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Insights into Twinning Formation in Cubic and Tetragonal Multi-cation Mixed-Halide Perovskite
Version 2 2020-03-18, 18:36
Version 1 2020-03-16, 15:32
journal contribution
posted on 2020-03-18, 18:36 authored by Huyen T. Pham, The Duong, Klaus J. Weber, Jennifer Wong-LeungWe
use a combination of low-dose electron microscopy studies and
atomic structure simulations to identify a common twinning structure
in both cubic and tetragonal phases of the multi-cation mixed-halide
perovskite. For the first time, we present clear evidence of {111}
twins in the cubic phase and the equivalent {011} twins in the tetragonal
phase using selected area electron diffraction (SAED) patterns. We
develop a unique way of differentiating between the tetragonal and
cubic forms of these twins. Our systematic electron diffraction analyses
and simulations demonstrate unequivocally that the same twinning structure
is present in both phases, notably with a perfectly coherent {111}
twin boundary in the cubic phase and a semi-coherent {011} twin boundary
in the tetragonal phase. The atomic configuration of the twin boundary
is discussed with possibilities of being AX3 centered (with
A = Cs, FA, MA and X = I, Br) or B-site centered (Pb) for both crystal
structures. We propose that the twin boundary is a key nucleation
region for phase segregation, which acts as a potential well or barrier
to electrons and holes depending on its composition and hence bandgap.