| Summary: | Based on the first-principles of density functional theory and Boltzmann transport theory, we report two-dimensional (2D) α -Se _2 Te monolayer to be a high-performance medium temperature p-type thermoelectric material with low lattice thermal conductivity ( κ _l ), high power factor ( PF ) and high dimensionless figure of merit ( ZT ). At the temperature of 700 K, PF is up to 3.77 and 11.5 mW m ^−1 K ^−2 , ZT is up to 0.55 and 1.91 in appropriate doping level for n- and p-types, respectively, and k _l is as low as 2.09 W m ^−1 K ^−1 . We also examine the effect of spin-orbital coupling (SOC) on the carrier transport and find that with SOC, PF and hence ZT will be reduced significantly due to the reduced band gap. The higher PF of p-type than that of n-type is evidently due to the flatter valence band edge than conduction band edge. Low k _l is inevitably attributed to the strong lattice anharmonicity.
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