with significant humidity and thermal stability.

Design of functional carbon-based nanomaterials from metal-organic frameworks (MOFs) has attracted soaring interests in recent years. However, a MOF-derived strategy toward two-dimensional (2D) nanomaterials remains a great challenge. In this work, we develop a layered Ni-hexamine framework as efficient precursor to prepare a 2D NiSe 2 /N-rich carbon nanocomposite by a simple pyrolysis and subsequent selenization process. In the 2D NiSe 2 /N-rich carbon nanocomposite, NiSe 2 nanoparticles with diameters of ca. 75 nm are homogeneously distributed in the N-rich carbon nanosheets. When serving as anode materials for sodium-ion batteries, the 2D nanocomposites exhibit a high reversible capacity of 410 mAh g -1 at 1 A g -1 and maintain a value of 255 mAh g -1 even at 10 A g -1 . The excellent electrochemical performance can be attributed to the synergistic effects between the N-rich carbon nanosheets and NiSe 2 nanoparticles. More importantly, the hexamine-based MOFs can be regarded as new and powerful platforms for the fabrication of 2D N-rich carbon-based nanomaterials, which is of great importance for various potential applications.

Two-dimensional (2D) materials have been emerging as potential candidates for the next-generation materials in various technology fields. The performance of the devices based on these 2D materials depends on their intrinsic band structures as well as the extrinsic (doping) effects such as surrounding chemicals and environmental oxygen/moisture, which strongly determines their Fermi energy level. Herein, we report the UV treatments on the 2D transition-metal dichalcogenides, to controllably dope the samples without damaging the crystal structures or quenching the luminescence properties. More surprisingly, both n-type and p-type doping can be achieved depending on the initial status of the sample and the UV treatment conditions. The doping mechanisms were elaborated on the atomic scale with transmission electron microscopy and ab initio calculations. The facile doping by UV light has potential to be integrated with photolithography processes, aiming for the large-scale integrated device/circuits design and fabrications.

Environmentally friendly tin (Sn)-based metallic halide perovskites suffer from oxidation and morphological issues. Here, we demonstrate the composition engineering of Pb-Sn-alloyed two-dimensional (2D) Ruddlesden-Popper perovskites, (BA) 2 (MA) 3 Pb 4- x Sn x I 13 , for efficient and stable solar cell applications. Smooth thin films with high surface coverage are readily formed without using any additive owing to the self-assembly characteristic of 2D perovskites. It is found that Sn plays a significant role in improving the crystallization and crystal orientation while narrowing the bandgap of Pb-Sn 2D perovskites. Photophysical studies further reveal that the optimal Sn ratio (25 mol %) based sample exhibits both minimized trap density and weakened quantum confinement for efficient charge separation. Consequently, the optimized (BA) 2 (MA) 3 Pb 3 SnI 13 -based solar cells yield the best power conversion efficiency close to 6% with suppressed hysteresis.

The most stable structures of two-dimensional Ge x P y and Ge x As y monolayers with different stoichiometries (e.g., GeP, GeP 2 , and GeP 3 ) are explored systematically through the combination of the particle-swarm optimization technique and density functional theory optimization. For GeP 3 , we show that the newly predicted most stable C2/ m structure is 0.16 eV/atom lower in energy than the state-of-the-art P3̅m1 structure reported previously ( Nano Lett. 2017, 17, 1833). The computed electronic band structures suggest that all the stable and metastable monolayers of Ge x P y are semiconductors with highly tunable band gaps under the biaxial strain, allowing strain engineering of their band gaps within nearly the whole visible-light range. More interestingly, the hole doping can convert the C2/ m GeP 3 monolayer from nonmagnetic to ferromagnetic because of its unique valence band structure. For the GeP 2 monolayer, the predicted most stable Pmc2 1 structure is a (quasi) direct-gap semiconductor that possesses a high electron mobility of ∼800 cm 2 V -1 s -1 along the k a direction, which is much higher than that of MoS 2 (∼200 cm 2 V -1 s -1 ). More importantly, the Pmc2 1 GeP 2 monolayer not only can serve as an n-type channel material in field-effect transistors but also can be an effective catalyst for splitting water.

Despite the high theoretical capacity of lithium-sulfur (Li-S) batteries, their commercialization is severely hindered by low cycle stability and low efficiency, stemming from the dissolution and diffusion of lithium polysulfides (LiPSs) in the electrolyte. In this study, we propose a novel two-dimensional conductive metal-organic framework, namely, Cu-benzenehexathial (BHT), as a promising sulfur host material for high-performance Li-S batteries. The conductivity of Cu-BHT eliminates the insulating nature of most S-based electrodes. The dissolution of LiPSs into the electrolyte is largely prevented by the strong interaction between Cu-BHT and LiPSs. In addition, orientated deposition of Li 2 S on Cu-BHT facilitates the kinetics of the LiPS redox reaction. Therefore, the use of Cu-BHT for Li-S battery cathodes is expected to suppress the LiPS shuttle effect and to improve the overall performance, which is ideal for practical application of Li-S batteries.

Novel two-dimensional (2D) Fe 2 O 3 /SnSSe hexagonal nanoplates were prepared from hot-inject process in oil phase. The resulted hybrid manifests a typical 2D hexagonal nanoplate morphology covered with thin carbon layer. Serving as anode material of lithium-ion battery (LIB), the Fe 2 O 3 /SnSSe hybrid delivers an outstanding capacity of 919 mAh g -1 at 100 mA g -1 and a discharge capacity of 293 mAh g -1 after 300 cycles at the current density of 5 A g -1 . Compared with pristine SnSSe nanoplates, the Fe 2 O 3 /SnSSe hybrid exhibits both higher capacity and better stability. The enhanced performance is mainly attributed to the 2D substrate together with the synergistic effects offered by the integration of SnSSe with Fe 2 O 3 . The 2D Fe 2 O 3 /SnSSe hybrid can afford highly accessible sites and short ion diffusion length, which facilitate the ion accessibility and improves the charge transport. The novel structure and high performance demonstrated here afford a new way for structural design and the synthesis of chalcogenides as LIB anodes.

A new crystal phase of a naphthalenediimide derivative (α-DPNDI) has been prepared via a facial polymer-assisted method. The stacking pattern of DPNDI can be tailored from the known one-dimensional (1D) ribbon (β phase) to a novel two-dimensional (2D) plate (α phase) through the assistance from polymers. We believe that the presence of polymers during crystal growth is likely to weaken the direct π-π interactions and favor side-to-side C-H-π contacts. Furthermore, β phase architecture shows electron mobility higher than that of the α phase in the single-crystal-based OFET. Theoretical calculations not only confirm that β-DPNDI has an electron transport performance better than that of the α phase but also indicate that the α phase crystal displays 2D transport while the β phase possesses 1D transport. Our results clearly suggest that polymer-assisted crystal engineering should be a promising approach to alter the electronic properties of organic semiconductors.

In this work, we report a universal surface-assisted oxidative polymerization strategy for wafer-scale fabrication of ultrathin two-dimensional conjugated microporous polymers (2D CMPs) on arbitrary substrates under ambient conditions. Three kinds of 2D CMPs with average thickness of 1.5-3.6 nm were prepared on SiO 2 /Si substrates by using carbazole based monomers. Moreover, 2D CMPs can be grown on reduced graphene oxide (rGO) substrate to construct large-area 2D CMP/rGO heterostructure. As a proof-of-concept demonstration, an organic vertical field-effect transistor based on 2D CMP/rGO heterostructures was fabricated, which exhibited typical p-type behavior with high reproducibility and on/off current ratio. Most importantly, the direct growth of large-area 2D CMPs on arbitrary substrates is compatible with the conventional processes in the semiconductor industry, and therefore is expected to expedite the development of 2D CMPs as building blocks for construction of practical electronic devices.

Hysteresis and stability issues in perovskite solar cell (PSCs) hinder their commercialization. Here, we report an effective and reproducible approach for enhancing the stability of and suppressing the hysteresis in PSCs by incorporating a small quantity of two-dimensional (2D) PEA 2 PbI 4 [PEA = C 6 H 5 (CH 2 ) 2 NH 3 ] in three-dimensional (3D) MAPbI 3 [MA = CH 3 NH 3 ] [denoted as (PEA 2 PbI 4 ) x (MAPbI 3 )], where the perovskite films were fabricated by the Lewis acid-base adduct method. A nanolaminate structure comprising layered MAPbI 3 nanobricks was created in the presence of 2D PEA 2 PbI 4 . For x = 0.017, a power conversion efficiency (PCE) of as high as 19.8% was achieved, which was comparable to the 20.0% PCE of a MAPbI 3 -based cell. Density functional theory (DFT) calculations confirmed that iodide migration was suppressed in the presence of the 2D perovskite as a result of a higher activation energy, which was responsible for the significant reduction in hysteresis and the improved chemical stability against a Ag electrode as compared to the corresponding characteristics of its pristine MAPbI 3 counterpart. An unencapsulated MAPbI 3 -based device retained less than 55% of its initial PCE in a 35-day aging test, whereas a (PEA 2 PbI 4 ) 0.017 (MAPbI 3 )-based device without encapsulation exhibited a promising long-term stability, retaining over 90% of its initial PCE after 42 days.

Herein, a two-dimensional metal-organic framework (2D MOF) made of iron porphyrin complex (TCP(Fe)) interconnected with divalent metal ion (M = Zn, Co, and Cu) is used to construct a selective layer, which is explored as an ultrafast and energy-saving nanofiltration (NF) membrane for removing organic dyes from water. Among the layered 2D M-TCP(Fe) membranes, Zn-TCP(Fe) membranes display the highest water permeance, which is 3 times higher than graphene-based membranes with similar rejection. To further improve the separation performances, we utilize polycations to anchor the periphery carboxylic groups of nanosheets, regulating the assembly of 2D Zn-TCP(Fe) nanosheets to produce a new class of crack-free selective layer possessing ultrathin and highly ordered nanochannels for efficient NF. Benefiting from these structural features, our polycation-regulated 2D Zn-TCP(Fe) membranes could offer ultrahigh permeance of 4243 L m -2 h -1 bar -1 (2-fold higher than its pristine) and excellent rejection rates (over 90%) for organic dye with size larger than 0.8 × 1.1 nm. This permeance value is about 2 orders of magnitude higher than the commercial polymeric NF membrane. Additionally, the membranes demonstrate 20-40% salt rejection.

We demonstrate the growth of thin films of molybdenum ditelluride and molybdenum diselenide on sapphire substrates by molecular beam epitaxy. In situ structural and chemical analyses reveal stoichiometric layered film growth with atomically smooth surface morphologies. Film growth along the (001) direction is confirmed by X-ray diffraction, and the crystalline nature of growth in the 2H phase is evident from Raman spectroscopy. Transmission electron microscopy is used to confirm the layered film structure and hexagonal arrangement of surface atoms. Temperature-dependent electrical measurements show an insulating behavior that agrees well with a two-dimensional variable-range hopping model, suggesting that transport in these films is dominated by localized charge-carrier states.

Few-layer two-dimensional (2D) molybdenum oxide nanoflakes are exfoliated using a grinding assisted liquid phase sonication exfoliation method. The sonication process is carried out in five different mixtures of water with both aprotic and protic solvents. We found that surface energy and solubility of mixtures play important roles in changing the thickness, lateral dimension, and synthetic yield of the nanoflakes. We demonstrate an increase in proton intercalation in 2D nanoflakes upon simulated solar light exposure. This results in substoichiometric flakes and a subsequent enhancement in free electron concentrations, producing plasmon resonances. Two plasmon resonance peaks associated with the thickness and the lateral dimension axes are observable in the samples, in which the plasmonic peak positions could be tuned by the choice of the solvent in exfoliating 2D molybdenum oxide. The extinction coefficients of the plasmonic absorption bands of 2D molybdenum oxide nanoflakes in all samples are found to be high (ε > 10(9) L mol(-1) cm(-1)). It is expected that the tunable plasmon resonances of 2D molybdenum oxide nanoflakes presented in this work can be used in future electronic, optical, and sensing devices.

Graphitic carbon nitrides have appeared as a new type of photocatalyst for water splitting, but their broader and more practical applications are oftentimes hindered by the insolubility or difficult dispersion of the material in solvents. We herein prepared novel two-dimensional (2D) carbon nitride-type polymers doped by iron under a mild one-pot method through preorganizing formamide and citric acid precursors into supramolecular structures, which eventually polycondensed into a homogeneous organocatalyst for highly efficient visible light-driven hydrogen evolution with a rate of ∼16.2 mmol g(-1) h(-1) and a quantum efficiency of 0.8%. Laser photolysis and electrochemical impedance spectroscopic measurements suggested that iron-doping enabled strong electron coupling between the metal and the carbon nitride and formed unique electronic structures favoring electron mobilization along the 2D nanomaterial plane, which might facilitate the electron transfer process in the photocatalytic system and lead to efficient H2 evolution. In combination with electrochemical measurements, the electron transfer dynamics during water reduction were depicted, and the earth-abundant Fe-based catalyst may open a sustainable strategy for conversion of sunlight into hydrogen energy and cope with current challenging energy issues worldwide.