直接电子探测和PCA对有机光致发光材料EELS研究的益处
Benefits of direct electron detection and PCA for EELS investigation of organic photovoltaics materials
摘要：
电子能量损失谱（EELS）是一种强大的工具，用于成像纳米尺度的化学变化。在这里，我们研究了聚合物/有机小分子共混物作为吸收层的有机太阳能电池和采用EELS区分聚合物供体和小分子受体域的纳米结构的共混物的基础上轻元素，如氮，硫或氟的元素地图。特别是对于束敏感样品，需要限制电子剂量，因此需要优化的采集和数据处理策略。我们比较后柱能量过滤器与直接电子探测相机从传统的CCD相机在同一过滤器上的数据采集的数据，我们调查的影响，统计数据处理方法（主成分分析，PCA）对采集的光谱和元素图从光谱图像中提取。我们的工作表明，直接电子探测相机上的光谱质量远远优于传统的CCD成像，从而可以清楚地识别电离边缘和这些边缘的精细结构。对于元素图的质量，PCA的应用是必不可少的，以允许在非富勒烯有机太阳能电池的本体异质结吸收层中的供体和受体相之间的清晰分离。
英文摘要：
Electron energy-loss spectroscopy (EELS) is a powerful tool for imaging chemical variations at the nanoscale. Here, we investigate a polymer/organic small molecule-blend used as absorber layer in an organic solar cell and employ EELS for distinguishing polymer donor and small molecule acceptor domains in the nanostructured blend based on elemental maps of light elements, such as nitrogen, sulfur or fluorine. Especially for beam sensitive samples, the electron dose needs to be limited, therefore optimized acquisition and data processing strategies are required. We compare data acquired on a post-column energy filter with a direct electron detection camera to data from a conventional CCD camera on the same filter and we investigate the impact of statistical data processing methods (principal components analysis, PCA) on acquired spectra and elemental maps extracted from spectrum images. Our work shows, that the quality of spectra on a direct electron detection camera is far superior to conventional CCD imaging, and thereby allows clear identification of ionization edges and the fine structure of these edges. For the quality of the elemental maps, the application of PCA is essential to allow a clear separation between the donor and acceptor phase in the bulk heterojunction absorber layer of a non-fullerene organic solar cell.
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