Comparative Study of Thermoelectric Performance in InP3 and SnP3 Monolayers: Role of Electronic Structure and Lattice Dynamics

Abstract

We conduct a detailed comparative investigation of the structural, electronic and thermal transport properties of monolayer InP₃ and SnP₃ based on first-principles calculations combined with Boltzmann transport theory. Both systems exhibit indirect semiconducting behaviour, however, their distinct electronic dispersion led to markedly different transport responses. InP₃ displays a pronounced DOS enhancement near the valence band maximum, which yields a larger Seebeck coefficient, thereby favouring p-type thermoelectric performance. Conversely, SnP₃ shows a higher DOS near the conduction band edge and intrinsically larger carrier concentration, resulting in significantly enhanced electrical conductivity. Additionally, notable phonon softening and bonding heterogeneity in SnP₃ suppress the lattice thermal conductivity, further improving thermoelectric efficiency. As a result, SnP₃ achieves a superior p-type figure of merit, reaching ZT ≈ 0.74 at 600 K, whereas InP₃ exhibits comparatively improved n-type performance due to its higher Seebeck coefficient. These results highlight the role of band-edge DOS engineering and phonon softening in optimizing thermoelectric behaviour in two-dimensional triphosphides.