First-principles study on bilayer SnP₃ as a promising thermoelectric material

The bilayer SnP₃ is recently predicted to exfoliate from its bulk phase, and motivated by the transition of the metal-to-semiconductor when the bulk SnP₃ is converted to the bilayer, we study the thermoelectric performance of the bilayer SnP₃ using first-principles combined with Boltzmann transport theory and deformation potential theory. The results indicate that the bilayer SnP₃ is an indirect band gap semiconductor and possesses high carrier mobility. The high carrier mobility results in a large Seebeck coefficient observed in both n- and p-doped bilayer SnP₃, which is helpful for acquiring a high figure of merit (ZT). Moreover, by analyzing the phonon spectrum, relaxation time, and joint density of states, we found that strong phonon scattering makes the phonon thermal conductivity extremely low (∼0.8 W m^-1 K^-1 at room temperature). Together with a high power factor and a low phonon thermal conductivity, the maximum ZT value can reach up to 3.8 for p-type doping at a reasonable carrier concentration, which is not only superior to that of the monolayer SnP₃, but also that of the excellent thermoelectric material SnSe. Our results shed light on the fact that bilayer SnP₃ is a promising thermoelectric material with a better performance than its monolayer phase.