Interfacial Charge-Transfer Dynamics in Type-II Mg₁In₂Se₄/Sb van der Waals Heterostructures for Optoelectronics

Two-dimensional (2D) semiconductors are highly promising for advanced optoelectronics but are fundamentally limited by strong excitonic binding and unbalanced carrier transport. Here, we design a Mg₁In₂Se₄/Sb van der Waals heterostructure that simultaneously overcomes these bottlenecks through synergistic thermodynamic and kinetic engineering. First-principles and many-body perturbation calculations reveal that an intrinsic Type-II band alignment coupled with enhanced interfacial dielectric screening significantly reduces the exciton binding energy to 0.289 eV, yielding robust visible-light absorption (>10⁵ cm^–1). Crucially, nonadiabatic molecular dynamics simulations uncover a striking five-order-of-magnitude time scale separation between ultrafast interfacial charge transfer (134.1–155.6 fs) and much slower nonadiabatic recombination (68.44 ns), thereby favoring efficient carrier extraction before recombination. Device-level quantum transport further predicts a polarization-sensitive photoresponsivity of up to ∼160 mA/W, and Scharber-model analysis indicates that external modulation can increase the theoretical power conversion efficiency from 10.87% to 17.37%. By establishing a clear kinetic criterion for efficient charge separation, this work provides a theoretically guided design blueprint for next-generation high-efficiency 2D optoelectronic and energy-harvesting devices.