Paint-on plastic electronics: Aligning polymers for high performance

Semiconductors are the key ingredient for computer processors, solar cells and LED displays, but they are expensive. Inorganic semiconductors like silicon require high temperatures in excess of 2,000 degrees Fahrenheit and costly vacuum systems for processing into electronics, but organic and plastic semiconductors can be prepared on a basic lab bench. The trouble is that charge carriers, like electrons, can't move through plastics nearly as easily as they can move through inorganic semiconductors. Part of the reason for this is because each semiconducting polymer molecule is like a short wire, and these wires are randomly arranged.
Jinsang 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. The team made molecules that matched their design and built a device for spreading the polymer solution over surfaces such as glass or a flexible plastic film. The force from the silicon blade, moving at a constant speed across the liquid polymer, was enough to align the molecules. The team then built the semiconducting film into a simple transistor, a version of the electronic components that make up computer processors (News Item University of Michigan, 24 March 2013).