非富勒烯有机太阳能电池中激子在给受体界面分离过程的理论研究

Non-fullerene organic solar cells have reached excellent power conversion efficiencies, however, the mechanisms of exciton dissociation for donor (D) and acceptor (A) at the D/A interface are still not completely understood. Therefore, this project aims to study and unravel the exciton-dissociation processes in non-fullerene organic solar cells by means of quantum-chemical methods. For this purpose, we evaluate the relationship between interfacial excited-state energy difference and charge-transfer rate, electronic properties of the molecular local excited states and complex charge-transfer state, electronic couplings and reaction rates between the two kinds of excited states, and then investigate the impact of driving force on exciton dissociation, the pathways for exciton dissociation (especially hot exciton), and exciton delocalization properties. Also, we will deeply study the impact of relative orientations and positions between D and A, molecular stacking structures (mainly for acceptors) on exciton-dissociation processes. It is expected to provide guidlines for experiment to optimize molecular structure and further improve power conversion efficiency.

非富勒烯有机太阳能电池实现了优异的能量转换效率，但是激子在给受体界面的分离机制仍然还未完全理解。因此，本项目拟使用量子化学方法研究并揭示非富勒烯有机太阳能电池给体和受体激子的分离过程及机理。通过计算界面激发态能量差与电荷转移速率关系、分子局域激发态与复合物电荷转移态的电子性质以及它们之间的电子耦合和反应速率，研究驱动力对激子分离的影响、激子分离通道（特别是热激子分离过程）以及激子离域性质。本项目还将深入研究给受体分子间的相对位置和取向、分子堆积结构（主要是受体分子）对激子分离的影响，期望对实验上优化分子设计和进一步提高能量转换效率有指导意义。

尽管给受体界面空穴转移的驱动力非常小，非富勒烯有机光伏电池仍然实现了低的开路电压损失以及很高的能量转换效率。因此，深入理解界面激子分离和电荷复合过程对进一步提高光伏性能具有非常重要的意义。本项目以具有最高能量转换效率的D18/Y6复合物为研究对象，构建了一系列D18/Y6复合物界面结构，计算了所有结构激子分离和电荷复合过程的电子耦合、电荷转移速率等性质。计算结果表明，Y6激子只能通过最低电荷转移态发生分离，而D18激子还可以通过四个高能级的电荷转移态发生分离。同时，电荷复合速率比激子分离速率要低几个数量级。这些结果强调了多通道激子分离对高效率有机光伏的重要性。