An efficient, stable OLED based on a single layer of a neat, thermally activated, delayed fluorescence emitter has been demonstrated by a research group at the Max Planck Institute for Polymer Research (MPI-P). The first prototype of the single-layer OLED is comparable in luminosity and efficiency to commercially available OLEDs. The new OLED design consists of a layer that is supplied with electricity via two electrodes. The light-emitting layer is based on thermally activated delayed fluorescence (TADF). TADF-based OLEDs do not require expensive molecular complexes containing rare-earth metals like those being used in current OLEDs, the researchers said. The first prototype of the OLED developed in Mainz, Germany, illuminates the MPI-P logo. Courtesy of MPI-P/License CC-by-SA. With their first prototype, the MPI-P scientists generated a low operating voltage of 2.9 V at a luminance of 10,000 cd m−2. According to the team, such high luminosity at such a low voltage is a record for current OLEDs. Balanced electron and hole transport resulted in a maximum external quantum efficiency of 19% at 500 cd m−2 and a broadened emission zone. In continuous operation, the stable, single-layer OLED prototype allowed a lifetime to 50% of the initial luminance of 1,880 h for an initial luminance of 1,000 cd m−2 — a brightness equivalent to 10 times that of modern displays, the researchers said. The single-layer concept simplifies the production process without lowering performance and efficiency, and paves the way for printable OLED displays. “For the future, we hope to be able to improve the concept even further and thus achieve even longer lifetimes,” group leader Gert-Jan Wetzelaer said. “This means that the concept could be used for industrial purposes.” Compared to conventional LEDs, the luminosity and lifetime of OLEDs are lower. The MPI-P scientists hope that their newly developed single-layer concept, by reducing OLED complexity, can be used to help improve the processes that cause reduced luminance in OLEDs over time. The research was published in Nature Photonics (https://doi.org/10.1038/s41566-019-0488-1).
