Ultralow lattice thermal conductivity and high thermoelectric performance of monolayer KCuTe: a first principles study

Abstract

Monolayer KCuTe is a new-type of two-dimensional (2D) semiconductor material with high carrier mobility and large power energy conversion efficiencies, suggesting its potential application in thermoelectric (TE) and photoelectric fields. Based on the density functional theory (DFT) and semiclassical Boltzmann transport equation, the electronic and phonon transport properties of monolayer KCuTe are systematically studied. Our results show that it possesses an ultralow lattice thermal conductivity value of nearly ∼0.13 W m⁻¹ K⁻¹ at 300 K, mainly attributed to its small phonon group velocity, large Grüneisen parameters, and strong phonon–phonon scattering. Furthermore, the intralayer opposite phonon vibrations greatly restrict the heat transport. Monolayer KCuTe shows an ideal direct band gap of ∼1.21 eV, and a high twofold degeneracy appearing at the Γ point gives a high Seebeck coefficient of ∼2070 μV K⁻¹, leading to high TE performance. Using the transport coefficients together with constant electron relaxation time, the figure of merit (ZT) can reach 2.71 at 700 K for the p-type doping, which is comparable to the well-known TE material SnSe (2.6 ± 0.3 at 935 K). Our theoretical studies may provide perspectives to TE applications of monolayer KCuTe and stimulate further experimental synthesis.