有机材料中热激子能量弛豫和解离的量子动力学理论

Organic solar cell is one of importantly potential clear energy sources, and its energy conversion efficiency is dominantly determined by the exciton dissociation and migration whose competing mechanism is not well understood yet. Recently, a hot exciton concept is experimentally proposed to further enhance the conversion efficiency. But, the different conclusions result in a bitter argument for the mechanism of exciton dissociation. This controversy also puts forward the new challenges for the theoretical description of exciton dynamics in both quantum dynamics and electronic structure methods because of too large organic polymers as well as their aggregates in the cell. The project will thus develop the corresponding quantum dynamic methods to illustrate the competing mechanism of hot exciton dissociation and migration, and related other dynamic processes. The project firstly proposes the quantum dynamic method which should uniformly describe the coherent and hopping motions of hot carriers in cell systems, and completely describe exciton dissociation and migration dynamics. Then, the project will focus on the energy relaxation dynamics of hot exciton to build the relationship between exciton dissociation and exciton initial condition generated by the laser with different frequencies and pulse durations, and to reveal the implicit mechanism of controversial experimental results. Finally, the project will efficiently connect the developed quantum dynamics and electronic structure methods to achieve the simulations for realistic organic solar cells, reveal their structure-function relationship, and propose the ways for designing efficient solar cells.

有机太阳能电池是很具潜力的新型清洁能源，其内的激子迁移和解离过程是提高转化效率的关键因素，但在理解其机理时存在诸多争议，尤其是最近在调查热激子影响转化效率的问题上，不同实验的矛盾结果产生了更广泛争论；由于缺乏有效理论模型和计算工具，理论化学在揭示其机理时也面临诸多挑战。项目拟发展创新性的量子动力学方法并结合电子结构计算从微观原子层面上来揭示热激子的产生、迁移及分离及其相关的动力学过程。首先，发展能够统一处理热激子相干、扩散和解离过程且适用于电池体系的量子动力学方法来阐明其迁移和解离的竞争机制；其次，深入研究热激子能量弛豫的动力学过程，并建立能量弛豫与激子解离的关系，调查产生热激子的激光中心频率和脉冲宽度对激子解离的影响，尝试阐明不同实验条件下得到矛盾结果的来源；最后，将发展的动力学方法与电子结构计算方法相结合，调查电池中给体、受体分子的构-效关系，为设计高效电池提供理论基础。

项目旨在发展创新性的量子动力学方法，并结合电子结构计算从微观原子层面上来揭示热激子的产生、迁移与分离及其相关的动力学过程。项目按计划完成了总体目标，尤其在量子动力学方法发展方面取得了重要进展。取得的主要成果为：1）提出了一个原创性的随机薛定谔方程级联方程方法，并将其拓展到线性和二维光谱、平衡关联函数等的计算；2）进一步拓展了含时波包扩散方法，并推广用于研究有机聚集体中单线态裂变过程； 3）将发展的动力学方法与电子结构计算方法相结合，提供了一套研究具体体系的计算方法和程序。本项目所发展的理论计算方法以及在有机材料中的研究得到了国际同行的认可，如美国哈佛大学和日本分子科学研究所理论化学课题组都已采用我们发展的方法研究复杂有机分子体系中的能量和电荷转移量子动力学过程，项目负责人也多次受邀参加相关学术会议。在该课题支持下共发表学术论文17篇和一些学术会议论文，共支持14位研究人员，包括12位研究生进行科研工作。