German researchers claim first transparent OLED pixels

If you've seen the movie "Minority Report" and marveled at the transparent computer screens used by Tom Cruise, you'll appreciate what German researchers have concocted in their labs: entirely transparent OLED (organic light emitting diode) pixels.

The researchers, located at the Technical University of Braunschweig, are claiming the development to be a world's first.

Their approach is to use transparent TFTs (thin-film transistors) made of a 100-nanometer-thick layer of zinc-tin-oxide, which transmits more than 90 percent of visible light. Such transistors are more often made of silicon, which is used for LCDs (liquid crystal displays) but is highly absorptive in the visible part of the spectrum.

In the transparent displays, the TFTs and the OLED pixels are positioned next to each other. The OLED pixel can be placed on top of the TFT driver circuit without interference.

In addition, because the TFT layers are thin, they can be deposited on large areas with conventional techniques, and because these techniques can be performed at temperatures below 200 degrees Celsius, cheap, flexible plastic substrates can be used.

In the devices developed by the researchers, the brightness of the OLED pixels varied from 0 to 700 candelas per square meter by changing the voltage of the driving TFTs. By comparison, typical computer screens today reach a brightness of approximately 300 candelas per square meter.

Thomas Riedl, head of the organic and inorganic lasers team of the High-Frequency Institute at the Technical University of Braunschweig expects the first prototype transparent OLED displays to be available in two years.

Transparent displays could have numerous applications, including screens that supply surgeons with additional information in their field of view or car windscreens that allow drivers to view instructions while driving, according to Riedl.