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Better organic compound developed for thermoelectric devices PDF Imprimer Envoyer
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Lundi, 27 Mai 2013 10:41

By mixing two polymers used in L.E.D.s and solar cells, researchers from the University of Michigan have developed a better thermoelectric material.Thermoelectric materials can turn heat into electricity and are being looked at as a way to harness waste heat from industrial processes or even automobiles as a source of power.

Most efficient thermoelectric materials are made of rare inorganic semiconductors such as bismuth, tellurium and selenium. Because these substances are rare, they are also expensive. They also have a tendency to be brittle and toxic, making them hard to dispose of.

The U-M researchers worked with organic semiconductors, carbon-rich compounds that are relatively cheap, abundant, lightweight and tough.

Specifically, they combined a mixture of two organic polymers: the conjugated polymer PEDOT and the polyelectrolyte PSS. This creates the compound known as PEDOT: PSS, which has been used as a transparent electrode for devices such as organic L.E.D.s and solar cells.

While the U-M scientists were not the first to theorize organic semiconductors such as PEDOT: PSS could be used in thermoelectric devices, previous efforts have not been very efficient.

The efficiency of thermoelectric materials – how well they convert heat to electricity – is measured as the thermoelectric “figure of merit.” This metric is around 1 near room temperature for the best inorganic thermoelectric materials but only 0.25 for organic ones.

U-M was able to improve PEDOT: PSS’s metric by nearly 70 percent, for a figure-of-merit of 0.42.

Previous work with organic thermoelectronics sought to increase their capacity to conduct electricity by adding impurities through a process known as doping. When the dopants bond with a material, they give it an additional electrical carrier and increase the materials conductivity.

In PEDOT doped by PSS, however, only a small percent of the PSS molecules bond with the PEDOT. The excess PSS molecules push the PEDOT molecules further apart and inhibit the electroconductivity and thermoelectric performance of the material.

The U-M researchers used solvents to remove some of the excess PSS leading to large increases in both the electrical conductivity and thermoelectric energy conversion efficiency. Their organic thermoelectric material can efficiently convert heat to energy at temperatures up to 250 degrees Fahrenheit.

The work was part of the Center for Solar and Thermal Energy Conversion, an Energy Frontier Research Center funded by the U.S. Department of Energy Office of Science, Office of Basic Energy Sciences. 

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Mise à jour le Lundi, 27 Mai 2013 10:58


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