有机光伏体系中激子耦合与激子动力学的理论研究

The magnitude of the excitonic couplings is closely related with the dynamic processes of the generation, diffusion and dissociation of the excitons in organic photovoltaics (OPV), and its accurate computation relies on the characterization of the electronic excited states in the aggregates of molecules (polymers). Limited by the computational complexities caused by the condensed phase structures and the complicated photo-physics mechanism in OPV, their characterizations by conventional quantum chemical methods are currently infeasible, greatly hindering the understanding for (strong) excitonic couplings and exciton dynamics. To solve this problem, we plan to build a quantitative modeling scheme for the electronic excited state processes in OPV: we will develop efficient methods for characterizing the electronic structures of excited states (low-scaling algorithm for electronic excited states, constructing diabatic basis, calculating strong excitonic coupling), and further combine molecular dynamics simulation to construct a quantitative exciton-phonon model, which will be used for quantum dynamics simulation of ultrafast processes of excited states. In this project, this scheme will be used for the simulation of two key ultrafast processes in OPV: exciton diffusion and exciton dissociation. The quantum coherent mechanism and its factors are expected to be disclosed by such simulations, providing theoretical aspects for the molecular design and device optimization in OPV. The theoretical scheme built in this project will be also suitable for the future study of biological photosynthetic systems and other optoelectronic materials.

激子间耦合强度的大小与有机光伏体系中的激子产生、迁移、解离等动力学过程及其新颖量子相干机制紧密相关，对其可靠计算依赖于对（高）分子聚集体电子激发态的精确表征。受限于有机光伏体系的凝聚相结构和复杂光物理机制带来的计算复杂度，其常规量子化学表征目前还很难实现，严重制约了人们对（强）激子耦合及激子动力学的认识。针对这一问题，本项目拟发展有机光伏体系电子激发态过程的定量模拟方案：发展高效的激发态电子结构表征方法（低标度激发态算法，复杂透热基矢的构建，强激子耦合的计算），结合分子动力学模拟构筑激子-声子定量模型，并基于此进行激发态超快过程的量子动力学模拟。在本项目中，该方案将被用于对有机光伏体系中激子迁移和激子解离两种关键超快过程的动态模拟，以揭示其量子相干机制及影响因素，为有机太阳能电池的分子设计与器件优化提供理论基础。该课题建立的理论方案也适用于将来对生物光合作用系统和其他光电材料的研究。

由于计算自由度众多，光电材料和生命体系中的激发态过程的理论模拟往往依赖于激子模型。但是，凝聚相激子模型的精确构建和求解仍是理论难题。针对上述挑战，本项目主要开展了两方面工作。首先，发展理论新方法，高精度描述激发态电子结构及其与振动（声子）之间的耦合，实现大体系模型的高效量子动力学实时演化和二维光谱模拟。其次，应用新方法研究实际光电材料中的聚集体发光、单线态裂分、光催化等各种光物理化学过程，揭示其微观机制；并结合机器学习和高通量计算将机理研究成果应用于对有机光伏分子的设计与筛选。本项目成果为后续各类光化学体系的研究提供了理论工具和参考。