2D plane XP2 (X = Ni, Pd, Pt) with narrow band gaps, ultrahigh carrier mobility and high electrical transport performance

Abstract

Based on state-of-the-art first principles calculations, we proposed three plana-pentagon monolayers, namely, NiP2, PdP2 and PtP2. The monolayers are direct band-gap semiconductors with band gaps of 0.66 eV, 0.68 eV and 0.40 eV. In addition, XP2 (X = Ni, Pd, Pt) simultaneously showed ultrahigh electron and hole mobilities, up to ∼105 cm2·V−1·s−1, resulting in high electrical transport performance with thermoelectric power factors of 102–103 mW·K−2·m−1. Additionally, due to the high group velocities and phonon lifetimes, monolayer XP2 has thermal conductivities of 21.73, 10.43 and 25.13 Wm−1 K−1 for NiP2, PdP2 and PtP2, respectively. As results, the monolayers exhibit favourable ZT values, ranging from 0.08–0.45 at temperatures of 300–700 K.