基于线性稠环类宽带隙聚合物的合成与光伏性能研究

In recent years, introduction of linear fused-ring (LFR) molecular structures featuring high charge mobility is proved to be an effective approach to improving polymer solar cells (PSCs) performance. Some typically linear fused-ring such as benzo[1,2-b:4,5-b']dithiophene (BDT), benzo[1,2-b:4,5-b']difuran (BDF) and dithieno [2,3-d;2′,3′-d′] benzo[1,2-b;4,5-b′] dithiophene (DTBDT) with high mobility play an important role in realizing high power conversion efficiency (PCE). By the method of LFR copolymerization, many wide-band gap (WBG) polymers were developed and the method has been proved to be one of successful strategies of realizing high PCE. However, for the purpose of expanding π conjugated degree from planar LFR molecules, more complicated syntheric routes are required and require higher costs. To overcome this problem, two novel LFR systems based on naphtho[2,3-b:6,7-b′]dithiophene (NDT1) and naphtho[2,3-b:6,7-b′]difuran (NDF1) building blocks featuring both large π conjugated degree and easier syntheric routes will be employed to achieve a high PCE. The target of this project will focus on exploring new WBG polymers and get insights into the effects of LFR structure on the photovoltaic performances. A series of commonly used weak electron-deficient units with planar structure will be copolymerized with NDT1 or NDF1 units with different substitutions to adjust absorption range and HOMO/LUMO level. Furthermore, some effective strategies such as two-dimentional (2-D) conjugated side chains and π bridge such as thiophene, dithiophene or thieno[3,2-b]thiophene will be adopted to finely tune polymeric crystallinity and miscibility between donor and acceptor. That means the systemic study based linear high-mobility WBG donor will accelerate the polymer photovoltaic developments in theory and in reality.

在近几年高性能聚合物光伏给体材料的设计中，通过线性高迁移率稠环结构如苯并二噻吩（BDT）、苯并二呋喃（BDF）以及二噻吩并苯二噻吩（DTBDT）等单元构筑的聚合物材料获得了较高载流子迁移率及光伏性能。这种设计思路在宽带隙聚合物给体材料中也被证明行之有效，光电转化效率不断提高。本项目将按照这种以提高迁移率为核心兼顾光、电特性的设计思路，发展一系列线性萘并二杂稠环（NDT1和NDF1）宽带隙聚合物给体。该新体系不仅可以保证有效拓展线性分子结构、扩大π共轭平面，而且可以简化合成步骤、增加官能团调控范围。在此基础上通过萘并二杂稠环与常见较高平面性的弱吸电子单元共聚来探索宽带隙给体合适的分子能级和吸收光谱。同时通过引入二维共轭侧链和共轭π桥来调控聚合物结晶性及其与受体的相容性，进一步提高光伏性能。该分子体系的系统性研究，对提高聚合物太阳能电池转化效率和拓展其实际应用具有重要的理论与实践意义。

在高性能聚合物光伏给体材料的设计中，通过线性高迁移率稠环结构如苯并二噻吩及二噻吩并苯二噻吩等线性稠环共轭单元构筑的聚合物材料获得了较高载流子迁移率及光伏性能。在本项目的研究中，按照这种以提高迁移率为核心兼顾光、电特性的设计思路，合成和表征了一系列线性萘并二杂稠环宽带隙聚合物给体。利用这些高平面、具有长共轭结构的线性稠环单元开发了数个基于此概念和体系的相似分子结构，筛选出光伏性能突出的分子体系，并做了器件优化；初步实现了二维共轭（2D）的萘并二呋喃（2D-NDF）的合成和表征；在构筑主链线性构象的分子基础上，系统地考查了不同的构筑共轭单元中给/吸电子官能团、分子量、与受体相容性等多维度影响因素，全面比较了这些因素对线性稠环结构的光谱、能级、结晶性、活性层形貌以及光伏性能的全面影响。基于NDF的聚合物给体光电转化效率达到14.21%，这个转化效率值为呋喃类光伏聚合物体系中的最高值。该分子体系的系统性研究，对提高聚合物太阳能电池迁移率、光电转化效率和拓展较低成本实际应用具有重要的理论与实践意义。