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Insights into Twinning Formation in Cubic and Tetragonal Multi-cation Mixed-Halide Perovskite
ACS Materials Letters ( IF 11.4 ) Pub Date : 2020-03-11 , DOI: 10.1021/acsmaterialslett.0c00083
Huyen T. Pham 1 , The Duong 2 , Klaus J. Weber 2 , Jennifer Wong-Leung 1
Affiliation  

We 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.

中文翻译:

立方和四方多阳离子混合卤化物钙钛矿中孪晶形成的见解

我们结合使用低剂量电子显微镜研究和原子结构模拟来确定多阳离子混合卤化物钙钛矿的立方相和四方相中的常见孪生结构。首次,我们使用选定的区域电子衍射(SAED)模式提供了立方相中{111}孪晶和四方相中等效的{011}孪晶的清晰证据。我们开发出一种区分这些双胞胎的四边形和立方形的独特方法。我们系统的电子衍射分析和模拟明确表明,在两个相中都存在相同的孪生结构,特别是在立方相中具有完美相干的{111}双晶界,在四方相中具有半相干的{011}双晶界。两个晶体结构的3个居中(A = Cs,FA,MA和X = I,Br)或B位居中(Pb)。我们提出,孪晶边界是相分离的关键成核区域,它根据其组成以及带隙而充当电子和空穴的势阱或势垒。
更新日期:2020-04-23
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