25 January 2012
Materials scientists at the University of Illinois at Urbana-Champaign (UIUC) developed a reactive silver ink for printing small, high-performance electronics that readily allow light to pass through the patterned surfaces, making the breakthrough product attractive for solar applications.
Jennifer Lewis, Hans Thurnauer Professor of Materials Science and Engineering and her research group at UIUC are particularly pleased with their new silver ink’s “wide applicability and excellent electrical properties,” according to the University’s news bureau. The new discovery opens the door for a group of inexpensive materials that could not be used for printed microelectronics with conventional, particle-based conductive inks. “This particle-free silver ink is capable of being patterned through very fine nozzles—100 nm in diameter—to create linewidths as small as five microns,” Lewis explains. “Because it exhibits bulk silver conductivity upon heating at 90 degrees Celsius for 15 minutes, it is highly compatible with a broad range of materials, including molecular organics and plastics.” The low processing temperature, approaching that of pure silver, is a key feature regarding the new ink’s usefulness, as the annealing temperatures for many particle-based inks are too high for inexpensive plastics or paper.
The new silver ink and its associated never-before-seen fine-scale nozzle printing capabilities hold promise for the evolution of solar energy. “We think the main application will be in printing transparent conductive microgrids that readily allow light to pass through the patterned surfaces,” Lewis says.
While most conductive inks rely on tiny metal particles suspended in the ink, the relevant innovation with this new ink is that it is a transparent solution of silver acetate and ammonia. The silver remains dissolved in the solution until it is printed. Upon printing, the liquid component quickly evaporates, leaving behind finest lines of dry, conductive silver. Additional advantages of this new kind of reactive, low-viscosity ink include that a batch is mixed in minutes, whereas particle-based inks take several hours and multiple steps to prepare. The ink also is stable for several weeks, so it does not have to be used right away.
Asked about patterning techniques that could potentially be used in solar applications, Lewis says, “Our particle-free silver ink can be used with several patterning approaches, including direct ink writing, inkjet printing, aerosol jet printing and airbrush spraying for large areas. We are primarily focused on ink printing approaches.”