Band structure engineering through van der Waals heterostructing superlattices of two‐dimensional transition metal dichalcogenides

Abstract

The indirect‐to‐direct band‐gap transition in transition metal dichalcogenides (TMDCs) from bulk to monolayer, accompanying with other unique properties of two‐dimensional materials, has endowed them great potential in optoelectronic devices. The easy transferability and feasible epitaxial growth pave a promising way to further tune the optical properties by constructing van der Waals heterostructures. Here, we performed a systematic high‐throughput first‐principles study of electronic structure and optical properties of the layer‐by‐layer stacking TMDCs heterostructing superlattices, with the configuration space of [(MX2)n(M′X′2)10−n] (M/M′ = Cr, Mo, W; X/X′ = S, Se, Te; n = 0‐10). Our calculations involving long‐range dispersive interaction show that the indirect‐to‐direct band‐gap transition or even semiconductor‐to‐metal transition can be realized by changing component compositions of superlattices. Further analysis indicates that the indirect‐to‐direct band‐gap transition can be ascribed to the in‐plane strain induced by lattice mismatch. The semiconductor‐to‐metal transition may be attributed to the band offset among different components that is modified by the in‐plane strain. The superlattices with direct band‐gap show quite weak band‐gap optical transition because of the spacial separation of the electronic states involved. In general, the layers stacking‐order of superlattices results in a small up to 0.2 eV band gap fluctuation because of the built‐in potential. Our results provide useful guidance for engineering band structure and optical properties in TMDCs heterostructing superlattices.

Metal Halide Semiconductors beyond Lead-Based Perovskites for Promising Optoelectronic Applications

“…In recent years, more and more attention has been focused on the exploration of emerging optoelectronic semiconductor materials, and a batch of new nontetrahedral semiconductors has emerged. For instance, two-dimensional material families represented by transition metal dichalcogenides and graphene have shown application prospects in many fields because of their unique structural features and attractive physical and chemical properties. − One-dimensional Bi/Sb-based chalcogenides, such as Sb 2 Se 3 , are used in solar cells and photodiodes because of their high light absorption, high carrier mobility, and broad spectral response, showing high power conversion efficiency and high sensitivity. , Then there is the family of materials, broadly classified as metal halide semiconductors, which includes the remarkable Pb-halide perovskites, attracting extensive attention from researchers. Different from the high-temperature synthesis of most covalent tetrahedral semiconductors, metal halide semiconductors with ionic characteristics can be prepared by low-cost solution methods .…”

Cobalt-Doping of Molybdenum Disulfide for Enhanced Catalytic Polysulfide Conversion in Lithium–Sulfur Batteries

“…For example, MoS 2 has strong interaction with LiPSs and reduces the polarization for their conversion, , and it has three polytypic structures, including metallic 1T and semiconducting 2H and 3R polymorphs. , Compared with the most stable and widely existing 2H phase, 1T MoS 2 has high conductivity, abundant active sites at the edges and on the basal plane for catalysis reactions. , However, 1T MoS 2 is unstable and tends to aggregate into a stable 2H phase because of the S–S van der Waals interaction. Several strategies have been proposed to enhance the catalytic activity of MoS 2 , , − and metal atom doping allows engineering the electronic properties and crystal structures at the same time for the catalytic performance improvement in metal–sulfur batteries. , For example, alkaline metal doping can promote the phase transition and stabilize the 1T phase with the active basal plane for hydrogen production. − Moreover, the doping element also leads to the redistribution of the density of states (DOS) and bandgap embellishment, which can further tune the catalytic activity of MoS 2 . − Therefore, regulating the doping of MoS 2 should be a promising way to further enhance their activity for LiPS conversion.…”

Electronic property modulation in two-dimensional lateral superlattices of monolayer transition metal dichalcogenides

“…Conversely, in the vertical SLs, changes in the stacking sequence will significantly affect the electronic band structure owing to the changes in the symmetry and QCE. 18,74–76 Thus, it suggests that constructing 2D lateral TMD-SLs is an excellent strategy to tune the target physical properties without changing the basic electronic band structure.…”

“…For van der Waals HSs, the selected constituent sub-lattices can be combined freely to design new materials and functionalities owing to their high in-plane stability imparted by strong covalent bonds and high assemblability benefiting from weak interlayer van der Waals interaction. 9,13–24 However, these vertical HSs have no apparent charge transfer between layers due to weak interlayer coupling, and the electronic states of the constituent sub-lattices are not significantly changed, limiting the amplitude of property modulation. Conversely, the constituent sub-lattices of 2D lateral SLs are joined via covalent bonds.…”