Chirality as a Structural Degree of Freedom in Halide Perovskites

Abstract Chirality in halide perovskites has traditionally been associated with the incorporation of intrinsically chiral molecular components. Here, we develop a broader perspective in which chirality can emerge from the collective structural organization of an otherwise achiral inorganic lattice. We distinguish the structural origins of chirality, including molecular or ligand-mediated interactions, cooperative lattice distortions, surfaces and interfaces, and dynamic structural fluctuations, from the thermodynamic and structural parameters that control these states, including strain, dimensionality, confinement, temperature, pressure, and composition. Particular emphasis is placed on distinguishing structural distortion and inversion symmetry breaking from genuine chirality, which requires the absence of all improper symmetry operations and sufficient spatial correlation of the handed structural state. Two halide perovskite systems, Cs2PbI2Cl2 nanoplatelets and CsPbBr3 nanorods, illustrate complementary examples in which structural perturbations are associated with pronounced chiroptical responses. We further outline experimental criteria for establishing structural chirality and discuss opportunities for selecting, switching, and coupling handed structural states to optical, electronic, spin, and magnetic functionalities.