芴稠硫系杂芳环类聚合物给体聚集态结构与其高效光电转换性能

An outstanding challenge for the development of high-performing polymer solar cell is to arrange molecules in a manner that optimizes all relevant optoelectronic processes required for efficient operation. Fundamental understanding and characterization of aggregated structure of polymer donors, in particular, correlating with photovoltaic device characteristics becomes increasingly important. D-A alternating copolymer donors with annulated backbones between fluorene and chalcogen-containing hetero aromatics have extended π-conjugated backbones and exists certain dihedral angle between 9,9-alkyl chains located on fluorene skeleton and the entire extended π-conjugated backbones. The interplay of interactions of such alkyl chains and π-π stacking interaction from the extended conjugated backbones renders these polymer donors aggregate in a different way, which may result in special effects on the performance of polymer solar cells. Our preliminary research showed that a D-A alternating copolymer based on fluorene-thienothiophene annulated conjugated backbone can provide an PCE up to 9% with high stability. Based on this discovery, in this project, the design, synthesis and photovoltaic properties of novel D-A alternating copolymers based on annulated conjugated backbones between fluorene and chalcogen-containing hetero aromatics will be carried out. Under the interplay of inherited low-lying HOMO levels of polyfluorenes, enlarged π conjugation and enhanced intermolecular interactions, the effect of D-A alternating copolymerization on tuning energy levels of resulting polymers and the morphological features, these novel D-A copolymers will be endowed advantageous photovoltaic properties. The understanding of the characteristics of aggregated structures of these polymers and their relationship to device performance, may aid in the design of new high-performance polymers for optoelectronics.

调节聚合物太阳能电池异质结薄膜中给受体分子堆叠，获得对应于高效光电转换过程的微纳尺度特定聚集态结构，具有非常重要的科学意义。芴稠硫系杂芳环新结构，通过芴与硫系杂芳环稠结扩展π共轭骨架，母核芴骨架9,9-位烷基链和扩展π共轭骨架形成一定二面夹角，处于该空间位置的烷基链间相互作用和扩展共轭骨架间π-π堆叠共同作用，使其D-A型聚合物在聚集态结构方面体现出与烷基链和共轭骨架基本在同一平面的D-A型聚合物不同的堆叠状态。项目前期研究显示，基于芴稠噻吩并噻吩结构的D-A型聚合物电池，能量转换效率可达9%，并具有良好性能稳定性。申请项目拟选择不同硫系杂芳环和芴实现稠接，获得芴稠硫系杂芳环类新型给体单体，通过给受交替共聚获得具有低HOMO能级、窄带隙聚合物给体，研究其聚集态结构特征和成因及其对光电转换性能影响规律，为获得具有特定聚集态结构并能调控对应器件性能的新型高效聚合物电池给体提供科学技术支持。

项目针对激子机制约束的聚合物太阳能电池光电转换各个物理化学过程与给受体材料电子结构、聚集态结构间强耦合，将共轭骨架拓展与仅在共轭骨架中心引入含有面外大支链结构烷基侧链的sp3桥碳分子相结合的设计方法，平衡分子堆叠聚集能力与溶解分散加工性能，开展芴稠硫系杂芳环类新型梯型电子给体结构单元、对应聚合物给体的设计制备、聚集态结构和光电转换性能研究。.通过取代烷基侧链、共轭骨架氟代效应等分子工程，构建二元和三元体系聚合物：富勒烯体异质结电池器件，获得了具有最高光电转换性能之一的芴稠硫系杂芳环类梯形结构D-A共聚物给体。从聚合物给体催化聚合制备时催化剂选择优化的重要性、分子堆叠对聚合物共轭骨架构型微小空间扭曲的敏感性、共轭骨架多元氟代效应等方面，以及体异质结薄膜溶液加工添加剂分子结构工程，将材料分子设计合成、聚集态结构和电池器件物理综合，归纳分子结构调构、聚合物结构调构带来的对聚合物半导体材料电子结构和聚集态结构以及电池器件性能影响规律，提炼出高性能聚合物给体材料分子结构-聚集态结构-光电转换性能相互关系及其分子结构工程基本原则，为通过分子工程获得在时间、空间和能量状态上具有与电池器件激子工作机制各过程相适配的优化的电子结构和聚集态结构、实现性能增强提供指导。