超快光谱研究有机非富勒烯太阳能电池的载流子动力学

Bulk-heterojunction organic solar cells (BHJ-OSCs) have been dominated by donor:acceptor blends based on fullerene acceptors for over two decades. Recently, non-fullerene (NF) OSCs, with easily modified chemical structure and highly adjustable physical properties, have been developed very quickly. The power conversion efficiencies of NF OSCs have now reached a value of over 14%, which is higher than the best fullerene-based OSCs. Compared with fullerene-based OSCs, the most striking feature of NF-based OSCs is that a wide range of devices show efficient charge generation upon small (even negligible) driving energies. At this stage, it’s not clear whether similar or different mechanisms are contributing to the charge separation process in NF OSCs. Therefore, in this project, we employ broadband femtosecond time-resolved transient absorption spectroscopy and transient absorption microscopy, to explore how the blend morphology/structure and energetics influence the charge separation and recombination dynamics. The relationship between active layer structure, excitation state dynamics and device performance will be established to ultimately promote the design of NF OSCs photovoltaic materials and the improvement of device performance.

20多年来，有机太阳能电池活性层一直以基于富勒烯受体的供体-受体共混的体异质结为主。然而最近，非富勒烯受体由于易于修饰的化学结构和高度可调的物理性质，获得了迅速发展，得到了比富勒烯体系更高的太阳能转化效率14%。与富勒烯太阳能电池相比，非富勒烯器件最显著的特点是在很小（甚至可以忽略不计）的驱动能量下高效的产生电荷，有机非富勒烯太阳能电池中电荷分离过程的机制是否和富勒烯体系相同，目前还没有明确的理论解释。为此，本项目将利用宽带飞秒时间分辨瞬态吸收光谱技术以及瞬态吸收显微镜技术，探讨有机非富勒烯异质结的活性层形貌/结构以及能级分布对电荷分离和复合过程的动力学的影响。建立活性层结构、激发态动力学和器件性能之间的联系，最终推动非富勒烯光伏材料的设计发展和器件性能的提高。

近年来，非富勒烯受体材料由于易于修饰的化学结构和高度可调的物理性质，获得了迅速发展。然而目前，器件物理研究却滞后于材料的快速发展。本项目利用飞秒瞬态吸收光谱技术，对比研究了系列端基共轭长度不同的非富勒烯小分子的载流子动力学。通过超快光谱和理论计算，发现大pi共轭的端基结构更有助于形成高度有序的分子堆积形貌，实现有效的电荷分离。非富勒烯受体小分子的端基共轭长度对其器件的光电性能起着关键作用。此外分析了CsPbI3薄膜形貌改变对其载流子动力学的作用机制，以及芘核树枝状分子的离域激发和分子内能量转移过程，为新型光电器件的发展提供了理论基础。在本项目的支持下，发表sci论文3篇（已标注），正在整理研究结果1篇。