Stable electrodes, easy to assemble highly conductive fibers could give thinner and printable flexible electronics

One of the cutting edge technologies currently used in manufacturing allows for printing materials directly onto a surface to create electrically functioning devices which are very thin and flexible. The best example of such an application are organic light-emitting diodes (OLEDs), widely used as displays for most new generation smart phones commercially available today. The process however is very tedious, and the resulting devices become vulnerable to outside chemical phenomena, thus the need for an extra isolating casing, which makes the process expensive and the resulting device thicker. Typically, printed electronics, an industry set to grow by tens of billions of dollars over the next 10 years, creates light or energy ultimately needed to display information on a screen by injecting or collecting electrons. Current technology employs conductors like calcium, magnesium or lithium, which are highly chemically reactive materials. When exposed to oxygen or humidity, these metals oxidize and cease to function, so for the printed electronics to stably work they must be covered with a rigid, thick barrier such as glass or expensive encapsulation layers. Scientists have sought to replace these materials with ones that can work exposed to ambient conditions; however the ones currently in use have been deemed the best options because of their low-work function, the prime prerequisite for workable printed electronics. The work function is the minimum energy needed to remove an electron from a solid to a point immediately outside the solid surface. A team of researchers led by Georgia Tech's Bernard Kippelen has developed the first completely plastic solar cell. To demonstrate their research�s findings, the Georgia Tech scientists built the first-ever, completely plastic solar cell and also evaluated the polymers� performance in organic thin-film transistors and OLEDs. They may have introduced a printed electronics atypical conductor with a low-work function by applying thin layer of polymer coating on the conductor�s surface. This makes it safe for use in ambient conditions, as well as efficient. The scientists managed to reduce the work function of a conductor by applying a very thin layer of a polymer, approximately 1-10 nanometers thick, to its surface to create a strong surface dipole. This interaction dramatically lowers the work function of conductors, which function without any issues exposed to air, but which couldn�t have been used in printable electronics until now. Best of all, the technique is universal and totally inexpensive, making use of polymers already commercially available. �These polymers are inexpensive, environmentally friendly and compatible with existent roll-to-roll mass production techniques,� said Bernard Kippelen, director of Georgia Tech�s Center for Organic Photonics and Electronics (COPE). �Replacing the reactive metals with stable conductors, including conducting polymers, completely changes the requirements of how electronics are manufactured and protected. Their use can pave the way for lower cost and more flexible devices.�
In another development, French researchers have produced highly conductive plastic fibers with a thickness of only a few nanometers that self-assemble when exposed to a flash of light. The tiny fibers (1 nanometer equals one billionth of a meter) could become a cheaper and easier-to-handle alternative to carbon nanotubes and play a role in the development of electronic components on the nanoscale. As per www2.cnrs.fr, researchers from the Centre National de la Recherche Scientifique (CNRS), an organization funded by the French government, and the Universit� de Strasbourg say the fibers combine the properties of metals and plastic organic polymers, which are commonly used to conduct electric current, and see applications in several fields ranging from electronics to architecture. Lead researchers Nicolas Giuseppone and Bernard Doudin want to demonstrate that the plastic fibers have the potential to be integrated into products such as flexible screens and solar cells. In the latest research, the molecules were placed in contact with an electronic microcircuit comprising gold electrodes spaced 100 nm apart then applied an electric field between these electrodes. Not only were the fibers were found to self-assemble between the electrodes when triggered by a flash of light, but they are also able to transport current densities approaching that of copper wire. These light and flexible "supramolecular� structures also have very low interface resistance with metals, or 10,000 times below that of the best organic polymers. �It is difficult to know if the current technologies can incorporate them readily or if we need to change the surrounding devices to adapt these new structures,� Giuseppone told Gizmag. �We are currently trying an insertion in current technologies to improve them, but maybe these fibers are sufficiently novel to enable new technologies. This would be, in fact, the most interesting for us.� Giuseppone points out that the race to miniaturize electronic components on the nano scale requires �extremely efficient active components with, for instance, very low interface resistance between the components of the electronic circuits." These fibres show such behavior. Another advantage of the self-constructing attributes of the fibers is that they enable the adoption of a "bottom-up" manufacturing approach, potentially making processing easier, faster and cheaper.