The pressure and temperature dependence of the local and long-range structure of CH₃NH₃PbBr₃

Organic-inorganic metal halide perovskites (MHPs) have garnered significant attention due to their outstanding optoelectronic properties, including high absorption coefficients, long carrier diffusion lengths, and tunable bandgaps. Recent advances have pushed perovskite solar cell efficiencies to 26.4%. However, long-term stability remains a major challenge. MHPs are highly sensitive to environmental stressors, with materials such as methylammonium lead bromide (CH₃NH₃PbBr₃) exhibiting structural and chemical degradation under humidity, thermal cycling, and mechanical stress. These degradation mechanisms compromise device performance over time and present critical barriers to the scalability and reliability of perovskite-based technologies. In this study, we map the high-pressure and low-temperature structural phase diagram of CH₃NH₃PbBr₃ between 15 K and room temperature and up to 1.5 GPa. We investigate how temperature and pressure influence the local structure of MHPs using extended X-ray absorption fine structure (EXAFS) and X-ray diffraction (XRD) to quantify both static and dynamic disorder. Our results also provide experimental and theoretical evidence for helium diffusion within the lattice, a phenomenon that prevents amorphization and offers a potential strategy for designing hybrid perovskites with enhanced stability. This work represents a systematic study of the pressure dependence of disorder in hybrid-lead halide perovskites (LHPs), offering new insights into halide migration and lattice behavior under extreme conditions.