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On the way of printable organic electroluminescent diodes

On the way of printable organic electroluminescent diodes

The first OLED prototype developed in Mainz, Germany, illuminates the MPI-P logo. Credit: MPI-P

Organic light-emitting diodes are components that no longer consist of compounds containing gallium, a semiconductor material, but so-called organic compounds in which carbon is a main component. However, compared to conventional light-emitting diodes, the luminosity and lifetime of OLEDs are currently lower, which is why they are a current area of ​​research.

MPI-P scientists led by the group leader, Dr. Gert-Jan Wetzelaer (Professor Paul Blom's department), have come up with a new OLED concept. Today, OLEDs consist of various thin layers. Some layers are used to carry charges, while others are used to efficiently introduce electrons into the active layer in which light is generated. Thus, current OLEDs can easily consist of five to seven layers. Researchers have now developed an OLED that consists of a single layer powered by two electrodes. This simplifies the production of such OLEDs and opens the way to printable screens.

With their first prototype, the scientists of Mainz were able to show that they could generate a luminosity of 10,000 candelas / square meter with a voltage of only 2.9 volts, about 100 times the brightness of modern screens. Achieving such brightness at this low voltage is a record for current OLEDs. The researchers were also able to measure an external efficiency of 19%, which means that 19% of the electrical energy supplied is converted into a light that comes out in the direction of the observer. In addition, with this value, the OLED prototype can compete with current OLEDs composed of five or more layers.

In continuous operation, researchers have been able to measure a so-called LT50 lifetime of nearly 2000 hours with a brightness equivalent to ten times that of modern screens. During this period, the initial brightness dropped to 50% of its value.

"In the future, we hope to further improve the concept and extend its life, which means that the concept could be used for industrial purposes," said Wetzelaer. Scientists hope that their new concept monolayer developed, namely. the reduced complexity of OLEDs will contribute to the identification and improvement of the processes responsible for the reduction of the service life.

Scientists use a luminescent layer based on "thermally activated delayed fluorescence" (TADF). This physical principle has been known for several decades, but it became the focus of OLED research about 10 years ago, when efficient conversion of electrical energy into light was demonstrated in Japan. Since then, researchers have been working on TADF-based OLED production because they do not require expensive molecular complexes containing rare earth metals that are used in current OLEDs.

The researchers have now published their findings in the famous journal Photonic Nature.

New technique can lighten screens and extend the life of smartphone batteries

More information:
Naresh B. Kotadiya et al, efficient and stable single-layer organic electroluminescent diodes based on thermally activated delayed fluorescence, Photonic Nature (2019). DOI: 10.1038 / s41566-019-0488-1

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On the path of printable organic light-emitting diodes (July 10, 2019)
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