Patil Nilesh, Skjønsfjell Eirik Torbjørn Bakken, Van den Brande Niko, Chavez Panduro Elvia Anabela, Claessens Raf, Guizar-Sicairos Manuel, Van Mele Bruno, Breiby Dag Werner
Department of Physics, Norwegian University of Science and Technology (NTNU), 7491, Trondheim, Norway.
Physical Chemistry and Polymer Science (FYSC), Vrije Universiteit Brussel, 1050, Brussels, Belgium.
PLoS One. 2016 Jul 1;11(7):e0158345. doi: 10.1371/journal.pone.0158345. eCollection 2016.
Optimizing the morphology of bulk heterojunctions is known to significantly improve the photovoltaic performance of organic solar cells, but available quantitative imaging techniques are few and have severe limitations. We demonstrate X-ray ptychographic coherent diffractive imaging applied to all-organic blends. Specifically, the phase-separated morphology in bulk heterojunction photoactive layers for organic solar cells, prepared from a 50:50 blend of poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) and thermally treated for different annealing times is imaged to high resolution. Moreover, using a fast-scanning calorimetry chip setup, the nano-morphological changes caused by repeated thermal annealing applied to the same sample could be monitored. X-ray ptychography resolves to better than 100 nm the phase-segregated domains of electron donor and electron acceptor materials over a large field of view within the active layers. The quantitative phase contrast images further allow us to estimate the local volume fraction of PCBM across the photovoltaically active layers. The volume fraction gradient for different regions provides insight on the PCBM diffusion across the depletion zone surrounding PCBM aggregates. Phase contrast X-ray microscopy is under rapid development, and the results presented here are promising for future studies of organic-organic blends, also under in situ conditions, e.g., for monitoring the structural stability during UV-Vis irradiation.
众所周知，优化本体异质结的形态可显著提高有机太阳能电池的光伏性能，但现有的定量成像技术很少且有严重局限性。我们展示了应用于全有机共混物的X射线叠层相干衍射成像。具体而言，对由聚（3-己基噻吩）（P3HT）和苯基-C61-丁酸甲酯（PCBM）按50:50比例混合并经过不同退火时间热处理制备的有机太阳能电池本体异质结光活性层中的相分离形态进行了高分辨率成像。此外，使用快速扫描量热芯片装置，可以监测对同一样品进行重复热退火引起的纳米形态变化。X射线叠层成像在大视场内将有源层中电子供体和电子受体材料的相分离域分辨到优于100 nm。定量相衬图像进一步使我们能够估计整个光伏有源层中PCBM的局部体积分数。不同区域的体积分数梯度为PCBM在PCBM聚集体周围耗尽区的扩散提供了见解。相衬X射线显微镜正在迅速发展，这里展示的结果对于未来有机-有机共混物的研究很有前景，也适用于原位条件下的研究，例如用于监测紫外-可见光照期间的结构稳定性。
