n-Type polymers with deep-positioned lowest unoccupied molecular orbital (LUMO) energy levels are essential for enabling n-type organic thin-film transistors (OTFTs) with high stability and n-type organic thermoelectrics (OTEs) with high doping efficiency and promising thermoelectric performance. Bithiophene imide (BTI) and its derivatives have been demonstrated as promising acceptor units for constructing high-performance n-type polymers. However, the electron-rich thiophene moiety in BTI leads to elevated LUMOs for the resultant polymers and hence limits their n-type performance and intrinsic stability. Herein, we addressed this issue by introducing strong electron-withdrawing cyano functionality on BTI and its derivatives. We have successfully overcome the synthetic challenges and developed a series of novel acceptor building blocks, CNI, CNTI, and CNDTI, which show substantially higher electron deficiencies than does BTI. On the basis of these novel building blocks, acceptor-acceptor type homopolymers and copolymers were successfully synthesized and featured greatly suppressed LUMOs (-3.64 to -4.11 eV) versus that (-3.48 eV) of the control polymer PBTI. Their deep-positioned LUMOs resulted in improved stability in OTFTs and more efficient n-doping in OTEs for the corresponding polymers with a highest electrical conductivity of 23.3 S cm-1 and a power factor of ∼10 μW m-1 K-2. The conductivity and power factor are among the highest values reported for solution-processed molecularly n-doped polymers. The new CNI, CNTI, and CNDTI offer a remarkable platform for constructing n-type polymers, and this study demonstrates that cyano-functionalization of BTI is a very effective strategy for developing polymers with deep-lying LUMOs for high-performance n-type organic electronic devices.
Bibliographical noteFunding Information:
K.F. acknowledges the financial support by the National Natural Science Foundation of China (no. 22005135) and the Shenzhen Basic Research Fund (no. JCYJ20190809162003662). H.G. acknowledges the financial support from the National Natural Science Foundation of China (no. 51903117). X.G. is thankful for the financial support from the Shenzhen Basic Research Fund (no. JCYJ20180504165709042). H.Y.W. is grateful for the financial support from the National Research Foundation (NRF) of Korea (NRF-2016M1A2A2940911 and 2019R1A6A1A11044070). We also acknowledge the assistance of SUSTech Core Research Facilities and the support by the Center for Computational Science and Engineering at SUSTech.
ASJC Scopus subject areas
- General Chemistry
- Colloid and Surface Chemistry