Interplay between microscopic structure and intermolecular charge transfer processes in polymer-fullerene bulk-heterojunctions

在这个后续项目中，我们计划对聚合物半导体及其与电子受体部分的混合物中的电荷转移(CT)过程进行系统的研究。我们的研究目的是在微观水平上阐明CT和胶片形态之间的关系。在第一个应用阶段，我们开发了一套独特的工具来研究纳米尺度的薄膜结构以及有机体异质结太阳能电池中的激发态。我们实施并应用了光学探测磁共振装置，发现了与区域规则聚己基噻吩三重态激子的形成有关的惊人结果。三重态激子通常被认为是有机光伏中的损耗因子。我们确定了这些三重态的空间范围，范围从几个？ngstroms(分子三重激子)到几个纳米。后者我们用CT激子或极化子对识别有机太阳能电池中自由电荷的前驱状态--因此对它们的性能至关重要。不同的三重态取决于薄膜的形貌，我们用基于扫描力显微镜(SFM)的纳米层析成像技术对其进行了研究。通过开发合适的等离子体刻蚀配方，SFM纳米层析首次适用于研究共轭聚合物和施主-受主共混物。到目前为止，我们展示了P3HT：PCBM混合物的10 nm分辨率的3D体积成像。虽然第一个提议阶段的结果是新颖和有趣的，但三重态的微观性质仍然没有解决。

In this follow-up project we plan to perform systematic studies of charge transfer (CT) processes in polymer semiconductors and their blends with electron acceptor moieties. Our investigations are aimed at clarifying the correlation between CT and film morphology on the microscopic level. In the first application period, we developed a unique set of tools to study film structure on the nanometer scale as well as excited states in organic bulk heterojunction solar cells. We implemented and applied an optically detected magnetic resonance setup, and found surprising results related to formation of triplet excitons with different spatial extent in the conjugated polymer rr-P3HT (regio-regular poly-hexylthiophene). Triplet excitons are generally considered as loss factors in organic photovoltaics. We determined spatial extents of these triplet states ranging from few Ångstroms (molecular triplet excitons) to several nanometers. The latter we identify with CT excitons, or polaron pairs, the precursor state of free charges in organic solar cells—and thus crucial for their performance. The different triplet states occur depending on the film morphology, which we studied by scanning force microscopy (SFM) based nanotomography. SFM-nanotomography was for the first time adapted to study conjugated polymers and donor-acceptor blends by development of a suitable plasma-etching recipe. So far we demonstrated 3D volume imaging with 10 nm resolution of a P3HT:PCBM blend. Although the results of the first proposal period are novel and interesting, the microscopic nature of the triplet states remains unresolved.