Ultralow lattice thermal conductivity induced high thermoelectric performance in the δ-Cu2S monolayer

Abstract

Motivated by the recent experimental exfoliation of β-Cu₂S thin films and the theoretical finding of a new phase labeled the δ-Cu₂S monolayer, we carried out extensive studies on thermal conductivity and thermoelectric properties of the new phase using first principles combined with Boltzmann transport theory, focusing on the analysis of group velocities, Gruneisen parameters, three-phonon scattering rates, and the scattering phase space. Our results show that the δ-Cu₂S monolayer exhibits an intrinsically ultralow lattice thermal conductivity of 0.10 W m⁻¹ K⁻¹ at 800 K. Such an ultralow lattice thermal conductivity leads to a high thermoelectric figure of merit ZT = 1.33 at 800 K in an optimum p-type doping concentration, which is not only larger than the value of 1.23 in In₂S₃ doped Cu₂S at 850 K but also comparable with the value of 1.7 in Cu_1.97S at 1000 K, exhibiting good potential in thermoelectric applications.