Theoretical Study of a Novel WSi₂N₄/MoSi₂N₄ Heterostructure with Ultrafast\nCarrier Transport

Abstract

Promoting\ncarrier separation and migration is the key factor to\nimprove photocatalytic performance. In this work, we proposed a novel\nWSi₂N₄/MoSi₂N₄ heterostructure\nincluding six different stacking configurations, in which the AB stacking\nconfiguration is thermodynamically most stable and can satisfy the\nrequirement of overall water splitting. The presence of an internal\nelectric field owing to the symmetry breaking will promote the carrier\nseparation to different layers, and the low exciton (e–h pairs)\nbinding energy (0.12 eV) and high carrier mobility further boost the\nseparation and migration of electrons and holes; these results demonstrate\nthat heterojunctions have high carrier activity and good photocatalytic\nperformance. The high light absorption coefficient (∼10⁵ cm^–1) and enhanced visible light absorption\nalso further support our theoretical predictions. Moreover, the research\nof nonadiabatic molecular dynamics provides a deeper understanding\nthat the time of carrier transfer is much longer than e–h recombination\n(2420 fs for electrons, 67 ns for e–h recombination) and its\nintrinsic photocatalytic mechanism. These findings indicated that\nAB stacking with ultrafast carrier transport is an excellent photocatalyst.