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Transparent displays create new uses for windows

MUNICH, Germany — A team of Fraunhofer researchers is developing technologies that aim at making transparent screens usable as displays. Prototypes will be shown at the Hannover Industry Fair (April 20 through April 24).

Five Fraunhofer institutes have bundled their expertise to drive the research and development of transparent display technology. The researchers hope to enable designers to build devices that can be used as transparent windows as well as displays.

The core element of such displays is a conductive transparent coating. Currently, such coatings are too expensive to produce even small series in industrial manufacturing processes, and their electrical properties also are not yet optimized. In order to bring costs down and properties closer to industrial usability, the researchers pursuit two different approaches.

Approach number one is printing the conductive layer directly onto a substrate, for instance on glass. While there already exists a process, the sol-gel technique, that enables printing the material directly, the conductance of that coating is far too low to make it suitable for display purposes, explained project manager Peer Loebmann from Fraunhofer institute of surface technology (Fraunhofer ISC) in Wuerzburg.

According to Loebman, the research team that includes experts from the Fraunhofer institutes ISC, IST (Braunschweig), IWM and IPMS (both Dresden) and ISE (Freiburg) has already succeeded to increase the coating conductance by a factor of five, enough to enable display sol-gel-based applications. However, the upside potential still is enormous; conventional coatings, manufactured using lithography and etching, feature ten times higher conductance. In addition, printing processes are significantly faster than light exposure plus etching.

Approach number two is developing novel coating materials that create conductance on a different way compared to conventional materials. Typically, transparent layers feature n conductance which means that the current is based on the flow of electrons. The researchers aim at developing transparent p-conducting layers in which the current is based on the flow of defect electrons, or holes.

While these materials are characterized by lower conductance and worse transparency features compared to p conducting materials, they enable designers to create transparent active electronic elements such as transistors or solar cells by combining them with n-conductors.

In a first step, the researchers have created transparent conductors based on the sol-gel process. The work now focuses on improving the conductance. At the Hannover fair, the research group will display working prototypes of their achievements.

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