Neutron Diffraction and X-ray Absorption Fine Structure Evidence for Local Lattice Distortions and Aperiodic Antisite Substitution in Cu2ZnSnS4 Nanoparticles
Neutron Diffraction and X-ray Absorption Fine Structure Evidence for Local Lattice Distortions and Aperiodic Antisite Substitution in Cu2ZnSnS4 Nanoparticles
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DOI：
10.1021/jp502150s
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发表时间：
2014-11-13
影响因子：
3.7
通讯作者：
Conradson, Steven D.
中科院分区：
文献类型：
--
作者：
Espinosa-Faller, Francisco J.;Conradson, Dylan R.;Conradson, Steven D.
对Cu2ZnSnS4纳米颗粒（一种流行的光伏材料）进行了彻底的结构测定，使用中子衍射来表征长程平均晶体结构，使用X射线吸收精细结构（XAFS）光谱在Cu、Zn和Sn的K边来阐明元素特定的局部结构。这是第一个针对该材料纳米颗粒的组合多尺度方法。结果表明，存在的非周期性障碍的阳离子网站，减少退火。这种无序涉及晶体学位点周围的局部晶格畸变，而不是间隙原子的存在。这与已知的反位取代是CZTS的组成部分（指Cu，Zn和Sn在平面之间的排序）最一致。然而，取代无序不是被限制在单个晶胞内以保持晶体学对称性、周期性和均匀性，而是出现在由多个晶胞组成的更大区域上延伸，但仍然小于纳米颗粒的物理尺寸。因此，这些结果意味着存在纳米级域，其特征在于局部波动的组合物，导致个别域富集在某些金属离子和耗尽在其他。这些将通过在晶体中的其他位置处具有相反波动的域来反映，使得总体组成保持接近化学计量的Cu2ZnSnS4。由于相对低温的反应（300摄氏度）和退火（350摄氏度）条件，这种无序在这些样品中可能是明显的，并且可以预期对材料的所得物理性质及其光伏性能具有显著影响。
A thorough structure determination has been performed on Cu2ZnSnS4 nanoparticles, a popular photovoltaic material, using neutron diffractionto characterize the long-range average crystal structureand X-ray absorption fine structure (XAFS) spectroscopy at the Cu, Zn, and Sn K-edges to elucidate the element-specific local structure. This is the first combined multiscale approach on nanoparticles of this material. The results indicate the presence of aperiodic disorder on the cation sites that is diminished by annealing. This disorder involves local lattice distortions around the crystallographic sites rather than the presence of interstitial atoms. It is most consistent with the known antisite substitutions that are integral to CZTS (referring to the ordering of the Cu, Zn, and Sn between planes). However, instead of being confined within single unit cells so as to maintain the crystallographic symmetry, periodicity, and homogeneity, the substitutional disorder appears to extend over larger regions consisting of multiple unit cells but still smaller than the physical dimensions of the nanoparticles. These results therefore imply the presence of nanoscale domains characterized by local fluctuations in composition that cause the individual domains to be enriched in certain metal ions and depleted in others. These will be mirrored by domains with the opposite fluctuations at other locations in the crystal so that the overall composition remains close to the stoichiometric Cu2ZnSnS4. This disorder is likely pronounced in these samples due to the relatively low temperature reaction (300 degrees C) and annealing (350 degrees C) conditions and can be expected to have a significant effect on the resulting physical properties of the material and its photovoltaic performance.