Printed designer organic electronics

June 17, 2015 // By Jean-Pierre Joosting
Printed microelectronic components made of synthetics offer the benefits of being thin, light-weight, flexible and can be produced cost- and energy-efficiently. Some applications include flexible displays and touch screens, glowing films, RFID tags and solar cells.

As an alternative to classical silicon technology, organic electronics offer a promising future. Today, flexible monitors and glowing wall paper made of organic light emitting diodes, so-called OLEDs, are in rapid development.

Part of an international project, physicists at the Technische Universität München (TUM) have now documented the creation of razor thin polymer electrodes during the printing process and successfully improved the electrical properties of the printed films.

However, to manufacture the components on an industrial scale, semiconducting or insulating layers — each a thousand times thinner than a human hair — must be printed onto a carrier film in a predefined order. "This is a highly complex process, whose details need to be fully understood to allow custom-tailored applications," explains Professor Peter Müller-Buschbaum of the Chair of Functional Materials at TU München.

A further challenge is the contacting between flexible, conducting layers. Typically, electronic contacts made of crystalline indium tin oxide are frequently used. However, this construction has numerous drawbacks: The oxide is more brittle than the polymer layers over them, which limits the flexibility of the cells. Furthermore, the manufacturing process also consumes much energy. Finally, indium is a rare element that exists only in very limited quantities.

A few months ago, researchers from the Lawrence Berkeley National Laboratory in California for the first time succeeded in observing the cross-linking of polymer molecules in the active layer of an organic solar cell during the printing process. In collaboration with their colleagues in California, Müller-Buschbaum's team took advantage of this technology to improve the characteristics of the polymer electronic elements.

Organic electronics, based on conducting polymers, are hailed as a promising future market. This is the cover illustration of Advanced Materials (10.1002/adma.201570148). Image courtesy of Christoph Hohmann, Nanosystems Initiative Munich.