Microscopic picture of charge generation in conjugated polymers

半导体共轭聚合物是一类新兴的材料，在光电子学、光子学和光伏学等领域有着广阔的应用前景。在本项目中，我们将从微观理论的角度研究共轭聚合物中的电荷产生。这包括(i)通过分子掺杂产生电荷的研究，这对光电应用很重要，以及（ii）光激发后产生电荷的研究，这是有机光伏的核心过程。我们的研究将集中在技术相关的共聚物与内置供体-受体结构。这些共聚物的好处（除其他外）在于电荷分离效率的提高。另一方面，最近发现，在这些更复杂的体系中，掺杂效率受到用于掺杂的小分子相对于共轭链随机定位的几何无序的影响。在本项目的第一部分，我们将回顾不同的电子机制，如电荷转移络合物的形成和整数电子转移有助于共轭聚合物掺杂。我们将对起作用的物理/化学过程进行详细的微观理解，从长远来看，这将使我们能够制定更有效的掺杂策略。本项目将探索的一个可能的途径是使用足够大的掺杂剂分子来插入共轭链的供体和受体实体之间。本项目的第二部分将关注通过共轭链中的主要光诱导激发（激子）解离成分离或松散结合的电荷载流子来产生电荷。基于光激发后激发态流形中非绝热分子动力学的从头计算，我们将直接分析过量激发能对解离过程的影响，并明确研究分子内和分子间弛豫通道的作用。本项目的一个重要组成部分也是我们与实验伙伴的合作。电子激发和振动模式的光谱学将揭示相关电子机制的特征指纹，并将直接与理论获得的光谱性质相比较。基于本项目将研究的潜在基本物理过程，将得出适用于大类共轭材料的一般结论，并将有助于提高这些材料在未来的性能潜力。

Semiconducting conjugated polymers are an emerging class of materials that bear great promise for various applications in optoelectronics, photonics, and photovoltaics. In the present project, we will study charge generation in conjugated polymers from a microscopic theoretical perspective. This includes both studies of (i) charge generation through molecular doping, important for optoelectronic applications, and (ii) charge photo-generation after optical excitation, the process at the heart of organic photovoltaics. Our study will be focussed on technologically relevant co-polymers with built-in donor-acceptor structure. The benefits of these co-polymers lie (among other things) in an increased charge separation efficiency. On the other hand, it was recently found that the doping efficiency in these more complex systems is affected by geometrical disorder in the random positioning of the small molecules used for doping relative to the conjugated chains. In the first part of the present project, we will revisit the different electronic mechanisms such as charge-transfer complex formation and integer electron transfer contributing to doping of conjugated polymers. We will develop a detailed microscopic understanding of the physical/chemical processes at work which in the long run will allow us to develop strategies to achieve more efficient doping. A possible route that will be explored in the present project is the use of dopant molecules that are large enough to interpolate between donor and acceptor entities of the conjugated chains. The second part of the present project will be concerned with charge generation through dissociation of the primary photo-induced excitations (excitons) in conjugated chains into separated or loosely bound charge carriers. Based on ab-initio calculations of the non-adiabatic molecular dynamics in the excited-state manifold after photo-exitation, we will directly analyze the influence of excess excitation energy on dissociation processes and explicitly study the role of intra- and inter-molecular relaxation channels. An important ingredient to the present project also is our work together with our experimental partners. Optical spectroscopy of electronic excitations and vibrational modes will reveal characteristic fingerprints of the relevant electronic mechanisms and will be directly comparable to the spectral properties obtained theoretically. Based on the underlying fundamental physical processes that will be studied in the present project, general conclusions will be drawn that are applicable to a large class of conjugated materials and will contribute to improving performance potential of these materials in the future.