有机能源材料电子态的本质

Benefiting from a rapid development of nonfullerene acceptors (NFAs), remarkable progresses have been achieved in the field of organic energy materials in the last three years. High performances in the state-of-the-art NFA-based devices have stimulated the urgency in elucidating the fundamental mechanism whose characteristics are significantly different from those in conventional fullerene-based systems. Understanding the nature of excited electronic states is pivotal in uncovering the working principles in these devices. Toward this aim, we combine a team of experts devoting in the field of organic optoelectronics with specialties in quantum and molecular dynamics and ultrafast spectroscopy. In this project, we will focus on unveiling the microscopic mechanism by exploring the nature of excited states during optoelectronic conversions. In detail, we will investigate the ultrafast dynamics of the formation, dissociation and recombination of photogenerated electron-hole pairs with different configurations, develop a dynamical model for the carrier transport, and establish the structure-property relationship with in-depth surveys on molecular morphology. By theoretical and experimental efforts, we will reveal the fundamental working mechanisms of devices, propose new schemes for the rational designing of materials and devices, and uncover new concepts to intrinsically improve the efficiency of devices.

近三年来，有机光伏材料特别是非富勒烯体系的研究得到快速发展，取得了令人瞩目的成就。器件效率的快速提升对工作机理的理解、器件结构的优化提出了新的挑战，非富勒烯受体光伏材料展现出许多不同于传统富勒烯体系的特性，探索该类材料中电子态的本质成为理解内在机理的核心任务。为此，本项目团队集合了在有机光伏材料中工作多年的量子动力学和分子动力学、以及超快光谱学的研究者。在前期研究工作的基础上，本项目以揭示有机能源材料光电转换过程中电子态的本质与光电转换微观机理为总体研究目标，结合超快光谱实验与理论模型/计算模拟方法，研究光生电子空穴对的多种形态及其产生、解离与复合的超快动态过程，构建载流子输运的动力学模型，定量刻画分子堆积的微观形貌对关键物理过程的调控，诠释有机光电转换器件工作的基本原理，提出调控材料设计和器件结构的新方案，探寻从根本上提升器件效率的新原理。

得益于非富勒烯受体的发展，有机光伏电池效率得到迅猛提升，并展现出不同于传统富勒烯体系的特性。尤其令人感到迷惑的是，即使在低的激子解离驱动力下，光生电荷产率也非常高。本项目通过结合理论模拟和超快光谱等表征技术，系统研究了高效有机光伏体系的激发态本质和动力学过程。发现极化效应可显著降低基于A-D-A受体有机光伏电池的电荷分离势垒，揭示了低驱动力下自由电荷的高效产生机理。阐明分子骨架、端基和侧链结构对A-D-A受体分子聚集行为和取向的重要影响，发现小分子聚合化受体的电子传输性能决定于分子内超交换和分子间直接耦合的共同作用。提出端基π-π堆积的分子间策略，有效减小A-D-A受体单/三线态能级差、抑制三线态电荷复合，同时保持强的光吸收能力。发现寡聚体分子内单线态裂分新通道，主要借助空间分离的三线态激子对生成自由的三线态，从而破解三线态激子对的产生和分离之间的矛盾。研究结果揭示了有机光电转换的新机理，为分子优化设计进一步提升有机光伏性能给出了新思路。