A van der Waals Heterostructure Based on Graphene-like Gallium Nitride and Boron Selenide: A High-Efficiency Photocatalyst for Water Splitting

Stacking engineering induced Z-scheme MoSSe/WSSe heterostructure for photocatalytic water splitting

Stacking engineering is a popular method to tune the performance of two-dimensional materials for advanced applications. In this work, Jansu MoSSe and WSSe monolayers are constructed as a van der Waals (vdWs) heterostructure by different stacking configurations. Using first-principle calculations, all the relaxed stacking configurations of the MoSSe/WSSe heterostructure present semiconductor properties while the direct type-II band structure can be obtained. Importantly, the Z-scheme charge transfer mode also can be addressed by band alignment, which shows the MoSSe/WSSe heterostructure is an efficient potential photocatalyst for water splitting. In addition, the built-in electric field of the MoSSe/WSSe vdWs heterostructure can be enhanced by the S-Se interface due to further asymmetric structures, which also results in considerable charge transfer comparing with the MoSSe/WSSe vdWs heterostructure built by the S-S interface. Furthermore, the excellent optical performances of the MoSSe/WSSe heterostructure with different stacking configurations are obtained. Our results provide a theoretical guidance for the design and control of the two-dimensional heterostructure as photocatalysts through structural stacking.

Enhancing the electronic and optical properties of the metal/semiconductor NbS2/BSe nanoheterostructure towards advanced electronics

Metal-semiconductor (M-S) contacts play a vital role in advanced applications, serving as crucial components in ultracompact devices and exerting a significant impact on overall device performance. Here, in this work, we design a M-S nanoheterostructure between a metallic NbS2 monolayer and a semiconducting BSe monolayer using first-principles prediction. The stability of such an M-S nanoheterostructure is verified and its electronic and optical properties are also considered. Our results indicate that the NbS2/BSe nanoheterostructure is structurally, mechanically and thermally stable. The formation of the NbS2/BSe heterostructure leads to the generation of a Schottky contact with the Schottky barrier ranging from 0.36 to 0.51 eV, depending on the stacking configurations. In addition, the optical absorption coefficient of the NbS2/BSe heterostructure can reach up to 5 × 105 cm-1 at a photon energy of about 5 eV, which is still greater than that in the constituent NbS2 and BSe monolayers. This finding suggests that the formation of the M-S NbS2/BSe heterostructure gives rise to an enhancement in the optical absorption of both NbS2 and BSe monolayers. Notably, the tunneling probability and the contact tunneling-specific resistivity at the interface of the NbS2/BSe heterostructure are low, indicating its applicability in emerging nanoelectronic devices, such as Schottky diodes and field-effect transistors. Our findings offer valuable insights for the practical utilization of electronic devices based on the NbS2/BSe heterostructure.

Tunable Electronic Properties, Carrier Mobility, and Contact Characteristics in Type-II BSe/Sc2CF2 Heterostructures toward Next-Generation Optoelectronic Devices

Conducting heterostructures have emerged as a promising strategy to enhance physical properties and unlock the potential application of such materials. Herein, we conduct and investigate the electronic and transport properties of the BSe/Sc2CF2 heterostructure using first-principles calculations. The BSe/Sc2CF2 heterostructure is structurally and thermodynamically stable, indicating that it can be feasible for further experiments. The BSe/Sc2CF2 heterostructure exhibits a semiconducting behavior with an indirect band gap and possesses type-II band alignment. This unique alignment promotes efficient charge separation, making it highly promising for device applications, including solar cells and photodetectors. Furthermore, type-II band alignment in the BSe/Sc2CF2 heterostructure leads to a reduced band gap compared to the individual BSe and Sc2CF2 monolayers, leading to enhanced charge carrier mobility and light absorption. Additionally, the generation of the BSe/Sc2CF2 heterostructure enhances the transport properties of the BSe and Sc2CF2 monolayers. The electric fields and strains can modify the electronic properties, thus expanding the potential application possibilities. Both the electric fields and strains can tune the band gap and lead to the type-II to type-I conversion in the BSe/Sc2CF2 heterostructure. These findings shed light on the versatile nature of the BSe/Sc2CF2 heterostructure and its potential for advanced nanoelectronic and optoelectronic devices.

Ultrahigh Carrier Mobility in Two-Dimensional IV-VI Semiconductors for Photocatalytic Water Splitting

Two-dimensional materials have been developed as novel photovoltaic and photocatalytic devices because of their excellent properties. In this work, four δ-IV-VI monolayers, GeS, GeSe, SiS and SiSe, are investigated as semiconductors with desirable bandgaps using the first-principles method. These δ-IV-VI monolayers exhibit exceptional toughness; in particular, the yield strength of the GeSe monolayer has no obvious deterioration at 30% strain. Interestingly, the GeSe monolayer also possesses ultrahigh electron mobility along the x direction of approximately 32,507 cm²·V^-1·s^-1, which is much higher than that of the other δ-IV-VI monolayers. Moreover, the calculated capacity for hydrogen evolution reaction of these δ-IV-VI monolayers further implies their potential for applications in photovoltaic and nano-devices.

Understanding Electronic Properties and Tunable Schottky Barriers in a Graphene/Boron Selenide van der Waals Heterostructure

van der Waals heterostructures provide a powerful platform for engineering the electronic properties and for exploring exotic physical phenomena of two-dimensional materials. Here, we construct a graphene/BSe heterostructure and examine its electronic characteristics and the tunability of contact types under electric fields. Our results reveal that the graphene/BSe heterostructure is energetically, mechanically, and thermodynamically stable at room temperature. It forms a p-type Schottky contact and exhibits a high carrier mobility, making it a promising candidate for future Schottky field-effect transistors. Furthermore, applying an electric field not only reduces contact barriers but also induces a transition from a p-type to an n-type Schottky contact and from a Schottky to an ohmic contact, offering further potential for the control and manipulation of the heterostructure's electronic properties. Our findings offer a rational basis for the design of energy-efficient and tunable heterostructure devices based on the graphene/BSe heterostructure.

A semiconductor Sc2S3 monolayer with ultrahigh carrier mobility for UV blocking filter application

For humans, ultraviolet (UV) light from sun is harmful to our eyes and eye-related cells. This detrimental fact requires scientists to search for a material that can efficiently absorb UV light while allowing lossless transmission of visible light. Using an unbiased first-principles swarm intelligence structure search, we explored two-dimensional (2D) Sc-S crystals and identified a novel Sc₂S₃ monolayer with good thermal and dynamical stability. The optoelectronic property simulations revealed that the Sc₂S₃ monolayer has a wide indirect bandgap (3.05 eV) and possesses an ultrahigh carrier mobility (2.8 × 10³ cm² V^-1 s^-1). Remarkably, it has almost transparent visible light absorption, while it exhibits an ultrahigh absorption coefficient up to × 10⁵ cm^-1 in the ultraviolet region. Via the application of biaxial strain and thickness modulation, the UV light absorption coefficients of Sc₂S₃ can be further improved. These findings manifest an attractive UV blocking optoelectronic characteristic of the Sc₂S₃ configuration as a prototypical nanomaterial for the potential application in UV blocking filters.

Excellent photocatalytic properties in 2D ZnO/SiC van der Waals hetero-bilayers: water-splitting H2-fuel production

This research unravels the photocatalytic properties of a 2D ZnO/SiC van der Waals hetero-bilayer for potential water-splitting applications by first-principles calculations. Four unique stacking patterns are considered in studying the electronic and optical properties in the presence and absence of biaxial external strain. For pattern-I and II, large negative binding energy and positive phonon frequencies are observed, denoting chemical and mechanical stabilities. Under the HSE-06 pseudo potential, the calculated bandgap value for pattern-I and II reaches 2.86 eV and 2.74 eV, respectively. 2D ZnO/SiC shows a high absorption coefficient (∼10⁵ cm^-1). The absorption peak under biaxial strain could reach ∼3.5 times the peak observed under unstrained conditions. Under strain, a shift from compressive to tensile biaxial strain (-6% to 6%) results in a bandgap decrease from 3.18 eV to 2.52 eV and 3.09 eV to 2.43 eV, for pattern-I and II, respectively. The observed strain-driven kinetic overpotential for 2D ZnO/SiC pattern-I and II easily engenders photocatalytic redox reactions. The excellent mechanical durability and strain-driven large kinetic overpotential suggest 2D ZnO/SiC heterobilayers as a prospective material for water-splitting H₂-fuel production.

First-principles investigation of potential water-splitting photocatalysts and photovoltaic materials based on Janus transition-metal dichalcogenide/WSe2 heterostructures

Two-dimensional materials have been shown to exhibit exotic properties that make them very interesting for both photo-catalytic and photo-voltaic applications. In this study, van der Waals corrected density functional theory calculations were carried out on heterostructures of MoSSe/WSe2, WSSe/WSe2, and WSeTe/WSe2. The heterostructures are semiconductors with type II band alignments which are advantageous for electron-hole pair separation. The HSE06 level electronic band gap was found to be 1.093 eV, 1.427 eV and 1.603 eV for MoSSe/WSe2, WSSe/WSe2, and WSeTe/WSe2 respectively. We have considered eight high symmetry stacking patterns for each of the heterostructures, and among them the most stable stacking orders were ascertained based on the interlayer binding energies. The binding energies of the most stable MoSSe/WSe2, WSSe/WSe2, and WSeTe/WSe2 heterostructures were found to be -0.0604 eV, -0.1721 eV, and -0.3296 eV with an equilibrium interlayer space of 5.75 Å, 4.05 Å, and 4.76 Å respectively. The Power Conversion Efficiency (PCE) was found to be 20, 19.98, and 18.24 percent for the MoSSe/WSe2, WSSe/WSe2, and WSeTe/WSe2 heterostructures, respectively. The results show that they can serve as suitable photovoltaic materials with high efficiency, thus, opening the possibilities of developing solar cells based on 2D Janus/TMD heterostructures. The most stable heterostructures are also tested for photocatalytic water splitting applications and WSeTe/WSe2 shows excellent photocatalytic activity by being active for full water splitting at pH = 7 and pH = 14, the MoSSe/WSe2 heterostructure is good for the oxygen evolution reaction and WSSe/WSe2 is active for the hydrogen evolution reaction.

Zinc iron selenide nanoflowers anchored g-C3N4 as advanced catalyst for photocatalytic water splitting and dye degradation

Hydrogen has been considered as a promising clean energy source owing to its renewability and zero carbon emission. Accordingly, photocatalytic water splitting has drawn much attention as a key green technology of producing hydrogen. However, it has remained as a great challenge due to the low production rate and expensive constituents of photocatalytic systems. Herein, we synthesised nanostructures consisting of transition metal selenide and g-C₃N₄ for photocatalytic water splitting reaction. They include ZnSe, FeSe₂, Zn/FeSe₂ and ZnFeSe₂ nanoflowers and a nanocomposite made of Zn/FeSe₂ and g-C₃N₄. Hydrogen evolution rates in the presence of ZnSe, FeSe₂, Zn/FeSe₂ and ZnFeSe₂ photocatalysts were measured as 60.03, 128.02, 155.11 and 83.59 μmolg^-1 min^-1, respectively. On the other hand, with the nanocomposite consisting of Zn/FeSe₂ and g-C₃N₄, the hydrogen and oxygen evolution rates were significantly enhanced up to 202.94 μmol g^-1min^-1 and 90.92 μmol g^-1min^-1, respectively. The nanocomposite was also examined as a photocatalyst for degradation of rhodamine B showing that it photodegrades the compound two times faster compared to pristine Zn/FeSe₂ nanoflowers without g-C₃N_4. Our study suggests the nanocomposite of Zn/FeSe₂ and g-C₃N₄ as a promising photocatalyst for energy and environmental applications.

The SWSe-BP vdW Heterostructure as a Promising Photocatalyst for Water Splitting with Power Conversion Efficiency of 19.4

Hydrogen generation by photocatalytic water splitting has drawn enormous research attention for converting sunlight and water into clean and green hydrogen fuel. However, the search for a high efficiency photocatalyst for water splitting is a key challenge. Two dimensional (2D) van der Waals (vdW) heterostructures as photocatalysts exhibit many advantages over the stacked original materials. In this article, we designed two novel 2D vdW heterostructures composed of WSSe and blue phosphorene (BP) monolayers, SWSe-BP and SeWS-BP, which are thermodynamically stable at room temperature. Using first-principles calculations, we found that the SWSe-BP vdW heterostructure can act as a potential photocatalyst for water splitting due to its robust stabilities, type-II band alignment, moderate bandgap, and suitable band edge positions for the redox reactions of water splitting, strong optical absorption, and excellent power conversion efficiency (PCE). Remarkably, the PCE of the SWSe-BP vdW heterostructure can achieve approximately 19.4% under a 3% biaxial tensile strain.

The First-Principles Study of External Strain Tuning the Electronic and Optical Properties of the 2D MoTe2/PtS2 van der Waals Heterostructure

Two-dimensional van der Waals (vdW) heterostructures reveal novel properties due to their unique interface, which have attracted extensive focus. In this work, the first-principles methods are explored to investigate the electronic and the optical abilities of the heterostructure constructed by monolayered MoTe₂ and PtS₂. Then, the external biaxial strain is employed on the MoTe₂/PtS₂ heterostructure, which can persist in the intrinsic type-II band structure and decrease the bandgap. In particular, the MoTe₂/PtS₂ vdW heterostructure exhibits a suitable band edge energy for the redox reaction for water splitting at pH 0, while it is also desirable for that at pH 7 under decent compressive stress. More importantly, the MoTe₂/PtS₂ vdW heterostructure shows a classy solar-to-hydrogen efficiency, and the light absorption properties can further be enhanced by the strain. Our results showed an effective theoretical strategy to tune the electronic and optical performances of the 2D heterostructure, which can be used in energy conversion such as the automotive battery system.

First-Principles Calculations of Two-Dimensional CdO/HfS2 Van der Waals Heterostructure: Direct Z-Scheme Photocatalytic Water Splitting

Using two-dimensional (2D) heterostructure as photocatalyst for water splitting is a popular strategy for the generation of hydrogen. In this investigation, the first-principles calculations are explored to address the electronic performances of the 2D CdO/HfS₂ heterostructure formed by van der Waals (vdW) forces. The CdO/HfS₂ vdW heterostructure has a 1.19 eV indirect bandgap with type-II band alignment. Importantly, the CdO/HfS₂ vdW heterostructure possesses an intrinsic Z-scheme photocatalytic characteristic for water splitting by obtaining decent band edge positions. CdO donates 0.017 electrons to the HfS₂ layer in the heterostructure, inducing a potential drop to further separate the photogenerated electrons and holes across the interface. The CdO/HfS₂ vdW heterostructure also has excellent optical absorption capacity, showing a promising role as a photocatalyst to decompose the water.

Stacking-Mediated Type-I/Type-II Transition in Two-Dimensional MoTe2/PtS2 Heterostructure: A First-Principles Simulation

Recently, a two-dimensional (2D) heterostructure has been widely investigated as a photocatalyst to decompose water using the extraordinary type-II band structure. In this work, the MoTe2/PtS2 van der Waals heterostructure (vdWH) is constructed with different stacking structures. Based on density functional calculations, the stacking-dependent electronic characteristic is explored, so that the MoTe2/PtS2 vdWH possesses type-I and type-II band structures for the light-emitting device and photocatalyst, respectively, with decent stacking configurations. The band alignment of the MoTe2/PtS2 vdWH is also addressed to obtain suitable band edge positions for water-splitting at pH 0. Furthermore, the potential drop is investigated, resulting from charge transfer between the MoTe2 and PtS2, which is another critical promotion to prevent the recombination of the photogenerated charges. Additionally, the MoTe2/PtS2 vdWH also demonstrates a novel and excellent optical absorption capacity in the visible wavelength range. Our work suggests a theoretical guide to designing and tuning the 2D heterostructure using photocatalytic and photovoltaic devices.

Boosting the photocatalytic H2 evolution activity of type-II g-GaN/Sc2CO2 van der Waals heterostructure using applied biaxial strain and external electric field

Two-dimensional (2D) van der Waals (vdW) heterostructures are a new class of materials with highly tunable bandgap transition type, bandgap energy and band alignment. Herein, we have designed a novel 2D g-GaN/Sc2CO2 heterostructure as a potential solar-driven photocatalyst for the water splitting process and investigate its catalytic stability, interfacial interactions, and optical and electronic properties, as well as the effects of applying an electric field and biaxial strain using first-principles calculation. The calculated lattice mismatch and binding energy showed that g-GaN and Sc2CO2 are in contact and may form a stable vdW heterostructure. Ab initio molecular dynamics and phonon dispersion simulations show thermal and dynamic stability. g-GaN/Sc2CO2 has an indirect bandgap energy with appropriate type-II band alignment relative to the water redox potentials. Meanwhile, the interfacial charge transfer from g-GaN to Sc2CO2 can effectively separate electron-hole pairs. Moreover, a potential drop of 3.78 eV is observed across the interface, inducing a built-in electric field pointing from g-GaN to Sc2CO2. The heterostructure shows improved visible-light optical absorption compared to the isolated g-GaN and Sc2CO2 monolayers. Our study demonstrates that tunable electronic and structural properties can be realised in the g-GaN/Sc2CO2 heterostructure by varying the electric field and biaxial strain. In particular, the compressive strain and negative electric field are more effective for promoting hydrogen production performance. Since it is challenging to tune the electric field and biaxial strain experimentally, our research provides strategies to boost the performance of MXene-based heterojunction photocatalysts in solar harvesting and optoelectronic devices.

Recent progress of heterostructures based on two dimensional materials and wide bandgap semiconductors

Recent progress in the synthesis and assembly of two-dimensional (2D) materials has laid the foundation for various applications of atomically thin layer films. These 2D materials possess rich and diverse properties such as layer-dependent band gaps, interesting spin degrees of freedom, and variable crystal structures. They exhibit broad application prospects in micro-nano devices. In the meantime, the wide bandgap semiconductors (WBS) with an elevated breakdown voltage, high mobility, and high thermal conductivity have shown important applications in high-frequency microwave devices, high-temperature and high-power electronic devices. Beyond the study on single 2D materials or WBS materials, the multi-functional 2D/WBS heterostructures can promote the carrier transport at the interface, potentially providing novel physical phenomena and applications, and improving the performance of electronic and optoelectronic devices. In this review, we overview the advantages of the heterostructures of 2D materials and WBS materials, and introduce the construction methods of 2D/WBS heterostructures. Then, we present the diversity and recent progress in the applications of 2D/WBS heterostructures, including photodetectors, photocatalysis, sensors, and energy related devices. Finally, we put forward the current challenges of 2D/WBS heterostructures and propose the promising research directions in the future.

Aligned Stacking of Nanopatterned 2D Materials for High-Resolution 3D Device Fabrication

Two-dimensional materials can be combined by placing individual layers on top of each other, so that they are bound only by their van der Waals interaction. The sequence of layers can be chosen arbitrarily, enabling an essentially atomic-level control of the material and thereby a wide choice of properties along one dimension. However, simultaneous control over the structure in the in-plane directions is so far still rather limited. Here, we combine spatially controlled modifications of 2D materials, using focused electron irradiation or electron beam induced etching, with the layer-by-layer assembly of van der Waals heterostructures. The presented assembly process makes it possible to structure each layer with an arbitrary pattern prior to the assembly into the heterostructure. Moreover, it enables a stacking of the layers with accurate lateral alignment, with an accuracy of currently 10 nm, under observation in an electron microscope. Together, this enables the fabrication of almost arbitrary 3D structures with highest spatial resolution.

Ab Initio Calculations for the Electronic, Interfacial and Optical Properties of Two-Dimensional AlN/Zr2CO2 Heterostructure

Recently, expanding the applications of two-dimensional (2D) materials by constructing van der Waals (vdW) heterostructures has become very popular. In this work, the structural, electronic and optical absorption performances of the heterostructure based on AlN and Zr2CO2 monolayers are studied by first-principles simulation. It is found that AlN/Zr2CO2 heterostructure is a semiconductor with a band gap of 1.790 eV. In the meanwhile, a type-I band structure is constructed in AlN/Zr2CO2 heterostructure, which can provide a potential application of light emitting devices. The electron transfer between AlN and Zr2CO2 monolayer is calculated as 0.1603 |e| in the heterostructure, and the potential of AlN/Zr2CO2 heterostructure decreased by 0.663 eV from AlN layer to Zr2CO2 layer. Beisdes, the AlN/Zr2CO2 vdW heterostructure possesses excellent light absorption ability of in visible light region. Our research provides a theoretical guidance for the designing of advanced functional heterostructures.

Mechanical, electronic and optical properties of a novel B2P6 monolayer: ultrahigh carrier mobility and strong optical absorption

Two-dimensional (2D) materials with a moderate bandgap and high carrier mobility are useful for applications in optoelectronics. In this work, we present a systematic investigation of the mechanical, electronic and optical properties of a B₂P₆ monolayer using first-principles calculations. Monolayer B₂P₆ was estimated to be an anisotropic material from direction-dependent in-plane Young's moduli and Poisson's ratios. Also, B₂P₆ exhibits an ultrahigh electron mobility of ∼5888 cm² V^-1 s^-1, showing advantages for application in high-speed optoelectronic devices. More importantly, for the B₂P₆ monolayer, a desirable transformation from an indirect to direct band gap was observed at a biaxial tensile strain of ∼4%. Increasing the biaxial strain reduces the gap and preserves the suitable band edge positions for photocatalytic water splitting in the observed strain range of 1-8%. The decreased gap also enhances the visible light absorption of the B₂P₆ monolayer. These findings indicate that the B₂P₆ monolayer has promising applications in photocatalytic and photovoltaic devices.

Superior tunable photocatalytic properties for water splitting in two dimensional GeC/SiC van der Waals heterobilayers

The photocatalytic characteristics of two-dimensional (2D) GeC-based van der Waals heterobilayers (vdW-HBL) are systematically investigated to determine the amount of hydrogen (H2) fuel generated by water splitting. We propose several vdW-HBL structures consisting of 2D-GeC and 2D-SiC with exceptional and tunable optoelectronic properties. The structures exhibit a negative interlayer binding energy and non-negative phonon frequencies, showing that the structures are dynamically stable. The electronic properties of the HBLs depend on the stacking configuration, where the HBLs exhibit direct bandgap values of 1.978 eV, 2.278 eV, and 2.686 eV. The measured absorption coefficients for the HBLs are over ~ 105 cm-1, surpassing the prevalent conversion efficiency of optoelectronic materials. In the absence of external strain, the absorption coefficient for the HBLs reaches around 1 × 106 cm-1. With applied strain, absorption peaks are increased to ~ 3.5 times greater in value than the unstrained HBLs. Furthermore, the HBLs exhibit dynamically controllable bandgaps via the application of biaxial strain. A decrease in the bandgap occurs for both the HBLs when applied biaxial strain changes from the compressive to tensile strain. For + 4% tensile strain, the structure I become unsuitable for photocatalytic water splitting. However, in the biaxial strain range of - 6% to + 6%, both structure II and structure III have a sufficiently higher kinetic potential for demonstrating photocatalytic water-splitting activity in the region of UV to the visible in the light spectrum. These promising properties obtained for the GeC/SiC vdW heterobilayers suggest an application of the structures could boost H2 fuel production via water splitting.

Electronic and optical properties of two-dimensional heterostructures based on Janus XSSe (X = Mo, W) and Mg(OH)2: a first principles investigation

Two-dimensional (2D) materials have attracted numerous investigations after the discovery of graphene. 2D van der Waals (vdW) heterostructures are a new generation of layered materials, which can provide more desirable applications. In this study, the first principles calculation was implemented to study the heterostructures based on Janus TMDs (MoSSe and WSSe) and Mg(OH)₂ monolayers, which were constructed by vdW interactions. Both MoSSe/Mg(OH)₂ and WSSe/Mg(OH)₂ vdW heterostructures have thermal and dynamic stability. Besides, XSSe/Mg(OH)₂ (X = Mo, W) possesses a direct bandgap with a type-I band alignment, which provides promising applications for light-emitting devices. The charge density difference was investigated, and 0.003 (or 0.0042) |e| were transferred from MoSSe (or WSSe) layer to Mg(OH)₂ layer, and the potential drops were calculated to be 11.59 and 11.44 eV across the interface of the MoSSe/Mg(OH)₂ and WSSe/Mg(OH)₂ vdW heterostructures, respectively. Furthermore, the MoSSe/Mg(OH)₂ and WSSe/Mg(OH)₂ vdW heterostructures have excellent optical absorption wave. Our studies exhibit an effective method to construct new heterostructures based on Janus TMDs and develop their applications for future light emitting devices.

Two-dimensional (2D) materials have attracted numerous investigations after the discovery of graphene.

First-Principles Study of Electronic and Optical Properties of Two-Dimensional WSSe/BSe van der Waals Heterostructure with High Solar-to-Hydrogen Efficiency

In this paper, the optical and electronic properties of WSSe/BSe heterostructure are investigated by first-principles calculations. The most stable stacking pattern of the WSSe/BSe compounds is formed by van der Waals interaction with a thermal stability proved by ab initio molecular dynamics simulation. The WSSe/BSe heterostructure exhibits a type-I band alignment with direct bandgap of 2.151 eV, which can improve the effective recombination of photoexcited holes and electrons. Furthermore, the band alignment of the WSSe/BSe heterostructure can straddle the water redox potential at pH 0–8, and it has a wide absorption range for visible light. In particular, the solar-to-hydrogen efficiency of the WSSe/BSe heterostructure is obtained at as high as 44.9% at pH 4 and 5. All these investigations show that the WSSe/BSe heterostructure has potential application in photocatalysts to decompose water.

Theoretical perspective on the electronic structure and optoelectronic properties of type-II SiC/CrS2van der Waals heterostructure with high carrier mobilities

Two-dimensional heterostructures formed by stacking layered materials play a significant role in condensed matter physics and materials science due to their potential applications in high-efficiency nanoelectronic and optoelectronic devices. In this paper, the structural, electronic, and optical properties of SiC/CrS₂van der Waals heterostructure (vdWHs) have been investigated by means of density functional theory calculations. It is confirmed that the SiC/CrS₂vdWHs is energetically and thermodynamically stable indicating its great promise for experimental realization. We find that the SiC/CrS₂vdWHs has a direct-band gap and type-II (staggered) band alignment, which can effectively separate the photo-induced electrons and holes pairs and extend their life time. The carrier mobilities of electrons and holes along the armchair and zigzag directions are as high as 6.621 × 10³and 6.182 × 10⁴ cm² V^-1 s^-1, respectively. Besides, the charge difference and potential drop across the interface can induce a large built-in electric field across the heterojunction, which will further hinder the electron and hole recombination. The SiC/CrS₂vdWHs has enhanced optical absorption capability compared to individual monolayers. This study demonstrates that the SiC/CrS₂vdWHs is a good candidate for application in the nanoelectronic and optoelectronic devices.

Type-I band alignment of BX-ZnO (X = As, P) van der Waals heterostructures as high-efficiency water splitting photocatalysts: a first-principles study

In this work, we perform first-principles calculations to examine the electronic, optical and photocatalytic properties of the BX–ZnO (X = As, P) heterostructures. The interlayer distance and binding energy of the most energetically favorable stacking configuration are 3.31 Å and −0.30 eV for the BAs–ZnO heterostructure and 3.30 Å and −0.25 eV for the BP–ZnO heterostructure. All the stacking patterns of the BX–ZnO heterostructures are proved to have thermal stability by performing AIMD simulations. The BAs–ZnO and BP–ZnO heterostructures are semiconductors with direct band gaps of 1.43 eV and 2.35 eV, respectively, and they exhibit type-I band alignment, which make them suitable for light emission applications with the ultra-fast recombination between electrons and holes. Both the BAs–ZnO and BP–ZnO heterostructures can exhibit a wider optical absorption range for visible-light owing to their reduced band gaps compared with the isolated BAs, BP and ZnO monolayers. The band alignment of both the BAs–ZnO and BP–ZnO heterostructures can straddle the water redox potential and they would have better performances owing to the direct band gap and the reduced band gap. All these findings demonstrate that the BX–ZnO heterostructures can be considered as potential photocatalysts for water splitting.

In this work, we perform first-principles calculations to examine the electronic, optical and photocatalytic properties of the BX–ZnO (X = As, P) heterostructures.

A direct Z-scheme PtS2/arsenene van der Waals heterostructure with high photocatalytic water splitting efficiency

To overcome current serious energy and environmental issues, photocatalytic water splitting holds great promise because it requires only solar energy as an energy input to produce hydrogen. In this work, based on first-principle calculations, we studied the van der Waals heterostructure formed by PtS₂ and arsenene (Are) monolayers that were successfully synthesized on a large scale at high quality. From an analysis of the migration paths of photoinduced electrons and holes, a direct Z-scheme photocatalytic mechanism is demonstrated in this heterostructure. Furthermore, the PtS₂/Are direct Z-scheme heterostructure has decent band edge positions to promote the redox reaction to decompose water at pH 0. The interfacial charge difference and potential drop are presented, which further support the formation of a direct Z-scheme photocatalyst. More importantly, the PtS₂/Are heterostructure has quite high solar-to-hydrogen (STH) efficiency (49.32%), significantly enhanced compared with isolated PtS₂ (12.67%) or Are (10.34%) monolayers. This direct Z-scheme PtS₂/Are heterostructure with excellent STH efficiency suggests its promising application as a photocatalyst for water splitting.

Design of MoS2/Graphene van der Waals Heterostructure as Highly Efficient and Stable Electrocatalyst for Hydrogen Evolution in Acidic and Alkaline Media

The thermodynamically stable phase of molybdenum disulfide (MoS₂) is evaluated as a promising and durable nonprecious-metal electrocatalyst toward the hydrogen evolution reaction (HER); however, its actual catalytic activity is restricted by an inert basal plane, low electronic conductivity, low density, and using efficiency of edged atoms. Moreover, 2D/2D van der Waals (vdws) heterostructures (HSs) with face-to-face contact can construct a highly coupled interface and are demonstrated to have immense potential for catalytic applications. In the present work, a 2D/2D hetero-layered architecture of an electrocatalyst, based on the alternate arrangement of ultrasmall monolayer MoS₂ nanosheets (approximately 5-10 nm) and ultrathin graphene (G) sheets, is prepared by a facilely chemical process, which is named as MoS₂/G HS. The unique structural characteristic of MoS₂/G HS is in favor of accommodating more active sites as the centers of ad/desorption hydrogen and transferring and separating the charges at a coupled interface to improve the electronic conductivity and durability. The density functional theory calculation results further confirm that the alternately arranged G layers and MoS₂ monolayers, as well as the expanded interplanar distance of 1.104 nm for MoS₂/G HS, can exhibit a superior HER performance in both 0.5 M H₂SO₄ and 1.0 M KOH.

Electronic structures, and optical and photocatalytic properties of the BP–BSe van der Waals heterostructures

The combination of two-dimensional materials in the form of van der Waals (vdW) heterostructures has been shown to be an effective method for designing electronic and optoelectronic equipment.

Electronic and photocatalytic properties of two-dimensional boron phosphide/SiC van der Waals heterostructure with direct type-II band alignment: a first principles study

Designing van der Waals (vdW) heterostructures of two-dimensional materials is an efficient way to realize amazing properties as well as opening opportunities for applications in solar energy conversion and nanoelectronic and optoelectronic devices. In this work, we investigate the electronic, optical, and photocatalytic properties of a boron phosphide–SiC (BP–SiC) vdW heterostructure using first-principles calculations. The relaxed configuration is obtained from the binding energies, inter-layer distance, and thermal stability. We show that the BP–SiC vdW heterostructure has a direct band gap with type-II band alignment, which separates the free electrons and holes at the interface. Furthermore, the calculated absorption spectra demonstrate that the optical properties of the BP–SiC heterostructure are enhanced compared with those of the constituent monolayers. The intensity of optical absorption can reach up to about 10⁵ cm⁻¹. The band edges of the BP–SiC heterostructure are located at energetically favourable positions, indicating that the BP–SiC heterostructure is able to split water under working conditions of pH = 0–3. Our theoretical results provide not only a fascinating insight into the essential properties of the BP–SiC vdW heterostructure, but also helpful information for the experimental design of new vdW heterostructures.

We investigate the structural, electronic, optical and photocatalytic properties of boron phosphide and SiC monolayers and their corresponding van der Waals heterostructure by density functional theory.