Engineering Chirality in Halide Perovskites

The ability to control chirality in halide perovskites offers new opportunities for circularly polarized photonics, spin-selective electronics, and quantum information technologies. Chirality in halide perovskites is commonly achieved through chiral molecular building blocks or externally imposed photonic architectures. Although both approaches can generate strong chiroptical responses, many spin-dependent functionalities require structural symmetry breaking embedded within the material itself. Here we show that chirality can emerge directly during crystal growth. By combining glancing angle deposition with controlled substrate rotation, we generate highly textured PbI2 nanostructures with growth-controlled crystallographic torsion. X-ray texture analysis reveals that substrate rotation progressively rotates the crystal orientation during growth while preserving the c-axis orientation, resulting in a twisted texture with giant and tuneable chiroptical responses, including ellipticities of 19{\deg} and absorption dissymmetry factors approaching 0.6. The chirality programmed during growth is transferred through vapour-phase conversion into multiple halide perovskite compositions, resulting in circularly polarized luminescence with glum values up to 0.23. These findings establish growth-controlled crystallographic torsion as a previously unexplored origin of chirality in halide perovskites.