Larger OLED Displays
Nanostructured metals could replace expensive and brittle oxide-based transparent electrode materials for use in displays

Source: “Nanoimprinted Semi­transparent Metal Electrodes and Their Application in Organic Light-Emitting Diodes”
Myung-Gyu Kang and L. Jay Guo
Advanced Materials online, April 13, 2007

Results: University of Michigan researchers have made flexible grids of copper, gold, and aluminum that are almost transparent, so thin and distantly spaced are their wires. The wires are 120 or 200 nano­meters wide and separated by gaps of about 500 nanometers in one direction and 10 micrometers in the other. Used as electrodes, the grids outperformed the indium tin oxide (ITO) electrodes commonly used in displays and ­photovoltaics.

Why it matters: The grids could be particularly useful for organic light-emitting diodes (OLEDs), which make displays that are bright, efficient, and potentially flexible. OLEDs are now limited to use in small displays, such as those in mobile phones. ITO is too brittle for use in larger flexible displays. The metal grids are not brittle and have better electrical properties than ITO.

Methods: The researchers used a technique called nanoimprint lithography to achieve the precise wire width and spacing necessary for the grids, testing different wire configu­rations for their transparency and their electronic properties. They also tested a prototype OLED that used a copper-grid electrode instead of an ITO one.

Next Steps: The proportions of the wires are being optimized to help the grids compete with other potential replacements for ITO, such as films made of carbon nanotubes.