Donor-Bridge-Acceptor的分子内电荷转移对有机光伏电池中激子的分离机制研究

Organic photovoltaic (OPV) cells become the important object on research and development of the next generation solar cells due to their simple production process, low cost, flexibility, as well as large-scale production. In order to further improve the power conversion efficiency, making great efforts are needed to understanding the dissipation of charge transfer (CT) exciton which determine the OPV properties. In this project, series samll molecules as donor material with the structure of donor-bridge-acceptor will be designed and synthesized. These molecules are used to study the mechanism of exciton dissociation in OPV cells. Firstly, the effects on intramolecule charge transfer state (ICT) of these molecules by different bridge group will be investigated, and the relationship between ICT and bridge group will be established. Secondly, charge transfer (CT) exciton dissociation will be investigated in donor/acceptor (Fullerene derivatives) system, and then the effects on CT exciton dissociation by the bridge group are discussed. Thirdly, the relationship between ICT exciton and CT exciton dissociation will be studied with the bridge group as a link. Finally, a valuable design principle for donor materials based on the structure of donor-bridge-acceptor will be constructed, which will provide new idea and direction for the development of donor materials and OPV cells.

有机光伏电池(OPV)具有易于实现大面积、柔性、低成本等优点，成为新型太阳能电池研究中的重点之一。为了进一步提高OPV的效率，有必要对决定OPV性能的激子分离机制进行深入系统的研究。本项目将针对此问题，拟通过设计、合成一系列具有donor-bridge-acceptor(d-b-a)结构的小分子给体材料，以这些分子的激发态特征为出发点研究OPV中激子的分离机制。首先研究不同类型的 “桥”(bridge)基团对分子内电荷转移 (ICT) 的影响，建立“桥”基团与ICT态的关系。其次研究给体/受体(富勒烯衍生物)体系的分子间电荷转移(CT)激子分离情况，分析“桥”基团的类型对CT激子分离的影响，然后以“桥”基团为纽带了解ICT激子类型与CT激子分离性能的相关性。最后，结合实验与理论分析的结果指出以d-b-a为模块构建的给体分子与光伏器件性能之间的构效关系，为给体材料分子的设计提供有益指导。

本项目对OPV给体材料分子以桥为特征的构效关系进行研究。设计并合成基于donor-bridge-acceptor(d-b-a)模型的分子。研究桥(b)基团对材料分子激子分离的影响；通过结合实验测试与理论分析结果，以桥(b)基团为纽带，探讨分子内电荷转移态(ICT)特征对给受体间电荷转移的影响。在本项目的研究内容主要围绕以下四类桥基团的d-b-a分子展开研究工作。(1) 桥基团长度；研究表明，桥基团为两个噻吩单元时(2T)，其ICT态具有较大的电荷转移距离，使分子内电子-空穴对的库伦作用降低，有利于分子内电子-空穴对的分离，从而促进光电流产生。(2) “混合型”(调节桥单元顺序)共轭桥；噻并噻吩(TT)单元联接于a基团的结构，为给体分子TTRD。相对于噻吩(T)单元联接于a基团的分子TRD，其具有较小的ICT激子束缚能，光诱导下，TTRD/受体(A)系统易于电子转移。(3) 不同电负性的桥单元；相对于无桥单元或乙炔基为桥单元的分子，以噻吩为桥单元的TDR分子ICT态电子-空穴对束缚较弱，有利于分子内电子-空穴对的分离，则在TDR/A体系中，TDR分子中的电子易转移的受体材料分子上。(4) “X型”桥基团；联蒽为桥基团的TBAR分子中，d基团与a基团之间去耦合，HOMO/LUMO轨函分布完全分离。其全面的理论计算分析和光伏器件研究正在进行。