Interlayer coupling in tri-layered van der Waals heterostructures of MX2 (M = Mo, W; X = S, Se, Te) monolayers: optical and photocatalytic response

Abstract

Electronic structure, optical and photocatalytic properties of tri-layered van der Waals heterostructures (vdWHs) composed of MX₂ (M = Mo, W; X = S, Se, Te) monolayers are investigated via first principles (hybrid) calculations. Both the dynamical and thermal stabilities of these systems are confirmed via binding energies, phonon spectrum calculations and AIMD simulations. The electronic band structures show that MoS₂/MoSe₂/WS₂ (MoSe₂/MoS₂/WSe₂) and MoS₂/WSe₂/WS₂ (MoSe₂/WS₂/WSe₂) vdWHs are Γ–K (K–K) indirect(direct) bandgap semiconductors, while strain engineering changes MoS₂/WSe₂/WS₂ to a direct bandgap semiconductor. The carrier effective mass calculated by parabolic fitting of the CBM shows a small effective mass with higher carrier mobility in the MoS₂/WSe₂/WS₂ vdWH. Charge density difference and Bader charges were analyzed to investigate the qualitative and quantitative behaviour of the transfer of charges among the layers of the vdWHs. A blue shift is observed in the position of excitonic peaks when the chalcogen atom becomes heavier (Mo–W) in the middle layer of the vdWHs, whereas a red shift occurs by applying compressive strain in MoS₂/WSe₂/WS₂ vdWHs. Furthermore, a strong absorption from infrared to visible light is observed.