Optical Properties of Ion Accumulation Areas in MAPbX₃ Single Crystals

Hybrid organic–inorganic perovskite (HOIP) material‐based devices have attracted much attention in the past few years owing to their superior photoelectric performance. However, ion migration has hindered the commercialization of these devices. The accumulation of migrated ions or defects near electrodes and boundaries is inevitable under a voltage bias. This paper reports a systematic study on the optical properties of ion accumulation areas in HOIP. Quantitative electric fields are applied to MAPbX 3 (MA = methylammonium and X = Cl, Br, or I) single crystals, and micro‐optical characterizations, including photoluminescence (PL) spectra, PL lifetimes, and Raman spectra, are performed. Significant differences in the intensity and peak position are observed in the PL spectrum near the anode and cathode regions, respectively. The phenomena observed in the study can be attributed to the migration and accumulation of halide ions, halide vacancies, and MA + ions. Moreover, the results reveal that halide ions and vacancies play a significant role in carrier recombination. Finally, the Raman spectrum confirms that the migrated ions affect the interaction between the organic MA + ions and inorganic Pb–X cages.