Shanghai Institute of Ceramics Achieves Major Progress in Flexible Organic/Inorganic Thermoelectric Composites

Flexible thermoelectric energy conversion technology can transform temperature differences from the environment or the human body into electrical energy, enabling self-powered electronic devices with broad application prospects in wearable technologies. Traditional inorganic thermoelectric materials exhibit excellent thermoelectric performance but lack flexibility, while organic thermoelectric materials offer good flexibility and bendability but suffer from very low thermoelectric performance. Organic/inorganic composite thermoelectric materials combine the high thermoelectric performance of inorganic materials with the mechanical flexibility of organic materials and have become a major research focus in recent years.

One-dimensional carbon nanotubes or metal nanowires are often used in organic/inorganic thermoelectric composites because they can form conductive networks with one-dimensional polymer chains and provide efficient electrical pathways. However, their extremely low Seebeck coefficients make it difficult to improve the composite’s Seebeck coefficient. In contrast, inorganic thermoelectric materials possess high Seebeck coefficients but are typically flake- or particle-shaped, leading to poor electrical transport in composites. Therefore, selecting well-matched organic and inorganic components to achieve efficient electrical transport remains a key scientific challenge.

Recently, a team led by Researchers Shi Xun and Chen Lidong, Associate Researcher Qiu Pengfei, and Associate Researcher Qu Sanyin from the Shanghai Institute of Ceramics, Chinese Academy of Sciences, in collaboration with Professor He Jian from Clemson University, proposed a dimension-matching design strategy for thermoelectric composites. Using this approach, they developed high-performance PVDF/Ta₄SiTe₄ organic/inorganic flexible thermoelectric composite films. The prototype device achieved the highest reported normalized maximum power density among flexible thermoelectric devices under a temperature difference of 35.5 K. The results were published in Energy & Environmental Science under the title:

“Conformal Organic–Inorganic Semiconductor Composites for Flexible Thermoelectrics.”

Dimension-Matching Design Strategy

Polyvinylidene fluoride (PVDF) is a flexible insulating polymer with a one-dimensional chain structure. Following the dimension-matching concept, the team selected Ta₄SiTe₄, an inorganic material with a similar one-dimensional structure, to form an organic/inorganic flexible composite film.

• Ta₄SiTe₄ whiskers with 0.5% Mo doping at the Ta site were synthesized via chemical vapor transport.
• N,N-dimethylformamide (DMF) was used as a dispersant.
• Composite films were fabricated by drop-casting PVDF/Ta₄SiTe₄ suspensions.

Scanning electron microscopy showed that Ta₄SiTe₄ whiskers were uniformly dispersed in the PVDF matrix, forming a network structure. Transmission electron microscopy confirmed tight interfacial bonding between the whiskers and PVDF.

Thermoelectric Performance

The PVDF/50 wt% Ta₄SiTe₄ composite exhibited excellent electrical transport performance:

• Power factor up to 1060 μW·m⁻¹·K⁻² at 220 K
• Significantly higher Seebeck coefficient than composites based on carbon nanotubes or metal nanowires at the same electrical conductivity

These improvements arise from the semiconductor transport properties and one-dimensional structure of Ta₄SiTe₄.

Flexibility and Device Performance

The composite film also demonstrated outstanding flexibility:

• No significant resistance change after 5,000 bending cycles on a 9 mm diameter curved surface

A prototype thermoelectric device containing four PVDF/50 wt% Ta₄SiTe₄ thermoelectric couples achieved:

• Normalized maximum power density: 0.13 W·m⁻¹ at ΔT = 35.5 K
• The highest value reported for flexible thermoelectric devices

Funding and Support

This research was supported by the National Key R&D Program of China, the National Natural Science Foundation of China, the Chinese Academy of Sciences Youth Innovation Promotion Association, and the Shanghai Rising-Star Program.

Article link: https://doi.org/10.1039/c9ee03776d

(a) Schematic of the PVDF/Ta₄SiTe₄ flexible composite film.

(b) Comparison of thermoelectric performance between PVDF/Ta₄SiTe₄ composite films and previously reported one-dimensional organic–inorganic composite films.

(c) Comparison of normalized maximum power density of PVDF/Ta₄SiTe₄-based prototype thermoelectric devices with previously reported flexible thermoelectric devices.