Stacking-Engineered Ultrafast Charge Separation in Type-I Silicane/Germanane van der Waals Heterostructures

Abstract Stacking engineering in van der Waals heterostructures offers a powerful route to modulating band alignment and carrier dynamics. Here, we present a theoretical investigation of SiH/GeH van der Waals heterostructures with different stacking configurations. Distinct stacking-dependent band alignments are identified, with the most stable stacking exhibiting a Type-I alignment and the others adopting Type-II alignments. Time-dependent density functional theory combined with regional natural hole/particle orbital analysis demonstrates that strong interlayer coupling between conduction bands enables photoinduced interlayer charge-transfer excitations even in the Type-I alignment. Nonadiabatic molecular dynamics simulations further uncover a pronounced asymmetry between photoelectron and -hole dynamics, leading to ultrafast electron transfer (∼0.5 ps) and long-lived hole localization (∼20 ps). These results reveal a functional charge-separation mechanism in Type-I heterostructures and establish stacking engineering for controlling excited-state dynamics.