Prominent Nonlinear Optical Absorption in SnS₂-Based Hybrid Inorganic–Organic Superlattice

Nonlinear optical materials hold great promise for applications in advanced opto-/opto-electronic devices. However, achieving a substantial nonlinear absorption coefficient and modulation depth concurrently remains challenging. This study proposes an effective strategy for enhancing the nonlinear optical response of materials through the construction of hybrid inorganic-organic superlattices via convenient organic intercalation. Synthesizing SnS2 intercalated with various tetra-alkylammonium cations, it is revealed that the optimized sample (SnS2/CTA: SnS2 intercalated with cetyltrimethylammonium, CTA(+)) exhibits a substantial enhancement of nonlinear absorption across a broad wavelength range (from 515 to 1550 nm) and for diverse nonlinear optical processes (saturable absorption, two-photon absorption, and three-photon absorption). Specifically, the SnS2/CTA demonstrates a third-order nonlinear absorption coefficient of (9.847 +/- 0.084) x 10(3) cm GW(-1) and a 69% modulation depth under laser excitation at 800 nm. Under 1550 nm excitation, it displays a fifth-order nonlinear absorption coefficient of (45.3 +/- 1.2) cm(3) GW(-2) and a 62% modulation depth. Notably, these values surpass those of the majority of non-exfoliated materials. Structural, spectral, and density functional theory calculations indicate no induced structure defects post-organic intercalation. The observed bandgap reduction is attributed to the electron injection associated with the organic molecule intercalation. The calculated performance enhancement, based on dielectric enhancement and bandgap reduction, qualitatively aligns with experimental findings.