Exploring the Quantum Character of Interfacial Excitations at the Donor-Acceptor Heterojunction – Towards Efficient Organic Solar Cells with Minimum Energy Offset

有机太阳能电池（OSC）的最新进展，由非富勒烯受体（NFA）的最新发展所实现，已经成为该领域的游戏规则改变者。重要的是，基于NFA的OSC似乎需要更小的驱动力来产生电荷以有效地工作，具有更小的开路电压损耗的好处。这就提出了一个问题，即与富勒烯基太阳能电池类似的机制是否决定了NFA基器件的效率，以及具有零驱动力的高效OSC是否可以在NFA的适当设计后变得可行。本研究将探讨界面激发态（IFS）（通常称为CT态）的量子特性在电荷产生、分离和复合中的作用。为此，我们应用时间分辨光致发光，飞秒瞬态吸收光谱，温度和场依赖的时间延迟收集场和准稳态光诱导吸收光谱的聚合物：NFA供体-受体系统，我们微调的HOMO的聚合物的步骤为60毫电子伏。通过移动从双层突然的界面，优化散装异质结，最后稀释共混物，我们将调查样品的IFS的直接环境是系统地变化。我们的瞬态和稳态技术的独特组合，沿着与计算建模，将提供详细的洞察力的过程中确定的形成，解离，重组和衰减的IFS在这些精力充沛和形态定义良好的样品。通过阐明量子特性在关键光伏过程中的作用，我们的目标是开发策略，以实现具有最小能量偏移的高效有机太阳能电池。

Recent advances in organic solar cells (OSCs), enabled by the recent development of non-fullerene acceptors (NFAs) have been a game changer in the field. Importantly, NFA-based OSCs seem to require a smaller driving force for charge generation to work efficiently, with the benefit of a smaller open circuit voltage loss. This raises the question whether or not similar mechanisms as in fullerene-based solar cells dictate the efficiency of NFA-based devices and whether efficient OSCs with zero driving force may become feasible upon proper design of the NFA. This research will investigate the role of the quantum characteristics of the interfacial excited state (IFS), commonly called CT state, in the generation, separation and recombination of charges. To this end, we apply time resolved photoluminescence, femtosecond transient absorption spectroscopy, temperature and field dependent time delayed collection field and quasi-steady-state photoinduced absorption spectroscopy to polymer:NFA donor-acceptor systems where we fine-tune the HOMO of the polymer in steps of 60 meV. By moving from bilayers with abrupt interface to optimized bulk heterojunctions and finally dilute blends, we will investigate samples where the direct environment of the IFS is systematically varied. The unique combination of our transient and steady-state techniques, along with computational modelling, will provide detailed insight into the processes determining the rate of the formation, dissociation, reformation and decay of the IFS in these energetically and morphologically well-defined samples. By clarifying the role of the quantum characteristics in key photovoltaic processes, we aim at developing strategies to realize efficient organic solar cells with minimum energy offset.