单线态裂分聚合物材料及其光伏体系中光电转换过程的超快动力学研究

The singlet exciton formed in the case of photoexcitaion of some conjugated organic moelucules can be converted into two triplet excitons by singlet fission (SF). The photon-to-electricity conversion efficiency (PCE) of the photovoltaics can be significantly boosted, provided that the triplet excitons by SF could further dissociate into free charges. At present, improving the PCE by making use of polymeric materials with SF effect has attracted intensive interests. Under the background of the exploration of SF materials and their application in photovoltaics, this project concentrates on studying the formation process of triplet exciton by SF and the entire pathway for triplet excitons to free charges on long timescales from femtosecond to microsecond via ultrafast spectroscopy combined with theoretical computation and dynamic simulation. In addition, by modulating the molecular structure and microstructure of SF materials, the key factors in structure and dynamics for affecting SF process and further the triplet exciton dissociating into free charge, are on the point of being explored. Taken together, this project will enhance the understanding of the structure-function relationship of SF materials applied in photovoltaics, and will provide guidelines and strategies to further increase the PCE of organic solar cells.

光激发某些共轭有机分子体系形成的单线态激子能够通过单线态裂分（SF）反应转化为两个三线态激子；SF产生的三线态激子若进一步解离为自由电荷，则可大幅提高光电转换效率（PCE）。目前，通过利用具有SF效应的聚合物材料来提高有机太阳能电池的PCE是光伏研究的前沿和热点领域。在SF材料探索及其在光伏体系中应用的背景下，本项目拟通过超快光谱学手段并结合理论计算与动力学模拟，从飞秒-微秒时间尺度上研究SF产生三线态激子、以及三线态激子向自由电荷转化的全过程，结合对SF材料的分子结构和纳微结构的调控，探究影响SF反应和三线态激子解离的关键结构和动力学因素。本项目的研究成果将加深对SF材料光伏应用构效关系的规律性认识，为进一步提高有机太阳能电池光电转换效率提供理论依据和新思路。

单线态裂分是激发态弛豫中非常重要的一个衰减途径。我们通过超快光谱揭示了杂原子的变化不仅影响其单线态向三线态系间窜越的时间常数，还会导致在超快时间内（亚皮秒到皮秒量级）生成的三线态逐渐增加，该过程指认为单线态裂分生成三线态的过程，表明了杂原子在分子内单线态裂分过程中所起的作用，进一步验证了单线态裂分和系间窜越是三线态的两个重要来源。只有了解了系间窜越的影响因素和结构因素，才有利于针对性的抑制单线态系间窜越生成三线态，避免在利用单线态裂分的过程中相互竞争而引起单线态裂分量子产率降低。此外，揭示了溶剂可以调控其激发态动力学行为，发光过程与单线态裂分过程相竞争，该现象为针对性的调控发光分子的激发态行为提供了理论依据。此外，还在一定程度上揭示了氢键在分子内单线态裂分过程中所起的作用。