materials science

Organic semiconductors on fast track

STANFORD (US) — Researchers have created a new material for high-speed organic semiconductors in a way that may shorten the development timeline by months, if not years.

Up until now, organic semiconductors have held immense promise for use in thin film and flexible displays—imagine an iPad that can be rolled up—but had not reached the speeds needed to drive high definition displays. Inorganic materials such as silicon are fast and durable, but don’t bend.

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For the most part, developing a new organic electronic material has been a time-intensive, somewhat hit-or-miss process, requiring researchers to synthesize large numbers of candidate materials and then test them.

The new research, reported in Nature Communications, scientists decided to try a computational predictive approach to substantially narrow the field of candidates before expending the time and energy to make any of them.

“Synthesizing some of these compounds can take years,” says Anatoliy Sokolov, postdoctoral researcher working in the lab of Zhenan Bao, associate professor of chemical engineering at Stanford University. “It is not a simple thing to do.”

The researchers used a material known as DNTT, already known to be a good organic semiconductor, as their starting point, then considered various compounds possessing chemical and electrical properties that seemed likely to enhance the parent material’s performance if they were attached.

They came up with seven promising candidates.

Semiconductors are all about moving an electrical charge from one place to another as fast as possible.  How well a material performs that task is determined by how easy it is for a charge to hop onto the material and how easily that charge can move from one molecule to another within the material.

Using the expected chemical and structural properties of the modified materials, researchers from Harvard University predicted that two of the seven candidates would most readily accept a charge.  They calculated that one of those two was markedly faster in passing that charge from molecule to molecule, so that became their choice. From their analysis, they expected the new material to be about twice as fast as its parent.

It took about a year and a half to perfect the synthesis of the new compound and make enough of it to test, Sokolov says.

“Our final yield from what we produced was something like 3 percent usable material and then we still had to purify it.”

When the the final product was tested, the predictions were borne out. The modified material doubled the speed of the parent material.  For comparison, the new material is more than 30 times faster than the amorphous silicon currently used for liquid crystal displays in products such as flat panel televisions and computer monitors.

“It would have taken several years to both synthesize and characterize all the seven candidate compounds. With this approach, we were able to focus on the most promising candidate with the best performance, as predicted by theory,” Bao says.
“This is a rare example of truly rational design of new high performance materials.”

The researchers hope their predictive approach can serve as a blueprint for other research groups working to find a better material for organic semiconductors.
And they’re eager to apply their method to the development of new, high-efficiency material for organic solar cells.

“In the case of renewable energy, we have no time for synthesizing all the possible candidates, we need theory to complement synthetic approaches to accelerate materials discovery,” says Alán Aspuru-Guzik, associate professor of chemistry and chemical biology at Harvard.

The research was supported financially by the Stanford Global Climate and Energy Project, Netherlands Organization for Scientific Research, National Science Foundation, King Abdullah University of Science and Technology, Air Force Office of Scientific Research, Harvard Materials Research Science and Engineering Center, the Camille & Henry Dreyfus Foundation and the Sloan Foundation.

More news from Stanford University: http://news.stanford.edu/

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