Fig. 1

Refinement of the precursor crystal structure. a GIXRD of precursor film plotted as Q (scattering vector) vs. χ (azimuthal scattering angle). Apparent arcs are layer lines indexed to (hk1) and (hk2) reflections. b Refined model and diffraction data for l = 1 and l = 2 layer lines. c Refined precursor framework: 1D chains with layers of 4 corner-sharing lead-halide octahedra, halides are shown only as iodine and MA+ cations are omitted for clarity. d Refined precursor unit cell, MA⁺ cations (cyan spheres) are added to preserve charge balance. Axial halide sites are colored green to emphasize probable Cl occupancy