Monolayer SnX (X = O, S, Se): Two-Dimensional Materials with Low Lattice Thermal Conductivities and High Thermoelectric Figures of Merit

Thermoelectric materials have attracted great attention due to their important applications in power generation, energy saving, and electric refrigeration. In this article, we designed three two-dimensional materials SnX (X = O, S, Se), which exhibit high stability. All three monolayers are direct band gap semiconductors with a “multivalley” characteristic in band structures, showing bandgaps of 2.87, 1.83, and 1.27 eV for SnO, SnS, and SnSe, respectively. In addition, the SnX monolayers with the optimum power factor values can be up to 0.91–0.97 W m–1 K–2 at room temperature. The small group velocities and strong anharmonic phonon behavior led to an intrinsic lattice thermal conductivity as low as ∼0.92–2.27 W m–1 K–1. As results, SnX exhibit excellent thermoelectric properties, with the figure of merit (ZT) up to ∼0.07–0.52, ∼0.13–0.89, and ∼0.25–1.41 for SnO, SnS, and SnSe at temperatures of 300–700 K, respectively.