Monolayer Ag₂S: Ultralow Lattice Thermal Conductivity and Excellent Thermoelectric Performance

For efficient thermoelectric materials, high power factor and low lattice thermal conductivity are desired properties. Therefore, the high lattice thermal conductivity of two-dimensional materials limits their usage in thermoelectric applications. We employ first-principles calculations along with semiclassical Boltzmann transport theory for the electron and phonon dynamics to investigate the thermoelectric properties of nonmetal-shrouded monolayer Ag2S. We show that the simultaneous presence of flat and dispersive bands in the vicinity of the conduction band edge leads to a high power factor, while close proximity of the acoustic and optical bands in the phonon dispersion results in low thermal conductivity. With moderate electron doping, a high in-plane thermoelectric figure of merit is achieved. Our results demonstrate great potential of nonmetal-shrouded monolayer Ag2S in thermoelectric applications.