Tailoring Interfacial Electron Transfer in Au/S‐Cs ₂ SnI ₆ @Liquid Crystal Heterostructures for Enhanced Nonlinear Optical Property

ABSTRACT Tin‐based perovskites are promising lead‐free candidates for nonlinear optical applications, yet their performance and stability require further improvement. This work proposes a multi‐step interface engineering strategy to markedly enhance the nonlinear optical response. A stable Cs 2 SnI 6 (S‐Cs 2 SnI 6 ) film was first prepared via an improved in situ growth method, exhibiting an initial nonlinear absorption coefficient ( β ) of −4.12 × 10 −7 m W −1 . By replacing the conventional liquid crystal 4‐Cyano‐4’‐pentylbiphenyl (5CB) with the π ‐conjugated liquid crystal 4‐[(4‐Pentylphenyl)iminomethyl]benzonitrile (5CNB), an S‐Cs 2 SnI 6 @5CNB composite was obtained. The optimized interfacial interaction facilitated electron transfer, resulting in a significantly enhanced β value of 2.05 × 10 −6 m W −1 . Further incorporation of plasmonic gold nanoparticles (Au NPs) yielded the Au/S‐Cs 2 SnI 6 @5CNB heterostructure. Benefiting from the localized surface plasmon resonance (LSPR) of Au NPs, the local electromagnetic field was substantially intensified, boosting β value to 6.94 × 10 −6 m W −1 , a 239% increase over the composite without Au and a 434% increase over the control without the perovskite. Z‐scan measurements confirmed outstanding optical limiting with a low threshold of 0.072 J cm −2 . This study successfully demonstrates a synergistic enhancement strategy, paving the way for advanced optical limiters and nonlinear photonic devices.