Electronic and Thermoelectric Properties of Transition-Metal Dichalcogenides

Abstract

Using first-principles electronic structure calculations performed within the B1-WC hybrid functional, we study the thickness and strain dependency of electronic and thermoelectric (TE) properties of transition-metal dichalcogenides (TMDs). We consider both 2H (MoS 2 , MoSe 2 , MoTe 2 , WS 2 , WSe 2 , WTe 2 ) and 1T (SnS 2 , SnSe 2 , HfS 2 , HfSe 2 , HfTe 2 , ZrS 2 , ZrSe 2 ) structures and identify those TMDs with a high TE potential (WSe 2 , MoTe 2 , and SnSe 2 ). The thickness and strain significantly change the electronic properties near the forbidden band gaps. We rationalize at an atomic level these changes in terms of the interplay between in-plane bonding/antibonding X− X(M−M) interactions through sp 2 hybridization and the stronger antibonding/ nonbonding M−X interactions due to sp 3 d and sp 3 d 2 hybridizations inside TMD layers (X, chalcogen; M, transition metal, Sn). Thickness and in-plane strain appear as effective ways to tune electronic band structures, increase the degeneracy of carrier pockets, and optimize the TE properties of TMDs. We estimate the anisopropy of carrier pockets and introduce the effective mass quality factor B m for the maximization of TE performance at a given carrier density and temperature. High-potential TMDs have B m and power factors comparable to PbTe and Bi 2 Te 3 .

Optimization of the Thermoelectric Properties of SnSe2 Using First-Principles Calculations

“…In Figure a, the DFT band structure is plotted. The conduction band minimum (CBM) of SnSe 2 lies at the L-point, and the valence band maximum lies along the Γ–K direction in the Brillouin zone, denoting the indirect band gap of SnSe 2 . ,, The conduction band is highly dispersive along Γ–M or Γ–K directions (in-plane directions) than in the Γ–A direction (cross-plane direction), indicating lower electron effective mass along in-plane directions. The inclusion of vdW interactions has minimal effects on the electronic band structure.…”

Recent Progress of Two-Dimensional Transition Metal Dichalcogenides for Thermoelectric Applications

“…One of the most important phenomena is direct-to-indirect band gap transition induced by tensile strain [82][83][84][85][86][87][88] (in the case of WSe 2 , tensile strain induces an indirect-to-direct band gap transition [87,88]). In the meantime, strain also modulated the band gap, effective mass, and valley degeneracy at conduction/valance band edges of TMDs, leading to strain-tunable electrical conductivity and correlated TE properties [89,90]. For n-type WS 2 , the relaxation time scaled power factor (S 2 σ/τ) was increased by the application of compressive strain, whereas for p-type WS 2 , it was increased with the application of tensile strain due to valley degeneracy [91].…”

Dual‐Site Doping and Low‐Angle Grain Boundaries Lead to High Thermoelectric Performance in N‐Type Bi2S3

“…[ 24 ] Additionally, stress engineering is a widely used method to tune the physical properties of a given material, which can modulate the band gap, effective mass, and valley degeneracy at conduction/valance band edges. [ 25 ] Meanwhile, tensile strain can soften the phonons, decreasing the phonon group velocity, and thus leading to a reduced thermal conductivity. [ 26 ] However, strain‐tunable electron/phonon transport is usually achieved in 2D materials with their large stretchability, bendability, and foldability or in 3D bulk samples at high pressure.…”