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.