First-principles Calculations On The Structure And Properties Of GeP₃/Transition Metal Dichalcogenides Heterostructures

In recent years,the portable and wearable electronic devices are increasingly demanded in market,thus the flexible lithium batteries,especially the flexible electrode materials are urgently requested.Transition metal dichalcogenides(TMDs),as well as GeP₃,have similar lamellar structural features as graphene,on the other hand,their mechanical,optical,electrochemical,thermal,and electronic properties are comparable or even better than graphene.Constructing novel heterostructures with excellent properties based on TMDs and some other layer compounds has been an emerging research topic in recent years.In this work,the novel heterostructures based on TMDs with formula MX₂(M=Mo,W,Nb;X=S,Se,Te)and GeP₃ were constructed the crystal structures,electronic structures,optical properties,mechanical properties and lithium adsorption behavior of GeP₃/MX₂ heterostructures were systematically studied using first-principles calculations based on density functional theory,in order to explore its potential applications in optical devices and anode material for flexible lithium batteries.The main work and results are presented in the following:It is found that with the decrease of layer number,the TMDs(WSe₂,MoSe₂,WTe₂ and MoTe₂)change from the indirect band gap semiconductor of the bulk to the direct band gap semiconductor of monolayer,and the band gap increases gradually.Meanwhile,the band gap shifts from the infrared region towards the near-infrared or visible regions,indicating this kind of TMDs materials have potential applications for optoelectronic devices.For Nb S₂ and Nb Se₂ monolayers,the Fermi levels passe through an energy band,thus exhibit metallic nature.The two-dimensional(2D)GeP₃is an indirect band gap semiconductor.The GeP₃ has good lattice matching with the2D TMDs and the formation energy is negative,indicating that it is feasible to construct a stable GeP₃/MX₂ heterostructure.As for the band structure of the GeP₃/MoTe₂ heterostructures,one of conduction band level across the Fermi level,revealing its metallic nature.The GeP₃/WSe₂,GeP₃/MoSe₂ and GeP₃/WTe₂ heterostructures are indirect bandgap semiconductors,improve optical performance in the ultraviolet and visible regions compared with their single counterpart,implying that the heterostructures can break through the limitation of 2D materials and broaden their application in the field of optoelectronic devices.The metallic nature of GeP₃/Nb X₂(X=S,Se)heterostructures present extra new electronicstates,which directly participate in the material conductance process by reducing the energy barriar when transfering from the valence band to the bottom of the conduction band,so the electrical conductivity is greatly improved compared with the single part Nb X₂.The charges redistribute significantly in GeP₃/Nb X₂heterostructures.In the adjacent of the two layers,besides the van der Waals interactions,some weak ionic interactions also exist.Both the monolayers of GeP₃ and Nb X₂,as well as the GeP₃/Nb X₂heterostructures are isotropic.Compared with other isotropic two-dimensional materials,such as graphene and BN,GeP₃/Nb X₂heterostructures have superior flexibility due to their smaller Young's moduli.The lithium storage capacity of GeP₃/Nb S₂ heterostructure is 447.047 m Ah/g,which is higher than the anode materials of graphite(372 m Ah/g).In summary,the GeP₃/Nb X₂heterostructures have good structural stability,electrical conductivity and omnidirectional flexibility,which is an ideal material for portable lithium-ion battery flexible electrodes potentially.