Excitonic landscape and quasi-type-I nature in Moiré supercells of Ti-based MXene-MoS2 van der Waals heterostructures

Van der Waals heterostructures based on MXenes and transition metal dichalcogenides offer a versatile platform for engineering excitonic and optoelectronic properties. However, accurate prediction of their behavior is non-trivial; we highlight that reliance on standard 1 × 1 models of lattice-mismatched systems introduces artificial strain, creating a significant risk of misattributing computational artifacts to intrinsic interface physics. Here, we present a comprehensive first-principles investigation of Ti 2 CO 2 /MoS 2 and Ti 3 C 2 O 2 /MoS 2 heterostructures, employing many-body perturbation theory (GW-BSE) to benchmark the computationally efficient TD-HSE06 + Δ methodology for realistic, strain-relaxed Moiré supercells. Our analysis reveals a distinct “quasi-type-I” optoelectronic character for these systems. We show that advanced methods are indispensable for MXene/MoS 2 heterostructures, as basic electronic structure predictions yield an incomplete picture: although the bands exhibit a type-II staggered alignment with the valence band maximum localized on the MoS 2 and the conduction band minimum on the MXene, the theoretically lowest-energy interlayer transitions are rendered effectively dark due to negligible wavefunction overlap. Consequently, the optical landscape is dominated by bright intralayer excitons confined within the MXene layer. Therefore, while the type-II band alignment allows for subsequent non-radiative charge separation, the initial direct optical generation and radiative recombination of interlayer excitons are highly suppressed. This unique decoupling suggests these heterostructures can function as robust platforms where the bright optical transitions of the MXene are preserved, while still participating in ultrafast non-radiative interfacial charge dynamics.