Cheap, Efficient Printed Electronic Devices

Powerful X-rays that can see down to the molecular level of organic materials used in printable electronics have revealed in new detail how to achieve high-performance transistors and solar cells with polymers—and why some materials perform better than others. These findings could lead to cheaper, more efficient printable electronic devices, according to a team of researchers at UC Santa Barbara.

Published in the journal Nature Materials, “This work is exciting because it helps reveal in new detail how we can achieve high performance transistors and solar cells with polymers,” explained UC Santa Barbara professor of materials Michael Chabinyc, who, with UCSB chemistry graduate student Justin Cochran and North Carolina State physicists Harald Ade and Brian Collins, set out to find out which materials and which processing steps worked better, in what is still a largely trial-and-error process for manufacturers of printable electronics. The effort also involved collaboration with an international team, including researchers from Monash University in Australia and Univeristät Erlangen-Nümberg in Germany.

Until recently, the process of selecting the organic conductive molecules to be deposited onto surfaces and what steps to take in order to improve their performance was something of a mystery as some materials and treatments worked better than others. “In transistors, we found that as the alignment between molecules increased, so did the performance,” Collins said. “In the case of the solar cells, we discovered alignment of molecules at interfaces in the device, which may be the key to more efficient harvesting of light. For both, this was the first time anyone had been able to really look at what was happening at the molecular level.”

The researchers said they hope this new technique will provide a better perspective into the nature of organic materials used in printed electronics and give researchers and manufacturers greater insight into the fundamentals of these materials since understanding how these materials work can only lead to improved performance and better commercial viability.

Continuing Moore’s Law With Multiblock Polymers?

In a move that seems like it could allow Moore’s Law to continue scaling, Intel is partnering with researchers also at UC Santa Barbara to develop multiblock polymers that will enable patterning of microelectronic devices at finer scales and lower cost.

With advances in polymer chemistry and a wide variety of monomer constituents to choose from, the world of multiblock polymers is wide open as these polymers can result in an astonishing array of materials, customizable to almost any specification, according to UC Santa Barbara scientists Glenn Fredrickson and Kris Delaney. However, the researchers caution that the flood of options could be overwhelming without a theoretical framework to guide research. Their paper, “Multiblock Polymers: Panacea or Pandora’s Box?” appears in the latest edition of the journal Science.

Polymers are large molecules comprised of repeating sequences of monomers. When more than one monomer type is present and the dissimilar monomers are organized and chemically bound into blocks, the resulting multiblock polymers can serve as the basis for a multitude of materials, to be used in applications as diverse as tennis shoes and solar cells. Scientists can create materials using monomers from a variety of sources, from petroleum to renewable feedstocks such as sugar or cellulose.

Multiblock copolymers can self-assemble into nanometer-sized domains, and therefore can exhibit remarkable combinations of properties, such as soft, strong, and elastic –– as in tennis shoe soles or skateboard wheels. For higher-tech applications, multiblock polymers could enable patterning of microelectronic devices at finer scales and lower cost.

The problem has become the sheer number of possible combinations for these monomers so the researchers suggest an approach that addresses materials performance needs by combining predictive computer simulation methods with advanced synthetic and structural characterization tools.

“Our simulation methods for predicting the self-assembled structures of multiblock polymers are quite advanced, and we are getting better at relating those nano-structures to the properties of the material. Multiblock polymers are extremely versatile—there is enormous latitude of design freedom, and it’s very promising in terms of developing materials with truly unique properties,” Fredrickson added.

The research team also included scientists from the University of Minnesota and the University of Texas.

—Ann Steffora Mutschler