By Josh Perry, Editor
[email protected]

Researchers from the Agency for Science, Technology, and Research (A*STAR) Institute of Materials Research and Engineering (IMRE) in Singapore are working to develop low-power thermoelectric generators that would convert waste heat, potentially including body heat, into electricity to keep wearable devices operating.

The development of efficient thermoelectric materials means that body-heat alone from, say, a person’s hand, can be used to power small portable devices, in this case a red LED.
(A*STAR Institute of Materials Research and Engineering)

According to a report from A*STAR, the PHAROS project began in 2016 with the idea of creating thermoelectric generators to power Internet of Things (IoT) devices, medical wearables, and even to reuse waste heat from vehicles to lower their carbon footprint.

The goal of the project is to find new thermoelectric materials, moving away from metal tellurides that are only effective at high temperatures. The researchers have studied several semiconducting polymers as possible organic components in hybrid thermoelectric generators. These polymers would be combined with tellurium nanowires, silicon nanoparticles, or other inorganic materials.

Researchers created a ZT value to more easily compare different materials. The value incorporates the material’s Seebeck coefficient, thermal conductivity, electrical conductivity, and temperature.

A breakthrough came in collaboration with the Lawrence Berkeley National Laboratory (Berkeley, Calif.). The scientists found a specially-designed, conjugated polymer combined with tellurium nanowires that comes close to the “perfect” ZT value of 1.0. Researchers were also able to detail how charge flows in these materials to boost future studies.

“A material with a ZT of 1 operating with a temperature difference of roughly 10?C at room temperature generates roughly 50 microwatts per square centimeter, and, in theory, PHAROS's most recent material could achieve 10 microwatts per square centimeter,” the report explained. “So, small-scale wearable thermoelectric power is already tantalizingly close to reality.”

The polymer research was recently published online. The abstract stated:

“Hybrid (organic-inorganic) materials have emerged as a promising class of thermoelectric materials, achieving power factors exceeding those of either constituent. The mechanism of this enhancement is still under debate, and pinpointing the underlying physics has proven difficult.

“In this work, we combine transport measurements with theoretical simulations and first principles calculations on a prototypical PEDOT:PSS-Te(Cux) nanowire hybrid material system to understand the effect of templating and charge redistribution on the thermoelectric performance.

“Further, we apply the recently developed Kang-Snyder charge transport model to show that scattering of holes in the hybrid system, defined by the energy-dependent scattering parameter, remains the same as in the host polymer matrix; performance is instead dictated by polymer morphology manifested in an energy-independent transport coefficient.

“We build upon this language to explain thermoelectric behavior in a variety of PEDOT and P3HT based hybrids acting as a guide for future work in multiphase materials.”