Polymer Alignment Speeds Conductivity

In most universes and dimensions, the shortest distance between two points is a straight line.

This statement is true in the electronic realm as well. Now, researchers at the University of Michigan have aligned molecules of semiconducting polymers sopolymer semiconductor that electricity can flow more easily.

The innovation could create a breakthrough for computer processors, LED displays, and solar cells. The advance could mean that electronics will be cheaper and greener, reports Discovery News.

Semiconductors are the key pieces for our electronics. Inorganic semiconductors are expensive and require high temperatures for their manufacture. Organic and plastic semiconductors, on the other hand, can be made at room temperature in a well-equipped laboratory.

The problem with that, however, is that electricity cannot move through plastics as well as it can through semiconductors, reports e! Science News. In part, that is because each semiconducting polymer molecule is like a randomly arranged wire — called a charge mobility — that creates a lot of detours for the electricity to travel.

“Along the polymer backbones are these one-dimensional wires. The charge mobility is relatively fast along the backbone,” says Jinsang Kim, professor of materials science and engineering who led the research at the university. “But between the polymer backbones, the charge carriers hop and the charge mobility is much smaller.”

For the researchers, trying to get the polymers aligned was a lot like arranging nanoscopic linguine into orderly lines. e! Science News explains further how they did it:

Kim’s group approached the problem by making smarter semiconducting polymers. They wanted a liquid polymer solution they could brush over a surface, and the molecules would automatically align with one another in the direction of the stroke, assembling into high-performance semiconducting thin-layer films.

First, they designed the polymers to be slippery — ordinary polymers glom together like flat noodles left in the fridge, Kim said. By choosing polymers with a natural twist, the team kept them from sticking to one another in the solution. But in order to align during the brushstroke, the polymers needed to subtly attract one another. Flat surfaces would do that, so the team designed their polymer to untwist as the solvent dried up.

The researchers found that these polymers lined up in the direction of an applied force, like from a tug of a paintbrush. They could spread the polymer over surfaces, such as glass or flexible plastic film. That material then could be put into a simple transistor, a component of computer processors.

The alignment helped the electricity move 1,000 times faster. Kim says:

By combining the established molecular design principle with a polymer that has a very good intrinsic charge carrier mobility, we believe it will make a huge difference in organic electronics. We are currently developing a versatile fabrication method in order to realize high-performance and paintable plastic electronics in various length scales from nanometers to meters.

The research team believes that the innovation could replace the polymer “ink” in nanoscale pens that etch circuits and improve the liquid coating of electronic components built into LED displays or solar panels. “In terms of commercial application, its potential is unlimited,” says Bong-Gin Kim, a lead author of the paper on the research that was published in Nature Materials. “The final target of this alignable polymer could be a paintable, printable electric circuit in the future.”

Source: “Paint-On Plastic Electronics to Bring Down Cost,” Discovery News, 3/25/13
Source: “Paint-on plastic electronics: Aligning polymers for high performance,” e! Science News, 3/25/13
Image by Joseph Xu, Communications & Marketing, College of Engineering, University of Michigan, used with permission.