Boosted Chirality Transfer in 2D Perovskites through Structural Isomer‐Driven Halogen–Halogen Interaction

Abstract Chiral perovskites are promising materials due to their unique ability to interact with circularly polarized light (CPL), offering great potential in advanced photonic and spintronic applications. However, specific design principles for highly chiroptically active chiral perovskites remain unclear, hindering their practical exploitation. In this study, chiral cation fluorinated isomerization approach is employed to enhance the chiroptical response of chiral perovskites. Specifically, it is systematically discovered that incorporating ortho ‐fluorinated chiral cations instead of para ‐fluorinated cations induces a strong organic–inorganic halogen–halogen interaction due to the unique spatial arrangement. This boosted chirality transfer, mediated by the strong halogen–halogen interaction, resulting in a fivefold improvement in the circular dichroism compared to its para‐fluorinated counterpart. Consequently, a CPL photodetector utilizing the ortho ‐fluorinated chiral perovskite exhibited superior CPL distinguishability of 0.288, the highest value among 2D lead‐iodide perovskite‐based devices. Furthermore, the photodetector incorporating these structural isomers demonstrated extended operational stability as well as high photodetecting performance.