Photo-induced Macro/Mesoscopic Scale Ion Segregation in Mixed-Halide Perovskites: Ring Structure and Ionic Plasma Oscillations

TL;DR

This study reveals that light-induced halide ion segregation in mixed-halide perovskites results in macro/mesoscopic ring structures due to ion diffusion and Coulombic forces, and demonstrates ionic plasma oscillations upon light removal.

Contribution

It uncovers the counterintuitive ion diffusion mechanism and reports the first observation of ionic plasma oscillations in solid-state perovskites.

Findings

Formation of photoluminescence rings due to ion diffusion

Observation of ultra-low-frequency ionic plasma oscillations

Reversible ion redistribution upon illumination removal

Abstract

Contrary to the common belief that light-induced halide ion segregation in a mixed halide al-loy occurs within the illuminated area, we find that the Br ions released by light diffuse away from the area, which generates a counter-balancing Coulombic force between the anion deficit and surplus region, together resulting in a macro/mesoscopic size anion ring surrounding the center, showing a photoluminescence ring. Upon removing the illumination, the displaced anions return to the illuminated area, and the restoring force leads to a damped ultra-low-frequency oscillatory ion motion, which may be the first observation of an ionic plasma oscillation in solids.