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具有低晶格热导率和高热电优值的二维(2D)材料可用于热电器件的制备。本文通过第一性原理和玻尔兹曼输运理论，系统地预测了单层Cu2X (X=S,Se)的热电性质。研究发现单层Cu2Se较Cu2S在室温下具有更低的晶格热导率(1.93W/mK和3.25W/mK)，这源于其更低的德拜温度和更强的非谐性。单层Cu2X (X=S,Se)价带顶处的能带简并效应显著增大了其载流子有效质量，导致p型掺杂下具有高的塞贝克系数和低的电导率。在最优掺杂浓度下，单层Cu2S (Cu2Se) n型的功率因数16.5mW/mK2(25.9mW/mK2)远高于其p型的功率因数1.1mW/mK2(6.6mW/mK2)，且随着温度的提升这一优势将更加明显。温度为700K时，单层Cu2S和Cu2Se在n型最优掺杂浓度下的热电优值可以达到1.85和2.82，高于p型最优掺杂浓度下的热电优值0.38和1.7。单层Cu2X (X=S,Se)的优良热电性能可与近期报道的许多先进的热电材料相媲美，特别是单层Cu2Se的热电优值高于众所周知的先进热电材料-单层SnSe (2.32)。因此，单层Cu2X (X=S,Se)是一类具有优异性能和良好应用前景的潜在热电材料。这些结果为后续探索2D热电材料的实验及应用提供了理论依据，并为深入了解声子热输运对热电优值的影响提供了新的见解。Two-dimensional (2D) materials with lower lattice thermal conductivity and high figure of merit are useful for applications in thermoelectric (TE) devices.In this work,the thermoelectric properties of monolayer Cu2X (X=S,Se) have been systematically researched through first-principles and Boltzmann transport theory.We have verified the dynamic stability of monolayer Cu2X (X=S,Se) through elastic constants and phonon dispersion.The results show that monolayer Cu2X (X=S,Se) together with small lattice constants,resulting in lower phonon vibration modes.Phonon transport calculations confirm that monolayer Cu2Se has lower lattice thermal conductivity (1.93W/mK) than Cu2S (3.25W/mK) at room temperature,which is due to its small Debye temperature and stronger anharmonicity.Moreover,the heavier atomic mass of Se atoms effectively reduces the phonon frequency,resulting in a ultra narrow phonon band gap (0.08THz) and lower lattice thermal conductivity for monolayer Cu2Se.The band degeneracy effect at the VBM of monolayer Cu2X (X=S,Se) significantly increases its carrier effective mass,resulting in higher Seebeck coefficient and lower conductivity under p-type doping.The electric transport calculation at room temperature shows that the conductivity of monolayer Cu2S (Cu2Se) under n-type doping about 1011cm-2 is 2.8×104S/m (4.5×104S/m),obviously superior to their conductivity about 2.6×102S/m (1.6×103S/m) under p-type doping.At the optimum doping concentration for monolayer Cu2S (Cu2Se),the n-type power factor is 16.5mW/mK2(25.9mW/mK2),which is far higher than p-type doping 1.1mW/mK2(6.6mW/mK2).Through the above results,the excellent figure of merit of monolayer Cu2S and Cu2Se under optimal n-type doping at 700 K can approach 1.85 and 2.82,which are higher than 0.38 and 1.7 under optimal p-type doping.The excellent thermoelectric properties of monolayer Cu2S and Cu2Se are comparable to those of many promising thermoelectric materials reported recently.Especially,the figure of merit of monolayer Cu2Se is larger than the well-known high-efficient thermoelectric monolayer SnSe (2.32).Therefore,monolayer Cu2X (X=S,Se) are potential thermoelectric material with excellent performance and good application prospects.Such results provide theoretical basis for the follow-up experiments exploring the practical applications of 2D thermoelectric semi-conductors materials and offer an in-depth insight into the effect of phonon thermal transport on improvement of TE transport properties.
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Keywords:
- First-principles /
- Conductivity /
- Thermal conductivity /
- Thermoelectric
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