Optimizing the Thermoelectric Performance of Poly(3-hexylthiophene) through Molecular-Weight Engineering
Optimizing the Thermoelectric Performance of Poly(3-hexylthiophene) through Molecular-Weight Engineering
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通过分子量工程优化聚（3-己基噻吩）的热电性能
DOI：
10.1002/asia.201801080
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发表时间：
2018
期刊：
影响因子：
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通讯作者：
Lidong Chen
中科院分区：
文献类型：
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作者：
Sanyin Qu;Qin Yao;Wei Shi;Yanling Chen;Lidong Chen
制备了不同分子量的聚3-己基噻吩（P3 HT）薄膜，并对其分子结构和热电性能进行了研究。发现P3 HT的分子量通过影响分子结构而对载流子传输性质具有重要影响，并且因此也对TE性能具有影响。P3 HT薄膜的电导率随着分子量的增加先增加后降低，而Seebeck系数保持在相同的水平。结果，P3 HT-M50 k（MW约50 000 g mol-1）薄膜的电导率达到（103.8±1.2）S cm，比P3 HT-M10 k（MW约10 000 g mol-1）的电导率高出20倍以上，比电导率高出近30% P3 HT-M100 k（MW约100 000 g mol-1）。 因此，P3 HT ‐ M50 k在室温下的最大TE功率因数高达（22.6±0.6）μW mK−2，远高于P3 HT ‐ M10 k或P3 HT ‐ M100 k。 结合C-AFM的微观结构分析表明，在低分子量的薄膜中，大部分有序区域和非晶区域之间的载流子输运是不连通的，这导致了高的迁移势垒和差的载流子迁移率。在增加分子量时，长分子链提供足够的连接性以使电荷移动通过有序区域，这降低了载流子势垒并增加了载流子迁移率。因此，电导率和塞贝克系数均得到显著改善。然而，过高的分子量可能导致聚合物链的更多折叠，这将使电传输性能恶化。实验结果不仅揭示了分子量对导电聚合物电输运性能的内在影响，而且表明分子量工程是设计和筛选高性能聚合物TE材料的有效途径。
Poly(3‐hexylthiophene) (P3HT) films with various molecular weights (MWs) were successfully prepared, and both their molecular structures and thermoelectric (TE) properties were investigated. It was found that the molecular weight of P3HT had an important effect on the carrier‐transport properties by affecting the molecular structure and, as a result, also had an effect on the TE performance. The electrical conductivity of the P3HT films first increased upon increasing the molecular weight and then decreased at high molecular weights, whereas the Seebeck coefficient remained at the same level. As a result, the P3HT‐M50k(MW≈50 000 g mol−1) film reached an electrical conductivity of (103.8±1.2) S cm, which is more than 20 times higher than the electrical conductivity of P3HT‐M10k(MW≈10 000 g mol−1) and almost 30 % higher than the electrical conductivity of P3HT‐M100k(MW≈100 000 g mol−1). Consequently, the maximum TE power factor of P3HT‐M50kat room temperature was as high as (22.6±0.6) μW mK−2, which is much higher than that of either P3HT‐M10kor P3HT‐M100k. Microstructure analysis combined with C‐AFM suggested that carrier transport between most of the ordered and amorphous regions was unconnected in films with low molecular weights, and this resulted in a high migration barrier and poor carrier mobility. Upon increasing the molecular weight, the long molecular chain provided enough connectivity for the charge to move through the ordered regions, which decreased the carrier barrier and increased carrier mobility. Therefore, both the conductivity and Seebeck coefficient were significantly improved. However, a too‐high molecular weight could cause more folding of the polymer chain, which would deteriorate the electrical‐transport properties. The experimental results not only reveal the intrinsic effect of molecular weight on the electric transporting properties of conducting polymers but also suggest that molecular‐weight engineering is an effective way to design and screen high‐performance polymer TE materials.