Geometry and Greatly Enhanced Thermoelectric Performance of Monolayer MXY Transition‐Metal Dichalcogenide: MoSTe as an Example

Abstract

2D thermoelectric materials with a high power factor and low lattice thermal conductivity have recently been the focus of cutting‐edge research. Herein, combining first‐principles calculations and semiclassical Boltzmann transport theory, a structural search on the monolayer transition‐metal dichalcogenide MoSTe is conducted and its electronic structure, lattice dynamics, and thermoelectric properties are carefully studied. A new tetragonal blend structure is found that is both energetically and dynamically more stable than the experimentally synthesized hexagonal Janus structure, and this blend structure possesses strong anisotropic in‐plane electron and phonon transport properties. Both structures have insulating ground states, which allow a reasonable Seebeck coefficient. Phonon dispersion reveals that several optical phonon‐branches downshift and overlap with the acoustic branches, leading to an enhanced scattering rate, greatly reduced lattice thermal conductivity, and eventually excellent thermoelectric performance with = 0.34 at 300 K and 1.0 at 600 K for the blend‐MoSTe. The results demonstrate the great potential of the monolayer MXY transition‐metal dichalcogenide in thermoelectric applications.

Layered 2D MoSe2(1–x)Te2x Alloys: Promising Thermoelectric Material with Tunable Thermal and Electrical Transport

“…The thermal conductivity values observed for the monolayer alloys of MoSe 2(1– x ) Te 2 x are lower than that of pristine MoSe 2 and MoTe 2 , and the lowest thermal conductivity is obtained for x = 0.5. These data closely match the predictions made in a previous report for the alloy systems. , Since phonons are known to localize on defects and strain in the material, it is plausible that the lowest thermal conductivity of MoSe 1.0 Te 1.0 may be attributed to a maximum substitutional disorder. The phonon scattering plays an important role in determining the thermal conductivity.…”

“…These data closely match the predictions made in a previous report for the alloy systems. 37,38 Since phonons are known to localize on defects and strain in the material, it is plausible that the lowest thermal conductivity of MoSe 1.0 Te 1.0 may be attributed to a maximum substitutional disorder. The phonon scattering plays an important role in determining the thermal conductivity.…”

“…Alloying of TMDs could potentially lead to highly efficient thermoelectric materials where it is possible to successfully reduce the thermal conductivity and alter the band structure. 37,38 This approach to band engineering has been successfully demonstrated in a large range of 2D alloys such as MoSTe, WSTe, WSSe, WSeTe, and others. 28,37−39 Replacement of Se by a heavier element, Te, is likely to enhance the scattering of phonons and thus leads to a significant decrease in thermal conductivity.…”

“…This involves optimizing the band gap, altering the electronic density of states, and converging the valence or conduction bands to maximize charge carrier mobility and concentration, thereby boosting the overall thermoelectric performance. Alloying of TMDs could potentially lead to highly efficient thermoelectric materials where it is possible to successfully reduce the thermal conductivity and alter the band structure. , This approach to band engineering has been successfully demonstrated in a large range of 2D alloys such as MoSTe, WSTe, WSSe, WSeTe, and others. ,− Replacement of Se by a heavier element, Te, is likely to enhance the scattering of phonons and thus leads to a significant decrease in thermal conductivity. Moreover, it has been suggested that alloying with Te leads to an increase in the effective mass m * of charge carriers, change in the density of states, and hence improvement in their electronic properties .…”

Recent progress on two-dimensional van der Waals heterostructures for photocatalytic water splitting: a selective review

“…However, the charge-carrier mobility exhibited by Janus TMD nanolayers (e.g. 71.21 cm 2 V −1 s −1 (163.52 cm 2 V −1 s −1 ) for electrons (holes) of MoSSe [186]; 27.64 cm 2 V −1 s −1 (65.43 cm 2 V −1 s −1 ) for electrons (holes) of MoSTe [187]) is not satisfactory; some of them are not yet favored over the pristine TMD materials [62]. Nevertheless, Janus TMDs are better for photocatalytic water splitting than TMDs owing to the built-in electric field induced low rate for e-h recombination [178,181,188], ultra-long carrier lifetime (e.g.…”