Coming soon: Hi-Bri OLEDs out of the inkjet printer?

July 10, 2019 //By Christoph Hammerschmidt
Coming soon: Hi-Bri OLEDs out of the inkjet printer?
Scientists have succeeded in using a new active principle to reduce the number of different layers in OLEDs to just one. In the future, this could enable organic LEDs that can be printed with an inkjet printer. The first prototype of the new OLEDs developed can already compete with current designs on the market in terms of efficiency and luminosity.

Organic light-emitting diodes are components that, in contrast to conventional LEDs, do not consist of compounds containing gallium, but of so-called organic compounds in which carbon is a major component. Compared to conventional light-emitting diodes, however, the luminosity and service life of OLEDs are currently even lower, which is why they represent a current field of research.

Scientists at the Max Planck Institute for Polymer Research (MPI-P) in Mainz (Germany) around Dr. Gert-Jan Wetzelaer have now developed a new OLED concept: OLEDs today consist of various wafer-thin layers. Some layers are used to transport charges, while others are used to efficiently inject electrons into the active layer where light is generated. Thus, conventional OLED displays easily reach a total of five to seven layers. The researchers have now developed an OLED that consists of a single layer that is powered by two electrodes. This simplifies the manufacture of OLEDs and paves the way for printable displays that don't have to hide behind current products when it comes to brightness.

The scientists use a light-emitting layer based on what is known as Thermally Activated Delayed Fluorescence (TADF). This physical principle has been known for several decades; it became the focus of OLED research only about ten years ago, when an efficient conversion of electrical energy into light was demonstrated in Japan. Since then, researchers have been working on the production of TADF-based OLEDs because they do not require expensive molecular complexes containing rare earth metals as used in today's OLEDs.

With their first prototype, the scientists were able to show that with a voltage of only 2.9 volts, their OLED can generate a brightness of emitted light of 10,000 candela / square meter - about 100 times the brightness of modern screens. Achieving such a high luminosity at this low voltage is a record for current OLEDs. The researchers were also able to measure an external efficiency of 19% - this is the percentage of the electrical energy supplied that is converted into light. With this value, the OLED prototype can compete with conventional multilayer OLEDs.

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