Visualizing Phase Segregation in Mixed‐Halide Perovskite Single Crystals

Iodide‐rich clusters form and grow in the MAPb(Br_x I_1−x )₃ single crystal under continuous light illumination. A combination of widefield microscopy and confocal microscopy provides detailed insight into phase segregation in individual MAPb(Br_x I_1−x )₃ microplatelets.

Abstract

Mixed organolead halide perovskites (MOHPs), CH₃NH₃Pb(Br_x I_1−x )₃, have been shown to undergo phase segregation into iodide‐rich domains under illumination, which presents a major challenge to their development for photovoltaic and light‐emitting devices. Recent work suggested that phase‐segregated domains are localized at crystal boundaries, driving investigations into the role of edge structure and the growth of larger crystals with reduced surface area. Herein, a method for growing large (30×30×1 μm³) monocrystalline MAPb(Br_x I_1−x )₃ single crystals is presented. The direct visualization of the growth of nanocluster‐like I‐rich domains throughout the entire crystal revealed that grain boundaries are not required for this transformation. Narrowband fluorescence imaging and time‐resolved spectroscopy provided new insight into the nature of the phase‐segregated domains and the collective impact on the optoelectronic properties.

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