Ink enables electronics to be printed on flexible substrates

Illinois University materials scientists have developed a reactive silver ink for printing high-performance electronics on materials, including flexible plastic, paper or fabric substrates.

According to a statement, electronics printed on low-cost, flexible materials hold promise for antennas, batteries, sensors, solar energy or wearable devices.

Most conductive inks rely on metal particles suspended in the ink. The new ink is a transparent solution of silver acetate and ammonia: the silver remains dissolved in the solution until it is printed and the liquid evaporates, yielding conductive features.

‘It dries and reacts quickly, which allows us to immediately deposit silver as we print,’ said graduate student S Brett Walker.

The reactive ink is said to have several advantages over particle-based inks. It is much faster to make, with a batch taking minutes to mix, according to Walker, whereas particle-based inks take several hours and multiple steps to prepare. The ink is also stable for several weeks.

The reactive silver ink also can print through 100nm nozzles, which is claimed to be an order of magnitude smaller than particle-based inks. Moreover, the ink’s low viscosity makes it suitable for inkjet printing, direct ink writing or airbrush spraying over large, conformal areas.

‘For printed electronics applications, you need to be able to store the ink for several months because silver is expensive,’ said Walker. ‘Since silver particles don’t actually form until the ink exits the nozzle and the ammonia evaporates, our ink remains stable for very long periods. For fine-scale nozzle printing, that’s a rarity.’

The reactive silver ink can also be processed at low temperatures. Metallic inks typically need to be heated to achieve bulk conductivity through annealing. The annealing temperatures for many particle-based inks are too high for some inexpensive plastics or paper. By contrast, the reactive silver ink exhibits an electrical conductivity approaching that of pure silver upon annealing at 90ºC.

‘We are now focused on patterning large-area transparent conductive surfaces using this reactive ink,’ said Jennifer Lewis, the Hans Thurnauer professor of materials science and engineering at the university.

Lewis and Walker described the new ink in the Journal of the American Chemical Society.