Phase Transitions in Dimer/Layered Sb‐Based Hybrid Halide Perovskites: An In‐Depth Analysis of Structural and Spectroscopic Properties

Abstract When used as the active layers—either as a light absorber in photovoltaic devices or as an electroluminescent material in light‐emitting devices—lead‐free perovskites significantly impact the performance of optoelectronic devices. This study focuses on antimony‐based perovskites, which are promising for lighting applications. These types of perovskites enable the formation of self‐trapped excitons (STEs) with higher dissociation energy than lead‐based perovskites, which generate excitons with lower dissociation energy. The (CH ₃ NH ₃ ) ₃ Sb ₂ I ₉ crystals are synthesized using two methods, resulting in distinct spatial configurations – dimer and dimer/layered mixtures, each exhibiting unique structural and spectroscopic properties, as revealed by comprehensive multi‐parametric complementary analyses. Their emissive properties underscore the efficiency of the STE photoluminescence, driven by electron–phonon interactions and influenced by Sb‐Sb distances in (CH ₃ NH ₃ ) ₃ Sb ₂ I ₉ powder, whether dispersed in polymethyl‐methacrylate or solution. The phase transition from monoclinic to hexagonal (dimer) and trigonal (layered) structures enabled the tuning of the optical properties in direct correlation with the structural and electrical features. The photoluminescence behavior of the STEs, analyzed in conjunction with the Raman spectroscopy, elucidates the dynamic process of the electron‐phonon coupling effects in the dimer (face‐capping Sb–I octahedra) and layered (corner‐sharing Sb–I octahedra) crystallographic structures.