Calderón Ortiz Gabriel A, Zhu Menglin, Wadsworth Andrew, Dou Letian, McCulloch Iain, Hwang Jinwoo
Department of Materials Science and Engineering, The Ohio State University, Columbus, Ohio 43212, United States.
Department of Chemistry, Oxford University, Chemistry Research Laboratory, 12 Mansfield Road, Oxford OX1 3TA, U.K.
ACS Appl Mater Interfaces. 2024 Oct 4. doi: 10.1021/acsami.4c11198.
We present four-dimensional (4D) scanning transmission electron microscopy (STEM) analysis to obtain a high level of detail regarding the nanoscale ordering within largely disordered organic semiconducting polymers. Understanding nanoscale molecular ordering in semiconducting polymers is crucial due to its connection to the materials' important properties. However, acquiring such information in a spatially localized manner has been limited by the lack of a nanoscale experimental probe, weak signal from ordering, and radiation damage to the sample. By collecting nanodiffraction patterns with a high dynamic range pixelated detector, we acquired statistically robust, high signal-to-noise ratio diffraction patterns from semiconducting organic materials, including poly(3-hexylthiophene-2,5-diyl) (P3HT), P3HT/[6,6]-phenyl C61 butyric acid methyl ester, and indacenodithiophene--benzothiadiazole (IDTBT), which largely have disordered structures. Real-space images of the ordered domains were reconstructed from the 4D-STEM data set for a variety of scattering vectors and in-plane angles to capture the different molecular stacking distances and their in-plane orientation. These were then analyzed to obtain the average size of the ordered domains within the sample. Such measurements were arranged in a two-dimensional (2D) histogram, which showed a direct relationship between the type and size of molecular ordering. Complementary analyses, such as intensity variance and angular correlation, were applied to obtain ordering and symmetry information. These analyses enabled us to directly characterize the alkyl and π-π stacking of P3HT, as well as the fullerene domains caused by donor segregation in the P3HT sample. Furthermore, the analysis also captured changes in the P3HT domains when the fullerenes are incorporated. Lastly, IDTBT showed a much lesser degree of ordering without much disinclination between the domains within the 2D histogram. The 4D-STEM analysis that we report here unveils new details of molecular ordering that can be used to optimize the properties of this important class of materials.
我们展示了四维（4D）扫描透射电子显微镜（STEM）分析，以获取有关大部分无序的有机半导体聚合物内纳米级有序排列的高度详细信息。了解半导体聚合物中的纳米级分子排列至关重要，因为它与材料的重要特性相关。然而，以空间局部化的方式获取此类信息受到缺乏纳米级实验探针、有序排列信号微弱以及样品辐射损伤的限制。通过使用具有高动态范围像素化探测器收集纳米衍射图案，我们从包括聚（3-己基噻吩-2,5-二基）（P3HT）、P3HT/[6,6]-苯基C61丁酸甲酯和茚并二噻吩-苯并噻二唑（IDTBT）在内的半导体有机材料中获得了统计上可靠、高信噪比的衍射图案，这些材料大多具有无序结构。从4D-STEM数据集中重建了有序域的实空间图像，用于各种散射矢量和面内角度，以捕获不同的分子堆积距离及其面内取向。然后对这些进行分析，以获得样品内有序域的平均尺寸。此类测量结果排列在二维（2D）直方图中，该直方图显示了分子排列类型与尺寸之间的直接关系。应用了诸如强度方差和角度相关性等补充分析，以获取排列和对称性信息。这些分析使我们能够直接表征P3HT的烷基和π-π堆积，以及P3HT样品中由于供体分离引起的富勒烯域。此外，该分析还捕获了掺入富勒烯时P3HT域的变化。最后，IDTBT在2D直方图中的排列程度要低得多，且域之间的倾斜度不大。我们在此报告的4D-STEM分析揭示了分子排列的新细节，可用于优化这类重要材料的性能。
