Selenium Substitution in Bithiophene Imide Polymer Semiconductors Enables High‐Performance <i>n</i>‐Type Organic Thermoelectric
Jianfeng Li, Min Liu, Kun Yang, Yimei Wang, Junwei Wang, Zhicai Chen, Kui Feng, Dong Wang, Jianqi Zhang, Yongchun Li, Han Guo, Zhixiang Wei, Xugang Guo
Abstract
Abstract Designing n ‐type polymers with high electrical conductivity remains a major challenge for organic thermoelectrics (OTEs). Herein, by devising a novel selenophene‐based electron‐deficient building block, the pronounced advantages of selenium substitution in simultaneously enabling advanced n ‐type polymers is demonstrated with high mobility (≈2 orders of magnitude higher versus their sulfur‐based analogues due to both intensified intra‐ and inter‐chain interactions) and much improved n ‐doping efficiency (enabled by the largely lowered LUMO level with a ≈0.2 eV margin) of the resulting polymers. Via side chain optimization and donor engineering, the selenium‐substituted polymer, f‐BSeI2TEG‐FT, achieves a highest conductivity of 103.5 S cm −1 and power factor of 70.1 µW m −1 K −2 , which are among the highest values reported in literature for n ‐type polymers, and f‐BSeI2TEG‐FT greatly outperformed the sulfur‐based analogue polymer by 40% conductivity increase. These results demonstrate that selenium substitution is a very effective strategy for improving n ‐type performance and provide important structure‐property correlations for developing high‐performing n ‐type OTE materials.