Effective Suppressing Phase Segregation of Mixed‐Halide Perovskite by Glassy Metal‐Organic Frameworks

Abstract Lead mixed‐halide perovskites offer tunable bandgaps for optoelectronic applications, but illumination‐induced phase segregation can quickly lead to changes in their crystal structure, bandgaps, and optoelectronic properties, especially for the Br–I mixed system because CsPbI3 tends to form a non‐perovskite phase under ambient conditions. These behaviors can impact their performance in practical applications. By embedding such mixed‐halide perovskites in a glassy metal‐organic framework, a family of stable nanocomposites with tunable emission is created. Combining cathodoluminescence with elemental mapping under a transmission electron microscope, this research identifies a direct relationship between the halide composition and emission energy at the nanoscale. The composite effectively inhibits halide ion migration, and consequently, phase segregation even under high‐energy illumination. The detailed mechanism, studied using a combination of spectroscopic characterizations and theoretical modeling, shows that the interfacial binding, instead of the nanoconfinement effect, is the main contributor to the inhibition of phase segregation. These findings pave the way to suppress the phase segregation in mixed‐halide perovskites toward stable and high‐performance optoelectronics.