Imperial College in London has invented techniques for mass-producing solution-processed organic semiconductors on flexible substrates, and has won £250,000 to develop manufacturing prototypes.
“It would be really nice to do photolithography on large areas of organic semiconductor,” researcher John De Mello told EW. “It would be much faster than ink jet printing, for example.”
The problem with lithography is not the optical projection, said De Mello, but the etching phase after exposure. “Etchants ruin the remaining organic material,” he said.
The first Imperial technique involves turning conventional photolithography on its head. “We place the photo resist on the substrate then lay down the organic material,” said De Mello.
Following this, the resist is patterned optically, then ‘developed’ in a bath which dissolves the unwanted resist through the organic layer, causing waste organic material to detach and allowing it to be washed away. Patterning down to one micron has been achieved.
As a resist layer remains under the organic device, this technique is best suited to single layer devices, such as solar cells and OLEDs. “That said, it can be adapted to certain kinds of double layer devices,” said De Mello, “and we have extended it to lay down adjacent coloured pixels of a red-green-blue display.”
The second technique is solid-phase stamping, where a layer of organic material is patterned separately, then pushed - ‘stamped’ - on to a substrate.
Multiple layer devices are formed by stacking these solid layers. “There is quite a lot of subtlety with how you transfer a layer from a carrier to the substrate,” said De Mello.
The cash comes from the Royal Society’s annual £250,000 Brian Mercer Award for innovation in the field of nanotechnology.
“It will allow both processes to be adapted to reel-to-reel from the manual processes used in research,” said De Mello. “it is essentially two years’ funding and by the end we should have prototype machines for both.”