Transport properties and photoresponse of a series of 2D transition metal dichalcogenide intercalation compounds

Abstract

A series of 2D transition metal dichalcogenide (TMD) intercalation compounds, PdCl₂/PtCl₂@MX₂ (M = Mo, W; X = S, Se), formed by covalently intercalating PdCl₂/PtCl₂ into the bilayer space of MX₂, have been designed and investigated using density functional theory (DFT) and non-equilibrium Green's function (NEGF) methods. The intercalation compounds adopt a planar quadridentate coordination structure of PdCl₂X₂/PtCl₂X₂. The possibility of electron–hole recombination is enhanced because of the introduction of the PdCl₂/PtCl₂ groups, and on the other hand, the PdCl₂/PtCl₂-derived HOMO and LUMO are shielded well by the MX₂ band gap, both of which are beneficial for improving the fluorescence quantum yield. The conductivity of the intercalation compounds is slightly lowered owing to the trap effect of PdCl₂/PtCl₂. In addition, electron transportation is easier along the zigzag direction than along the armchair direction. Contrary to the conductivity, a robust photogalvanic effect (PGE) can be observed when linearly polarized light is applied onto the PdCl₂/PtCl₂ groups, and the armchair direction exhibits a much higher photoresponse compared with the zigzag direction. The largest photocurrent could reach up to 1.83 × 10⁻² a₀² per photon. For a given MX₂, the PdCl₂ groups induce a higher maximum photocurrent than the PtCl₂. Significantly, the photocurrent is highly dependent on the polarization angle θ and the applied photon energy, making the intercalation compounds appealing for designing photoresponse on/off switches by tuning θ or photon energy. Our simulation frameworks as well as the results offer guidelines for novel 2D functional device design and fabrication.