三元共聚物热电材料的设计合成及其链结构对热电性能的调控

The solution-processing thermoelectric polymers are mainly obtained by the polymerization of the thiophene monomers and usually show low carrier mobility. Their thermoelectric performance is far lower than those of traditional materials such as PEDOT:PSS, polyaniline, polypyrrole and so on. One of reasons is that the interaction between polymer and dopant in solid state is still unclear. On the other hand, the key parameters in thermoelectric device, electrical conductivity and Seebeck coefficient, are oppositely dependent on the carrier concentration. Chemical doping can improve the electrical conductivity but significantly decrease Seebeck coefficient, which finally results in a low power factor. Therefore, it is crucial to know how to prepare conductive polymers with high electrical conductivity and high Seebeck coefficient. Also, it is important to discover the effect of microstructure on these parameters. In our previous work, we have demonstrated that high mobility of the conductive polymer is essential for efficiently improving the power factor. In this project, we will synthesize ternary copolymers with high mobilities by copolymerizing diketopyrrolopyrrole with donor monomers together. Based on the oxidation ability of the building blocks and the polarity of the side chains, we will change the composition ratio to adjust the crystallinity of the films. And then, the crystalline polymer film will be selectively doped and interpenetrating networks morphology is expected in which high-level doping areas and low-level doping areas are homogeneously distributed. We aim to obtain high-performance thermoelectric devices with high electrical conductivity and enhanced Seebeck coefficient. Finally, the relationship and physical mechanism between the chemical structure and thermoelectric parameters will be investigated.

可溶液加工聚合物热电材料体系单一，主要以噻吩类聚合物为主，这类材料载流子迁移率较低，而且通过溶液法掺杂的器件性能远低于PEDOT:PSS、聚苯胺、聚吡咯等传统材料。一方面是由于目前对聚合物和掺杂剂之间的作用机制缺乏深入理解；另一方面，化学掺杂可以获得高电导但泽贝克系数显著降低，最终限制了功率因子的提高。如何通过结构设计制备具有高电导并保持较高泽贝克系数的聚合物、探明微结构对热电参数的影响机制是热电材料化学领域的关键科学问题。申请人前期研究成果表明，高载流子迁移率是获得高功率因子的前提。本项目拟通过三元共聚方式合成含有吡咯并吡咯二酮单元的给受体型高迁移率共聚物；利用构筑单元化学结构以及侧链极性差异，通过改变投料比例调控聚合物的结晶行为，使薄膜实现局域性掺杂，形成高掺杂区和低掺杂区互穿网络结构，从而制备高电导、高泽贝克系数兼具的热电转换器件，并探明化学结构、微观形貌与热电参数的关联机制。

未来电子器件提出异形化、柔性化、微型化的应用需求，可溶液加工的聚合物热电材料成为理想的材料选择之一。目前聚合物热电材料种类匮乏，热电性能依然远低于无机材料。一方面是由于对聚合物和掺杂剂之间的作用机制缺乏深入理解；另一方面，化学掺杂可以获得高电导但泽贝克系数显著降低，最终限制了功率因子的提高。如何通过结构设计制备具有高电导并保持较高泽贝克系数的聚合物、探明微结构对热电参数的影响机制是有机热电领域的关键科学问题。本项目在分子结构设计上，提出了主侧链结构设计性结合的功能基元共聚合成策略，实现了载流子浓度与载流子迁移率的同步提升，为高性能聚合物热电材料结构设计建立了普适性设计、筛选策略；在薄膜微纳尺度上，利用化学掺杂涨落以及微观结构调控降低载流子传输势垒，实现了电导率进一步提升，最终获得了多种功率因子大于80 μW K-2 m-1的新型聚合物半导体材料，最大功率因子达到110 μW K-2 m-1。本项目探明掺杂剂在聚合物链中的作用位置和作用机理，建立了掺杂剂和聚合物链相互作用对电荷传输影响的相关模型；揭示了薄膜中微观结构和聚集态对热电转换器件参数的影响，为高性能聚合物热电材料结构设计和器件优化提供依据。