Shanghai Institute of Ceramics Achieves New Progress in Organic Thermoelectric Materials Research

Organic polymer thermoelectric materials are an emerging class of clean energy materials capable of directly converting heat into electricity. These materials are solution-processable, lightweight, low-cost, and highly flexible, offering strong potential for wearable electronics applications. Compared with inorganic thermoelectric materials, polymer thermoelectrics suffer from limited material varieties and low thermoelectric conversion efficiency, mainly due to an insufficient understanding of the relationship between molecular structure and thermoelectric performance. Chemical doping is the primary method for enhancing polymer conductivity and tuning thermoelectric properties. However, current polymer semiconductors exhibit low doping efficiency, and high doping concentrations tend to disrupt polymer packing, significantly reducing carrier mobility. As a result, high electrical conductivity cannot be achieved without sacrificing the Seebeck coefficient, severely limiting improvements in thermoelectric device performance.

Recently, Associate Researcher Li Hui and Researcher Chen Lidong from the Shanghai Institute of Ceramics, Chinese Academy of Sciences (SICCAS), employed a random copolymerization strategy of functional building blocks. By copolymerizing donor–acceptor units with bithiophene donor units via the Stille coupling reaction, they developed a series of novel conductive polymers. This approach enabled the synergistic optimization of high doping efficiency and carrier mobility, providing a new structural design strategy for high-performance polymer thermoelectric materials.

The research was published in the internationally renowned journal Advanced Functional Materials under the title:

“Synergistically Improved Molecular Doping and Carrier Mobility by Copolymerization of Donor–Acceptor and Donor–Donor Building Blocks for Thermoelectric Application”

(Article link: https://onlinelibrary.wiley.com/doi/10.1002/adfm.202070270) and was selected as the issue’s back cover.

Structural Features of the New Materials

The new materials exhibit the following chemical structure characteristics:

1. Enhanced interchain packing through electrostatic interactions between donor–acceptor units.

2. Improved doping efficiency via alkoxy-functionalized bithiophene donor units.

3. Increased Seebeck coefficient through backbone irregularity introduced by random copolymerization.

Compared with conventional polythiophene semiconductors (which have low intrinsic mobility and become brittle at high doping levels) and donor–acceptor alternating polymers (which are difficult to dope and suffer mobility loss at high doping), the functional building-block copolymerization strategy integrates the advantages of different polymer units. This ensures good crystallinity while achieving high doping efficiency. As a result:

• Carrier mobility remains above 1 cm²·V⁻¹·s⁻¹ even at high doping concentrations.
• Carrier concentration reaches 10²⁰–10²¹ cm⁻³.
• Highly conductive flexible films are obtained.

Moreover, random copolymerization reduces backbone regularity, resulting in a higher Seebeck coefficient than fully thiophene-based polymers. The final power factor exceeds 110 μW·K⁻²·m⁻¹, demonstrating that random copolymerization of functional building blocks is an effective strategy for developing next-generation high-performance thermoelectric materials.

This research was supported by the National Major Research Program, the National Natural Science Foundation of China, and the Shanghai Yangfan Program. Associate Researcher Li Hui is the first and corresponding author, and Researcher Chen Lidong is the co-corresponding author.

Relationship between Chemical Doping Characteristics and Thermoelectric Parameters for Conventional Polythiophene-Based Polymers (top), Donor–Acceptor Alternating Polymers (middle), and the Newly Designed Polymers in This Work (bottom)

Trends in Hall Mobility and Carrier Concentration with Increasing Doping Level, and the Resulting Thermoelectric Performance of the Polymers