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Thursday, 23 Nov 2017

NREL research sees significant advances in carbon nanotube thermoelectric performance

The addition of thin films to fabrics could power portable electronics and sensors

NREl - SWCNT composite as primary material for efficient thermoelectric generators

31 Oct 2017 | Editor

Scientists at the U.S. Department of Energy's National Renewable Energy Laboratory (NREL) have reported significant advances in the thermoelectric performance of organic semiconductors based on carbon nanotube thin films that could be integrated into fabrics to convert waste heat into electricity or serve as a small power source.

The research demonstrates significant potential for semiconducting single-walled carbon nanotubes (SWCNTs) as the primary material for efficient thermoelectric generators, rather than being used as a component in a "composite" thermoelectric material containing, for example, carbon nanotubes and a polymer.

According to Jeffrey Blackburn, a senior scientist in NREL's Chemical and Materials Science and Technology center and co-lead author of the paper with Andrew Ferguson - there are some inherent advantages to doing things this way.

These advantages include the promise of solution-processed semiconductors that are lightweight and flexible and inexpensive to manufacture.

The introduction of SWCNT into fabrics could serve an important function for "wearable" personal electronics. By capturing body heat and converting it into electricity, the semiconductor could power portable electronics or sensors embedded in clothing.

Blackburn and Ferguson already published two papers last year on SWCNTs, and the new research builds on their earlier work.

  • The first paper: in Nature Energy, showed the potential that SWCNTs have for thermoelectric applications, but the films prepared in this study retained a large amount of insulating polymer
  • The second paper: in ACS Energy Letters, demonstrated that removing this "sorting" polymer from an exemplary SWNCT thin film improved thermoelectric properties

The newest paper revealed that removing polymers from all SWCNT starting materials served to boost the thermoelectric performance and lead to improvements in how charge carriers move through the semiconductor.

The paper also demonstrated that the same SWCNT thin film achieved identical performance when doped with either positive or negative charge carriers. These two types of material--called the p-type and the n-type legs, respectively--are needed to generate sufficient power in a thermoelectric device. Semiconducting polymers, another heavily studied organic thermoelectric material, typically produce n-type materials that perform much worse than their p-type counterparts.

The fact that SWCNT thin films can make p-type and n-type legs out of the same material with identical performance means that the electrical current in each leg is inherently balanced, which should simplify the fabrication of a device.

The highest performing materials had performance metrics that exceed current state-of-the-art solution-processed semiconducting polymer organic thermoelectrics materials.

The research was funded by a cooperative research and development agreement (CRADA) with partner International Thermodyne. The fundamental research in SWCNT separation and optical/electrical characterization is supported by the U.S. Department of Energy's Office of Science.

"We could actually fabricate the device from a single material"


"In traditional thermoelectric materials you have to take one piece that's p-type and one piece that's n-type and then assemble those into a device."


Andrew Ferguson, NREL's Chemical and Materials Science and Technology center

Large n- and p-type thermoelectric power factors from doped semiconducting single-walled carbon nanotube thin films

Bradley A. MacLeod | Noah J. Stanton | Isaac E. Gould | Devin Wesenberg | Rachelle Ihly | Zbyslaw R. Owczarczyk | Katherine E. Hurst | Christopher S. Fewox | Christopher N. Folmar | Katherine Holman Hughes | Barry L. Zink | Jeffrey L. Blackburn | Andrew J. Ferguson

Abstract

Lightweight, robust, and flexible single-walled carbon nanotube (SWCNT) materials can be processed inexpensively using solution-based techniques, similar to other organic semiconductors. In contrast to many semiconducting polymers, semiconducting SWCNTs (s-SWCNTs) represent unique one-dimensional organic semiconductors with chemical and physical properties that facilitate equivalent transport of electrons and holes. These factors have driven increasing attention to employing s-SWCNTs for electronic and energy harvesting applications, including thermoelectric (TE) generators. Here we demonstrate a combination of ink chemistry, solid-state polymer removal, and charge-transfer doping strategies that enable unprecedented n-type and p-type TE power factors, in the range of 700 μW m−1 K−2 at 298 K for the same solution-processed highly enriched thin films containing 100% s-SWCNTs. We also demonstrate that the thermal conductivity appears to decrease with decreasing s-SWCNT diameter, leading to a peak material zT ≈ 0.12 for s-SWCNTs with diameters in the range of 1.0 nm. Our results indicate that the TE performance of s-SWCNT-only material systems is approaching that of traditional inorganic semiconductors, paving the way for these materials to be used as the primary components for efficient, all-organic TE generators.

www.nrel.gov    www.du.edu    www.ithermodyne.com   


About International Thermodyne

We are not a corporation, we are a team. We’re a mix of individuals who share a common vision. Our goal is to change the way the world perceives, captures and uses energy. We believe that we can power the world around us by creating unique devices that harvest energy from sources previously considered inert and converting that energy into electricity. This might mean objects as mundane as chairs, carpeting, walls, clothing, blankets, construction material or even your skin. Our team is here to help make that world a reality.

Source: International Thermodyne

About National Renewable Energy Laboratory (NREL)

NREL is the U.S. Department of Energy's primary national laboratory for renewable energy and energy efficiency research and development. NREL is operated for the Energy Department by The Alliance for Sustainable Energy, LLC.

Source: National Renewable Energy Laboratory (NREL)

About University of Denver

The University of Denver is a coeducational, four-year university in Denver, Colorado. Founded in 1864, it is the oldest independent private university in the Rocky Mountain Region of the United States

Source: University of Denver


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