OLED with Only One Single Layer

The first prototype of the single layer OLED developed in Mainz, Germany, illuminates the logo of the research institute. (Source: MPI-P)

Scientists at the Max Planck Institute for Polymer Research led by group leader Gert-Jan Wetzelaer have now developed a new OLED concept. Nowadays, OLEDs consist of various wafer-thin layers. Some layers are used to transport 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. The researchers have now developed an OLED which consists only of one single layer that is supplied with elec­tricity via two electrodes. This simplifies the pro­duction of such OLEDs and paves the way for printable displays.

With their first proto­type, the Mainz scientists were able to show that they can generate a brightness of the emitted light of 10,000 candela per square meter with a voltage of only 2.9 volts. This corresponds to about one hundred times the luminosity of modern screens. Achieving such high lumi­nosity at this low voltage is a record for current OLEDs. The researchers were also able to measure an external effi­ciency of 19%. Also with this value, the OLED proto­type can compete with current OLEDs consisting of five or even more layers.

In continuous operation, the researchers were able to measure a LT50 lifetime of almost two thousand hours at a brightness equivalent to ten times that of modern displays. Within this time, the initial lumi­nosity has dropped to fifty percent of its value. “For the future, we hope to be able to improve the concept even further and thus achieve even longer lifetimes. This means that the concept could be used for indus­trial purposes,” says Wetzelaer. The scientists hope that their newly developed single-layer concept – i.e. the reduced com­plexity of OLEDs – will contribute to the identi­fication and improvement of the processes responsible for the reduction in luminance over time.

The scientists are using a light-emitting layer based on “Ther­mally Activated Delayed Fluores­cence” (TADF). This physical principle has been known for several decades, but became the focus of OLED research about ten years ago, when an effi­cient conversion of elec­trical energy into light was demon­strated in Japan. Since then, researchers have been working to produce TADF-based OLEDs, as these do not require expensive molecular complexes containing rare-earth metals that are being used in current OLEDs. (Source: MPI-P)

Reference: N. B. Kotadiya et al.: Efficient and stable single-layer organic light-emitting diodes based on thermally activated delayed fluorescence, Nat. Phot., online 8 July 2019; DOI: 10.1038/s41566-019-0488-1

Link: Dept. of Molecular Electronics, Max Planck Institute for Polymer Research, Mainz, Germany

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