Pressure-Driven Helium Insertion for Structural Stability of CH₃NH₃PbBr₃ Hybrid Perovskites

Organic-inorganic metal halide perovskites (MHPs) have garnered significant attention due to their outstanding performance in optoelectronic devices, but they are prone to degradation through a variety of pathways. High-pressure studies are being used to understand the mechanical and structural stability of MHPs and investigate new methods for improving these. In this study, we map the high-pressure, low-temperature structural phase diagram of CH₃NH₃PbBr₃ (MAPbBr₃) between 15-300 K and up to 1.5 GPa. We first compare the temperature and pressure effects on the global and local structures of MAPbBr₃ using synchrotron X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS), respectively, and find evidence of PbBr₆ octahedral distortion. Our results also suggest that He inserts into the MAPbBr₃ structure. The thermodynamics of He insertion into MAPBHe _x are calculated to be plausible at room temperature for x ≤ 1 and P = 1-3 GPa and shown to stabilize higher-symmetry phases. This phenomenon increases the fitted bulk modulus of MAPbBr₃. Structural stabilization by inert atom insertion is proposed as a method to improve the mechanical robustness of MHPs and other soft hybrid materials.