Photoinduced Interfacial Charge Transfer Tailors Second-Harmonic Generation in NbSe ₂ –MoS ₂ Heterostructures

Effective modulation of ultrafast nonlinear optical properties in two-dimensional materials is essential for advancing nanophotonic technologies. In this work, we demonstrate precise control over the ultrafast carrier dynamics in NbSe₂ by tailoring the nanosheet thickness and constructing a van der Waals heterostructure with MoS₂. Transient absorption measurements reveal that carrier lifetimes extend from several to hundreds of picoseconds with increasing layer thickness, due to interlayer coupling. More importantly, interfacial charge transfer from MoS₂ to NbSe₂ in the heterostructure further prolongs carrier relaxation and significantly enhances the second harmonic generation (SHG) response. First-principles calculations attribute this SHG enhancement to a symmetry-breaking electronic imbalance induced by charge redistribution at the interface. These findings establish interfacial charge engineering as a powerful and general strategy for tailoring ultrafast nonlinear optical properties in 2D materials, offering new pathways for designing high-performance optoelectronic devices.