Self-organized organic electronic and photonic materials by micro-dewetting

Abstract

Techniques based on rupture of a thin liquid film to form droplets and line structures create submicrometer-size patterns that are used in making organic LEDs and field-effect transistors. Many electronic and photonic devices require patterning of some of the materials involved. There are three main challenges in this field: decreasing pattern size, increasing throughput, and lowering production cost and energy. The first task is tackled by top-down light-and electron-beam lithographies, as well as bottom-up biomimetic methods using, for example, DNA and protein templates. As a result, pattern sizes are now down to a few nanometers. However, the direct-writing techniques necessary for the highest resolution are very time-consuming, with typical writing speeds of a few tens of micrometers per second. This drawback can be partially resolved by lithographically produced nanoimprint molds that allow roll-to-roll patterning and thus massively parallel production. Still, this approach suffers from technological hurdles, such as requiring complex steppers and lasers. Increasing throughput and reducing cost can also be achieved through solution processes. But the surface tension of liquids does not allow formation of arbitrarily small droplets. Only recently was it reported that a liquid printing process could break the micrometer barrier. 1, 2 Moreover, ink-jet printing is a serial process. Even though arrays of printing heads can be used, it still takes time to prepare large-area patterns. But surface tension does not pose only problems. The very fact that a liquid film or jet contracts and forms droplets can, in principle, be used to make a pattern. If a homogeneous liquid is placed on an unstructured substrate and the liquid breaks up into droplets, a pattern may form where no pattern existed before. Ilya Prigogine was a pioneer in the field of nonequilibrium dynamics and dissipative structures. 3 In applying his theory