Single-layer OLED could be inkjet-printed

A new single layer OLED illuminates the logo for Max Planck Institute for Polymer Research. (MPI-P)

Polymer researchers have developed a more efficient Organic Light-Emitting Diode (OLED) for use in smartphone or TV displays that relies on just one layer instead of the several layers being used today. 

With just one layer, the light-emitting diodes could be printed with an inkjet printer in the future, according to researchers at the Max Planck Institute for Polymer Research in Mainz, Germany. Such an innovation would be valuable for industrial uses, greatly reducing OLED production costs.

Current OLEDs have several wafer-thin layers with some layers used to transport charges and other layers used to insert electrons into the active layer where light is generated. As a result, OLEDs can have five to seven layers. The MPI researchers developed an OLED with one layer that gets electricity via two electrodes.

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With the single-layer prototype, they were able to generate the brightness equal to 100 times the luminosity of modern screens with only 2.9 volts, a record. They were also able to reach an external efficiency of 19% which competes with OLEDs that have five or more layers. This efficiency rating is a measure of how much electricity is converted to the light that comes out in the direction of the viewer.

The prototype also has a lifetime of about 2000 hours of brightness that equals about 10 times of modern displays, but over that time period the initial luminosity dropped to half as much. “We hope to be able to improve the concept even further and achieve even longer lifetimes,” said Gert-Jan Wetzelaer of MPI in a statement. He led the group conducting the research.

OLED luminosity generally is not as good as more conventional LEDs which have been made of gallium, a semiconducting material. Instead, the organic component is mainly carbon. The MPI scientists used a light-emitting layer based on a process known as Thermally Activated Delayed Fluorescence in building their prototype, which doesn’t require using expensive rare-earth metals being used in current OLEDs.

The results are published in Nature Photonics.

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