Photoinduced Interfacial Charge Transfer Tailors Second-Harmonic Generation in NbSe2-MoS2 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.