Manipulation of crystal symmetry is an important strategy to tune the thermoelectric performance. High-symmetry thermoelectric materials benefit from high band degeneracy. With first-principles calculations and Boltzmann transport theory, we systematically investigate the electronic and phononic transport properties of rhombohedral GeSe with higher symmetry. At optimized carrier concentrations, the maximum power factors are found to be 5.86 mW m-1 K-2 for the p-type and 4.45 mW m-1 K-2 for the n-type, respectively. The high p-type power factor originates from the highly degenerated L and Σ bands and small energy offset between them, while the n-type one results from the weak electron-phonon coupling. More importantly, rhombohedral GeSe possesses anisotropic and low lattice thermal conductivities of 3.58 W m-1 K-1 and 1.96 W m-1 K-1 at room temperature in the intralayer and interlayer directions, respectively, which is associated with the giant phonon anharmonicity driven by the resonant bonding. Combining the high power factor and low thermal conductivity, the predicted ZT values for p-type and n-type doping can reach 2.02 and 2.37 at 800 K. This study offers insights into the thermal and charge transport properties in rhombohedral GeSe, and demonstrates that both p-type and n-type GeSe are potential high-performance thermoelectric materials.

中文翻译：

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菱面体GeSe热电性质的第一性原理研究。

操纵晶体对称性是调节热电性能的重要策略。高对称热电材料得益于高频带简并性。通过第一性原理计算和玻耳兹曼输运理论，我们系统地研究了具有较高对称性的菱面体GeSe的电子和声子输运性质。在优化的载流子浓度下，p型最大功率因数为5.86 mW m-1 K-2，n型最大功率因数为4.45 mW m-1 K-2。高p型功率因数源自高度退化的L和Σ谱带以及它们之间的小能量偏移，而n型则由弱的电子-声子耦合产生。更重要的是，菱形GeSe具有3.58 W m-1 K-1和1的各向异性和低晶格热导率。在室温下，在层内和层间方向分别为96 W m-1 K-1，这与由共振键驱动的巨大声子非谐性有关。结合高功率因数和低热导率，p型和n型掺杂的ZT预测值在800 K时可以达到2.02和2.37。这项研究提供了对菱形GeSe的热和电荷输运性质的见解，并证明了p型和n型GeSe都是潜在的高性能热电材料。