Hydrostatic Pressure Control of Dimensionality in the DMAPbBr3 Lead Halide Perovskite for Tunable Optical Emission

Three-dimensional (3D) hybrid organic–inorganic perovskites (HOIPs) exhibit exceptional optoelectronic properties. However, 3D lead halide perovskites are known to have only a few small cations, although many organic cations that formally satisfy geometric criteria for 3D perovskite formation nevertheless stabilize lower-dimensional or hexagonal frameworks under ambient conditions. Here, we investigate the structural and optical response of dimethylammonium lead bromide (DMAPbBr3) under hydrostatic pressures up to 8.5 GPa. By combining high-pressure X-ray diffraction, Raman spectroscopy, photoluminescence, optical transmission, and density functional theory, we identify a sequence of pressure-induced structural transformations, including the most interesting reconstructive transition from a 4H-hexagonal phase to a 3D orthorhombic perovskite framework near 0.9 GPa. Pressure induces cation ordering and changes in octahedral connectivity, which accompany pressure-dependent color changes, strong band gap modulation, and emergence of free-exciton emission. Raman measurements after decompression indicate a partial recovery of the initial vibrational response. Density functional theory calculations support the experimental findings and elucidate how changes in the octahedral connectivity govern the electronic structure and optical response. These results establish hydrostatic pressure as an effective route for stabilizing 3D perovskite frameworks that are inaccessible under ambient conditions.