Enhanced thermoelectric performance of Janus Sn2PAs monolayer compared with its parents of SnP and SnAs

Abstract 2D Janus semiconductors with broken mirror symmetry and low-dimensional quantum confinement effect have attracted much attention, but most of them exhibit thermoelectric performance between their parents. Here, we explore the electron and phonon transport mechanism of monolayer SnP, SnAs and their Janus Sn2PAs based on first-principles and Boltzmann transport theory. In terms of electronic transport, the n-type doping presents obvious anisotropy, while the p-type doping gradually approaches isotropy from parents to their Janus structure. Importantly, different to usual Janus monolayers which lattice thermal conductivity is between those of their parents, Janus Sn2PAs has the lower lattice thermal conductivity than both its parents due to the competition between the moderate phonon group velocity and the short phonon relaxation time in Sn2PAs. The weaker anharmonicity but more three-phonon scattering channels lead to the short phonon relaxation time. Ultimately, the moderate power factor and the low lattice thermal conductivity make the optimal figure of merit of Janus Sn2PAs higher than those of its parents, reaching 1.41, 1.32 and 1.02 at 700 K for n-type Sn2PAs, SnP and SnAs, respectively. This work highlights the potential thermoelectric applications for Janus Sn2PAs, and will stimulate broad study on this class of 2D Janus thermoelectric materials.