基于苝酰亚胺的新型三维受体材料的设计、合成及其在太阳能电池中的应用

Over recent decades, the chemistry and material science communities have witnessed a steadily increasing interest in perylene bisimides (PBIs) due to their remarkable electro-optical properties and potential applications in optoelectronic devices such as organic field-effect transistors and organic solar cells. Despite the variety of excellent properties, progress of organic solar cells based on PBIs has often been hampered due to the strong stacking tendency of PBIs to form large aggregates, which prevents efficient exciton splitting at the donor and acceptor interfaces. To suppress the aggregation of PBI-based acceptors without adversely affecting the charge transport properties, non-planar perylene architecture emerges as the most efficient design concept. Generally, there are three major strategies to achieve this: (1) functionaliztion of perylene cores by sterically hindered substitutions in the bay or nonbay regions. (2) hydrazine-linked PBI dimers in which the two PBI units are oriented perpendicularly to each other due to the repulsion of electron clouds on oxygen atoms. (3) PBI oligomers linked in the bay regions via single bond, ethylene bridge, or aromatic linker. Recently we found that compared with PBIs linked by single bond or aromatic linker, fully-conjugated three-dimensional (3D) perylene bisimide derivatives usually have a much broader and higher absorption spectrum, which will lead to a higher short-circuit current (JSC). Meanwhile, fully-conjugated 3D perylene bisimide derivatives have evenly distributed energy levels just like fullerene, which are in favour of the electron transport. However, it should be noted that the fully-conjugated structures usually lead to a much lower LUMO levels. In order to take full use of the advantages and avoid the disadvantages from the fully-conjugated structures, the rational design strategy is very important. In this project, we present a new 3D fully-conjugated molecular architecture that consists of PBI subunits adjoining plane polycyclic aromatic hydrocarbons or curved corannulene, which has fullerene-liked structures. The design, synthesis and applications based on them as acceptors for organic solar cells will be studied. From the relationships of molecular structure—self-assembly—photovoltaic properties, the optimal 3D fully-conjugated molecular architecture will be chosen to do the modification and the extension of conjugated backbones. This project will supply new promising molecular skeletons and design strategies for high-performance non-fullerene organic solar cells.

苝酰亚胺类分子由于其独特的光电性质及热稳定性，是有机场效应晶体管、有机太阳能电池等分子器件的关键材料。然而，以苝酰亚胺类分子作为受体材料所制得的太阳能电池却往往表现出较低的能量转换效率，主要是由于其具有平面结构，分子与分子之间易于堆积而形成较大的晶粒，从而抑制了激子在给受体界面的有效分离。本项目从新的设计理念出发，将设计合成一系列具有类似于富勒烯结构的，三维刚性共轭苝酰亚胺受体材料，并对该材料的合理设计与可控制备、分子结构-聚集态结构，分子结构-光伏性能关系、器件结构-光伏性能关系等进行研究，优化筛选出各项性能优异的三维共轭苝酰亚胺分子骨架，并对其进行进一步地修饰和共轭骨架的扩展，深入地探索其作为受体材料在太阳能电池中的应用。本项目的研究将为开发高性能的非富勒烯太阳能电池提供新的材料和设计思路。

苝酰亚胺类分子被认为是最具潜能的替代富勒烯的电子受体材料之一。虽然苝酰亚胺类分子具有诸多优点，但将其作为受体材料所制得的太阳能电池往往表现出较低的能量转换效率，主要是由于其具有平面结构，分子间易于堆积形成较大晶粒，从而抑制了激子在给受体界面的有效分离。为了得到基于苝酰亚胺的非平面受体材料，往往采用以下三种设计策略：（1）对苝酰亚胺本身进行修饰，如在其bay位或nonbay位引入大位阻基团使其扭曲，抑制分子间的相互作用。（2）通过联氨桥将两个苝酰亚胺分子头对头连在一起。(3) 通过在bay位或nonbay位引入不同的链接单元（linker）实现苝酰亚胺分子低聚物的合成。到目前为止，虽然基于非平面的苝酰亚胺受体材料已有一些报道，但通过传统设计理念所得到的苝酰亚胺受体材料种类仍十分有限，制得的太阳能电池的能量转换效率普遍偏低，无法满足应用的要求。要想得到可以与富勒烯受体材料相媲美甚至超越其性能的苝酰亚胺类分子，迫切需要在新的设计策略下新结构和新材料的出现。本项目从新的设计理念出发，将螺烯结构引入到稠环分子中，得到了立体拓扑结构可控的“三叶螺旋桨”多重螺烯稠环芳酰亚胺，并对分子的对称性、光电性质、组装行为进行了深入研究，以该类分子作为受体材料的太阳能电池呈现出9.28%的高能量转换效率，在基于芳酰亚胺的太阳能电池受体材料体系中处于领先水平；为获得具有多重螺烯结构的稠环芳酰亚胺，首次提出“多核驱动”的设计策略，并成功地得到了立体拓扑结构可控的“双核”驱动六重[5]螺烯结构，以该类分子作为受体的太阳能电池的能量转换效率提升到10%以上；运用将具有平面和曲面的有机共轭分子进行杂化的设计策略，得到了“五叶花瓣状”构型的五重[6]螺烯稠环芳酰亚胺，以其作为受体材料制得的太阳能电池的光电转换效率进一步提升到11%以上。本项目的研究将为开发高性能的非富勒烯太阳能电池提供新的材料和设计思路。