Ravi Vikash Kumar, Santra Pralay K, Joshi Niharika, Chugh Jeetender, Singh Sachin Kumar, Rensmo Håkan, Ghosh Prasenjit, Nag Angshuman
Division of Molecular and Condensed Matter Physics, Department of Physics and Astronomy, Uppsala University , Box 516, 75120 Uppsala, Sweden.
J Phys Chem Lett. 2017 Oct 19;8(20):4988-4994. doi: 10.1021/acs.jpclett.7b02192. Epub 2017 Sep 29.
Optoelectronic properties of CsPbBr perovskite nanocubes (NCs) depend strongly on the interaction of the organic passivating molecules with the inorganic crystal. To understand this interaction, we employed a combination of synchrotron-based X-ray photoelectron spectroscopy (XPS), nuclear magnetic resonance (NMR) spectroscopy, and first-principles density functional theory (DFT)-based calculations. Variable energy XPS elucidated the internal structure of the inorganic part in a layer-by-layer fashion, whereas NMR characterized the organic ligands. Our experimental results confirm that oleylammonium ions act as capping ligands by substituting Cs ions from the surface of CsPbBr NCs. DFT calculations shows that the substitution mechanism does not require much energy for surface reconstruction and, in contrast, stabilizes the nanocrystal by the formation of three hydrogen bonds between the -NH moiety of oleylammonium and surrounding Br on the surface of NCs. This substitution mechanism and its origin are in stark contrast to the usual adsorption of organic ligands on the surface of typical NCs.
CsPbBr钙钛矿纳米立方体（NCs）的光电特性强烈依赖于有机钝化分子与无机晶体之间的相互作用。为了理解这种相互作用，我们采用了基于同步加速器的X射线光电子能谱（XPS）、核磁共振（NMR）光谱以及基于第一性原理密度泛函理论（DFT）的计算相结合的方法。可变能量XPS以逐层方式阐明了无机部分的内部结构，而NMR则对有机配体进行了表征。我们的实验结果证实，油胺离子通过从CsPbBr NCs表面取代Cs离子而充当封端配体。DFT计算表明，这种取代机制不需要太多能量进行表面重构，相反，通过在油胺的-NH部分与NCs表面周围的Br之间形成三个氢键使纳米晶体稳定。这种取代机制及其起源与典型NCs表面有机配体的通常吸附形成了鲜明对比。
