Pressure‐Induced Structural and Optoelectronic Modulations in 2D Dion‐Jacobson Hybrid Lead Iodide Perovskites With a Rigid Spacer

Abstract 2D hybrid organic‐inorganic perovskites (HOIPs) are known for their superior chemical and thermal stability over 3D variants, positioning them as promising materials for advanced optoelectronic applications. Applying external high pressure is an effective strategy to modify their structures and tune their optoelectronic properties. This study examines the high‐pressure behavior of a Dion‐Jacobson type 2D HOIP, DPDAPbI₄, which incorporates the rigid organic spacer N,N‐dimethylphenylene‐p‐diammonium (DPDA). Utilizing photoluminescence, UV–visible absorption, vibrational spectroscopy, and in situ synchrotron powder X‐ray diffraction, an isostructural phase transition is identified near 1.5 GPa, marked by a notable shift in photoluminescence intensity linked to free exciton emission. Synchrotron X‐ray diffraction reveals significant anisotropic compression along the c‐axis, while structural analysis indicates the rare phenomenon of reduced lead‐iodide octahedral distortion below 2 GPa, contrasting with the increased octahedral distortion reported in most previous studies on lead‐based 2D HOIPs. Density functional theory calculations elucidate the structural origins and mechanisms driving the pressure‐induced phase transition and optoelectronic tuning. These findings underscore the critical interplay between rigid organic spacers and inorganic octahedra in modulating high‐pressure optoelectronic properties, offering valuable insights for designing future 2D HOIPs with tailored functionalities.