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（OSCs）的最新进展是由非富勒烯受体（nfa）的发展所推动的，这已经改变了该领域的游戏规则。重要的是，基于nfa的OSCs似乎需要更小的驱动力才能有效地产生电荷，同时具有更小的开路电压损失。这就提出了一个问题，即是否类似于富勒烯太阳能电池中的机制决定了基于NFA的设备的效率，以及在适当设计NFA后，零驱动力的高效osc是否可行。本研究将探讨界面激发态（IFS）（通常称为CT态）的量子特性在电荷的产生、分离和重组中的作用。为此，我们将时间分辨光致发光，飞秒瞬态吸收光谱，温度和场相关的时间延迟收集场和准稳态光诱导吸收光谱应用于聚合物：NFA供体-受体系统，我们在60 meV的步骤中微调聚合物的HOMO。通过从具有突然界面的双层到优化的体异质结和最后的稀释混合物，我们将研究IFS直接环境系统变化的样品。我们的瞬态和稳态技术的独特结合，以及计算模型，将提供详细的见解，以确定这些能量和形态明确定义的样品中IFS的形成、解离、重组和衰变的速率。通过明确量子特性在关键光伏过程中的作用，我们旨在开发以最小能量抵消实现高效有机太阳能电池的策略。

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.