Polar Solvent‐Assisted Chiral Ligand and Cation Exchange for Bright, Strongly Circularly Polarized Emission in CsPbBr ₃ Perovskite Nanoplatelets

Abstract Chiral semiconducting nanomaterials have recently garnered much interest, as their highly favorable chiroptical properties make them exceptional candidates for applications spanning optical communication, 3D displays, and secure encryption. However, their pronounced sensitivity to size, shape, and surface chemistry renders current processing methods highly inconsistent and uncontrollable, limiting further exploration toward these goals. Here, a method is devised to carefully induce and tune the chirality in perovskite nanoplatelets (NPLs) through a polar solvent‐assisted chiral ligand exchange while minimizing structural damage to the NPL lattices. Through solvent‐engineering, the anisotropic NPLs can also be coerced to self‐assemble into highly oriented superlattices, allowing for further control over the chiral NPLs' transition dipole moments. Together, these methods enable circularly polarized luminescence with dissymmetry factors as high as g _CPL = 3.4 × 10 ⁻² , representing an order of magnitude improvement over their solution‐state counterparts. Further, through simultaneous cation exchange with divalent transition metal ions, the quantum yield is successfully boosted by over an order of magnitude and enhance the solution g _CPL , demonstrating the versatility of this strategy. These results illustrate this highly general approach for finely tuning the chiroptical properties of perovskite nanomaterials through a single facile and efficient exchange step.