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

在这个后续项目中，我们计划进行系统的研究电荷转移（CT）过程中的聚合物半导体和它们的共混物与电子受体部分。我们的调查旨在澄清CT和电影形态之间的相关性在微观层面上。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上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检测的磁共振装置，并发现了与在共轭聚合物rr-P3 HT（区域规则的聚己基噻吩）中形成具有不同空间范围的三重态激子相关的令人惊讶的结果。三重态激子通常被认为是有机光致发光中的损耗因子。我们确定了这些三重态的空间范围从几纳米（分子三重态激子）到几纳米。后者我们认为是CT激子，或者极化子对，有机太阳能电池中自由电荷的前体状态，因此对它们的性能至关重要。不同的三重态发生依赖于薄膜的形态，我们研究了基于扫描力显微镜（SFM）的纳米断层扫描。SFM-纳米断层扫描是第一次适应研究共轭聚合物和供体-受体共混物通过开发一个合适的等离子体蚀刻配方。到目前为止，我们展示了具有10 nm分辨率的P3 HT：PCBM混合物的3D体积成像。虽然第一个提案期的结果是新颖和有趣的，三重态的微观性质仍然没有得到解决。

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.