期刊
CHEMPHYSCHEM
卷 16, 期 14, 页码 3064-3071出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/cphc.201500374
关键词
crystal growth; X-ray diffraction; electron microscopy; perovskite phases; solid-state structures
资金
- CNR Italian project EFOR-CABIR [CUP B51J10001290001]
- Grants-in-Aid for Scientific Research [26289265] Funding Source: KAKEN
We investigate the degradation path of MAPbI(3) (MA=methylammonium) films over flat TiO2 substrates at room temperature by means of X-ray diffraction, spectroscopic ellipsometry, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. The degradation dynamics is found to be similar in air and under vacuum conditions, which leads to the conclusion that the occurrence of intrinsic thermodynamic mechanisms is not necessarily linked to humidity. The process has an early stage, which drives the starting tetragonal lattice in the direction of a cubic atomic arrangement. This early stage is followed by a phase change towards PbI2. We describe how this degradation product is structurally coupled with the original MAPbI(3) lattice through the orientation of its constituent PbI6 octahedra. Our results suggest a slight octahedral rearrangement after volatilization of HI+CH3NH2 or MAI, with a relatively low energy cost. Our experiments also clarify why reducing the interfaces and internal defects in the perovskite lattice enhances the stability of the material.
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