posted on 2022-01-13, 10:43authored byGabriel
C. Halford, Qingmu Deng, Annie Gomez, Tianna Green, Jill M. Mankoff, Rebecca A. Belisle
Despite substantial research effort,
photoinduced halide segregation
in mixed halide perovskites continues to limit the available perovskite
chemistries for use in optoelectronic applications. In this study,
we present new insights into halide-segregation process through in
situ X-ray diffraction measurements that reveal substantial structural
changes in mixed-halide perovskites under excitation. We observe that
photoinduced halide segregation leads to the formation of one iodide-rich
and one bromide-rich perovskite composition whose Br:I ratios are
the same (at 20 and 93% bromine, respectively), for a range of compositions
of the pristine initial perovskite phase. This segregation reverses
in the dark to re-form a mixed halide perovskite with the same lattice
spacing as the pristine perovskite. From these results, we determine
a kinetic rate for the formation and dissolution of these new crystalline
phases and observe that the crystalline orientation is preserved through
the light-segregation and dark-relaxation processes. Our results are
consistent with a model of halide segregation where excitation causes
changes in the free energy of mixing and ultimately the formation
of a miscibility gap in the MAPb(IxBr1–x)3 phase diagram and
should inform future works to model and manipulate the halide-segregation
process in mixed-halide perovskites.