Local Symmetry Breaking in 3D Hybrid Perovskites with 3-Hydroxyazetidinium

Two-dimensional (2D) hybrid perovskite semiconductors with nonprimary ammonium cations (NPACs) have recently attracted interest for spin-optoelectronics owing to the symmetry-breaking distortions in their crystal structures. However, implementing this design strategy in three-dimensional (3D) analogs remains largely unexplored, primarily due to stricter restrictions on cation size. Here, we introduce a family of 3D hybrid perovskites (3DHPs), ASnX 3, where A = 3-hydroxyazetidinium (AzOH; + NH 2 (CH 2 ) 2 CHOH) and X = Cl, Br, and I. The choice of a bulky NPAC, coupled with the incorporation of a polar group (−OH), targets broken symmetry within the 3D frameworks. While single-crystal X-ray diffraction analysis reveals spatially averaged centrosymmetric cubic (i.e., Pm -3 m space group) unit cells, with the largest lattice parameters among existing ASnX 3 analogs, first-principles molecular dynamics and electronic structure calculations indicate that the relatively fixed dipoles of AzOH within the SnX 6 -derived framework introduce local inversion asymmetry and spin polarization. By incorporating a polar cation with limited mobility into the 3D perovskite framework, (AzOH)SnX 3 unlocks potential for spin-optoelectronics, photovoltaics, ferroelectrics, and nonlinear optics.