PORTLAND, Ore. Organic conductors, semiconductors and insulators were ink-jet printed onto an expensive polymer substrate to demonstrate all-plastic transistors that could slash the price of organic solar cells, according to researchers at Princeton University. Professor Yueh-Lin (Lynn) Loo invented a new plasticizing process for her all-plastic transistors that she hopes will obsolete the use of rare and expensive indium-tin-oxide (ITO) in solar cells.
"We have discovered the mechanism that makes conductive polymers lose much of their conductivity when they are made soluble for ink-jet printing," said Loo. "By post-processing a circuit after ink-jet printing, we can now recover the lost conductivitymaking these organic materials a good substitute for the ITO used in solar cells today."
Conductive polymers have been known for over a decade, but until now dissolving them in a solvent so they could be ink-jet printable also caused their conductivity to drop by up to 1,000 times. Loo's research team discovered that by post-processing ink-jet printed plastic electronics with a special acid, the polymer's internal bonds can be relaxed back to the state they were in before printing, thereby recovering their conducting properties. Similar to the plasticizing process that makes hard plastics softer, Loo's technique regains the loss incurred when conductive polymers are dissolved in a solvent for ink-jet printing.
|Princeton researchers have developed a plastic process for ink-jet printing conductive polymers shown here in a plastic transistor with interdigitated source and drain (orange) allowing current flow down the active channel (green). Image courtesy of Loo Research Group.|
The technique can be adapted immediately to substitute for the ITO used in solar cells, according to Loo. With further development, the technique could also be used for other ink-jet printable electronic applications such as all-plastic large area displays and medical diagnostic devices, Loo said.
Funding for the project was provided by the National Science Foundation, the W.M. Keck Foundation and the Arnold and Mabel Beckman Foundation.