For 2D transition metal dichalcogenides (TMDs), the layer thickness has a greater impact on its thermoelectric properties. Herein, the thermoelectric properties of Janus monolayer and bilayer HfSSe are studied based on first-principles calculations combined with Boltzmann equations, and the thermoelectric properties of bilayer HfSSe are also investigated with different stacking types. Owing to the influence of the interlayer coupling, the degradation of the phonon dispersion curve and the change of the phonon scattering intensity of the bilayer HfSSe lead to the decrease of its lattice thermal conductivity. In addition, the increase in the degeneracy of the electronic band structure of the bilayer HfSSe and the change in the density of states also change the thermoelectric transport properties of electrons. Integrating the coupling of high power factor and low thermal conductivity, the maximum ZT values at room temperature for n-type doping are predicted as 3.24 and 5.54 for monolayer and SeHfS/SHfSe, respectively. And the ZT values increase to 3.24 and 5.54 as the temperature increases to 600 K. The result manifests that both monolayer and bilayer HfSSe are promising thermoelectric materials, and the layer thickness and stacking types also significantly affect the thermoelectric properties of the 2D TMDs materials.

中文翻译：

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Janus 单层和双层 HfSSe 的高热电性能

对于二维过渡金属二硫属化物（TMDs），层厚对其热电性能的影响更大。在此，基于第一性原理计算结合玻尔兹曼方程研究了Janus单层和双层HfSSe的热电性质，并研究了不同堆叠类型的双层HfSSe的热电性质。由于层间耦合的影响，双层HfSSe的声子色散曲线退化和声子散射强度的变化导致其晶格热导率降低。此外，双层 HfSSe 电子能带结构简并性的增加和态密度的变化也改变了电子的热电传输特性。对于单层和 SeHfS/SHfSe，预测室温下 n 型掺杂的ZT值分别为 3.24 和 5.54。随着温度升高到 600 K ，ZT值分别增加到 3.24 和 5.54。结果表明，单层和双层 HfSSe 都是有前途的热电材料，层厚和堆叠类型也显着影响 2D TMDs 材料的热电性能。