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High-performance n-type organic thermoelectrics enabled by modulating cyano-functionalized polythiophene backbones.

Junwei Wang¹, Suxiang Ma¹, Sang Young Jeong²

¹Department of Materials Science and Engineering, Southern University of Science and Technology (SUSTech), Shenzhen, Guangdong 518055, China. fengk@sustech.edu.cn.

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|November 15, 2023

Summary

Researchers developed new n-type polymers for organic thermoelectrics (OTEs). The CNg4T2-CNT2 polymer achieved a record power factor, overcoming challenges in electrical conductivity for OTE applications.

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Area of Science:

Materials Science
Organic Electronics
Thermoelectrics

Background:

N-type polymers are crucial for organic thermoelectrics (OTEs) but achieving high electrical conductivity and power factor remains a challenge.
Electron-deficient building blocks are key to developing high-performance n-type OTE materials.

Purpose of the Study:

To synthesize novel n-type polythiophene derivatives for enhanced organic thermoelectric performance.
To investigate the structure-property relationships influencing electrical conductivity and power factor in these new polymers.

Main Methods:

Synthesis of a new electron-deficient building block, CNg4T2, incorporating cyano functionalities and an intramolecular conformation lock.
Development of two n-type polythiophene derivatives (CNg4T2-2FT and CNg4T2-CNT2) using CNg4T2 with different co-units.
Characterization of polymer properties, including lowest unoccupied molecular orbital (LUMO) levels, backbone coplanarity, electrical conductivity (σ), and power factor (PF).

Main Results:

CNg4T2-CNT2 exhibits a deeper LUMO and maintained backbone coplanarity compared to CNg4T2-2FT.
CNg4T2-CNT2 films doped with N-DMBI achieved a high electrical conductivity of 13.2 S cm⁻¹ and a power factor of 10.84 μW m⁻¹ K⁻².
The achieved power factor is the highest reported for n-type polythiophenes in OTEs, outperforming benchmarks.

Conclusions:

CNg4T2 is a promising building block for high-performance n-type OTE polymers.
Fine-tuning polymer backbone structures is an effective strategy for developing advanced n-type OTE materials.
High doping efficiency and ordered polymer chain packing contribute to the superior performance of CNg4T2-CNT2.