First-principles Study Of Optical Properties Of The MoS₂ And MoSe₂ Monolayers With B,C,N Dopants And Li Adatoms

Two-dimensional transition metal dichalcogenides?TMD?which could be represented by MoS₂ are new layered materials after graphene.Especially,their monolayers exhibit novel electronic,and optical properties and hence receive a huge concern in fields of low power electronic products,photoelectric devices,solar cells,and energy collecting materials.In order to investigate the physical and chemical mechanism behind these excellent properties,and enhance monolayer material's light response range of the sunlight energy,and tune their light absorption to the light wavelength that we hoped,we studied the optical properties of monolayer MoS₂,MoSe₂,WS₂ by means of doping and absorbing appropriate atoms,using first principle calculations based on the density functional theory.The work provides theoretical reference for the design and preparation of efficient photoelectric materials.Firstly,the electronic and optical properties of the WS₂ monolayer are explored based on the density functional theory.The present results show that WS₂ monolayer demonstrates large absorption coefficient and photoconductivity,high refraction index in the visible light range.Generally,the optical properties of the WS₂ monolayer are very similar to those of MoS₂ the optical properties,although about 0.2 eV ultraviolet-shift has been found in the visible light range.It is implied the WS₂ monolayer can also be widely used as an efficient optical material as a MoS₂ monolayer.The mechanism of the optical properties is explored with the density of state and partial density of state.Secondly,investigations were performed on the effect of different B-,C-,and N-doped concentrations and positions on the electronic and optical properties of the MoS₂ monolayer,based on the same calculation principle.The results show that the absorption coefficient in the near-infrared region?NIR?and most visible region were enhanced by the three different atoms,respectively.Moreover,the absorption coefficient increased continuously with increasing concentrations of each kind of atoms,implying that the B-,C-doped MoS₂ monolayer could be used to design the materials for the solar light energy collection or light catalysis.Simultaneously,take C-doped MoS₂ as anexample,the change mechanism of the optical properties were illustrated from the perspective of the electronic structure.Finally,the Li-adsorbed effects on the optical properties of MoS₂ and MoSe₂ monolayers have been explored using the first principle calculations.Eight kinds of Li adsorption concentrations are considered.The absorption coefficients are calculated using the fully optimized geometrical structures.The effect mechanism of the Li atoms on the optical properties is explored with the density of state and partial density of state.The energy stability of the high adsorption concentrations is examined with molecular dynamics.The present results show that the absorption coefficients of MoS₂ and MoSe₂ monolayers in the infrared region can be significantly enhanced by the adsorption Li atoms,and the enhancement is continuously strengthened with the increase of the concentration,which implies that the Li-covered MoS₂ and MoSe₂ monolayers can be an effective infrared material.