Interfacial dipolar interactions drive giant second-harmonic generation in 2D organic–inorganic heterostructures

Interfacial coupling governs the emergent functionality of two-dimensional (2D) organic–inorganic heterostructures, underpinning advances in linear optoelectronics such as photovoltaics. However, extending this control to the nonlinear optical regime remains elusive, as it requires driving the coherent nonlinear polarization of the inorganic lattice using molecular states, which is distinct from the incoherent charge transfer exploited in linear devices. Here we report a giant second-harmonic generation (SHG) response driven purely by long-range interfacial dipolar interactions in an α-perylene organic crystal (α-Pe)/WS2 heterostructure. We show that the specific crystalline anisotropy of the organic layer creates a polarization-tunable antenna, where anisotropic dipole–dipole coupling efficiently channels excitation energy into the WS2 layer to drive the nonlinear process. This mechanism yields a spatially uniform, giant effective second-order susceptibility χ _eff ⁽²⁾ approaching ~20 nm V ^-1 in monolayers and, notably, induces interfacial symmetry breaking to activate robust SHG in nominally centrosymmetric bilayer WS2. Our results establish organic–inorganic interfacial coupling as a generalizable lever for engineering nonlinear optical responses; given the vast abundance of molecular crystals with distinct dipolar symmetries, this strategy offers a scalable route to compact, chemically designable on-chip nonlinear photonic systems.