Beyond the Cubic Phase: Pressure‐Induced Bandgap Modulation in a CH ₃ NH ₃ PbBr ₃ Perovskite at Low Temperatures

Abstract Recent investigations into the bandgap evolution of hybrid perovskites under hydrostatic pressure have primarily focused on the room‐temperature cubic phase of methylammonium lead bromide (MAPbBr 3 ), leaving its low‐temperature behavior largely unexplored. In this work, the pressure response of MAPbBr 3 single crystals is investigated over a broad temperature range using photoluminescence (PL), cathodoluminescence (CL), and density functional theory (DFT) calculations. Hydrostatic pressure is shown to modify the electronic structure of MAPbBr 3 across cubic (280 K, 260 K), tetragonal (210, 170 K), and orthorhombic (120, 80 K) phases, quantified via the bandgap pressure coefficient ( α ). The experimentally obtained α values are: α 280K,260K = −47 ± 3 meV GPa −1 , α 210K,170K = −48 ± 3 meV GPa −1 , α 120K,80K = −90 ± 3 meV GPa −1 . The pressure coefficient calculated theoretically within the DFT calculations at zero temperature is −100 ± 2 meV GPa −1 . The increasingly negative α values observed with decreasing temperature reflect the suppression of inorganic cage phonon activity and the reduced orientational freedom of MA + cations. These findings highlight the crucial influence of molecular dynamics and the interplay between organic and inorganic sublattices in governing the pressure response of hybrid perovskites across different structural phases.