In even the most fuel-efficient cars, about 60 percent of the total energy of gasoline is lost through heat in the exhaust pipe and radiator. To combat this, researchers are developing new thermoelectic materials that can convert heat into electricity. These semiconducting materials could recirculate electricity back into the vehicle and improve fuel efficiency by up to 5 percent.

The challenge is, current thermoelectric materials for waste heat recovery are very expensive and time consuming to develop. One of the state of the art materials, made from a combination of hafnium and zirconium (elements most commonly used in nuclear reactors), took 15 years from its initial discovery to optimized performance.

Now, researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have developed an algorithm that can discover and optimize these materials in a matter of months, relying on solving quantum mechanical equations, without any experimental input.

“These thermoelectric systems are very complicated,” said Boris Kozinsky, a recently appointed Associate Professor of Computational Materials Science at SEAS and senior author of the paper. “Semiconducting materials need to have very specific properties to work in this system, including high electrical conductivity, high thermopower, and low thermal conductivity, so that all that heat gets converted into electricity. Our goal was to find a new material that satisfies all the important properties for thermoelectric conversion while at the same time being stable and cheap.”

Kozinsky co-authored the research with Georgy Samsonidze, a research engineer at the Robert Bosch Research and Technology Center in Cambridge, MA, where both authors conducted most of the research.

In order to find such a material, the team developed an algorithm that can predict electronic transport properties of a material based only on the chemical elements used in the crystalline crystal. The key was to simplify the computational approach for electron-phonon scattering and to speed it up by about 10,000 times, compared to existing algorithms.

The new method and computational screening results are published in Advanced Energy Materials.

Using the improved algorithm, the researchers screened many possible crystal structures, including structures that had never been synthesized before. From those, Kozinsky and Samsonidze whittled the list down to several interesting candidates. Of those candidates, the researchers did further computational optimization and sent the top performers to the experimental team.

In an earlier effort experimentalists synthesized the top candidates suggested by these computations and found a material that was as efficient and as stable as previous thermoelectric materials but 10 times cheaper. The total time from initial screening to working devices: 15 months.

“We did in 15 months of computation and experimentation what took 15 years for previous materials to be optimized,” said Kozinsky. “What’s really exciting is that we’re probably not fully understanding the extent of the simplification yet. We could potentially make this method even faster and cheaper.”

Kozinsky said he hopes to improve the new methodology and use it to explore electronic transport in a wider class of new exotic materials such as topological insulators.

Cheap, flexible and sustainable plastic semiconductors will soon be a reality thanks to a breakthrough by chemists at the University of Waterloo.

Professor Derek Schipper and his team at Waterloo have developed a way to make conjugated polymers, plastics that conduct electricity like metals, using a simple dehydration reaction the only byproduct of which is water.

“Nature has been using this reaction for billions of years and industry more than a hundred,” said Schipper, a professor of Chemistry and a Canada Research Chair in Organic Material Synthesis. “It’s one of the cheapest and most environmentally friendly reactions for producing plastics.”

Schipper and his team have successfully applied this reaction to create poly(hetero)arenes, one of the most studied classes of conjugated polymers which have been used to make lightweight, low- cost electronics such as solar cells, LED displays, and chemical and biochemical sensors.

Dehydration is a common method to make polymers, a chain of repeating molecules or monomers that link up like a train. Nature uses the dehydration reaction to make complex sugars from glucose, as well as proteins and other biological building blocks such as cellulose. Plastics manufacturers use it to make everything from nylon to polyester, cheaply and in mind-boggling bulk.

“Synthesis has been a long-standing problem in this field,” said Schipper. “A dehydration method such as ours will streamline the entire process from discovery of new derivatives to commercial product development. Better still, the reaction proceeds relatively fast and at room temperature.”

Conjugated polymers were first discovered by Alan Heeger, Alan McDonald, and Hideki Shirakawa in the late 1970s, eventually earning them the Nobel Prize in Chemistry in 2000.

Researchers and engineers quickly discovered several new polymer classes with plenty of commercial applications, including a semiconducting version of the material; but progress has stalled in reaching markets in large part because conjugated polymers are so hard to make. The multi-step reactions often involve expensive catalysts and produce environmentally harmful waste products.

Schipper and his team are continuing to perfect the technique while also working on developing dehydration synthesis methods for other classes of conjugated polymers. The results of their research so far appeared recently in the journal Chemistry – A European Journal.