Light bulbs and fluorescent tubes are far away from the optimal efficiency, while OLED can offer new perspectives for novel large area light sources for display and lighting applications. Such displays are increasingly applied to mobile telephones, digital cameras, or pocket computers. In future these small light miracles will play an important role for TV screens and for lighting. Now, the Institute für Angewandte Photophysik (IAPP) of the Technical University Dresden has achieved new record values for the energy efficiency of organic light-emitting devices.

The LED, which are developed by Rico Meerheim and the OLED group of the IAPP, achieve an energy yield of 26, 22, and 3.1 percent at a brightness of a computer screen for the three base colors red, green, and blue, respectively, corresponding to power efficiencies of 81, 101, and 4 lumens per watt. The values for red OLEDs exceed all existing efficiencies by far. Besides displays, these three base colors also constitute the basis for white OLEDs.

Since white OLEDs are needed for lighting applications, their efficiency enhancement is under intensive investigation. In comparison, conventional light bulbs only reach an energy yield of 5 percent. The efficiency of LED is of high relevance, because by this the energy consumption can be strongly reduced while keeping the brightness constant. Furthermore particularly red OLEDs show stable light emission over several decades, which is crucial for product applications. According to Prof. Dr. Karl Leo of IAPP, for these highly efficient OLEDs exists many novel applications. This applies especially for red diodes, which can be used for indicator elements.

For the LED developed in Dresden, the scientists have stacked layer-kind organic dyes in a certain sequence. Furthermore, the electronic properties of the layer structure were optimized carefully. By a new optical concept, the scientists achieved a change of the light paths through the organic layers and the glass substrate, resulting in a higher ratio of light outcoupled from the device. Thereby, the same brightness will be achieved by lower current, i.e. the energy yield increases. Dipl. Phys. Rico Meerheim form IAPP, said: “The reduced energy consumption of OLEDs due to their high energy yield will contribute to a way out of the world energy crisis.”

The results achieved at the Technical University Dresden are obtained in a close cooperation with the spin-off company Novaled. Dr. Jan Blochwitz-Nimoth form Novaled AG comments: “For Novaled AG, global market leader in the field of high efficient OLED, this development is another demonstration that further efficiency enhancements of OLEDs are achievable by an appropriate optimization of the optical characteristics. The results of our long standing research partner IAPP show one times more the potential of the Novaled PIN technology that is here nice shown for the example of the microcavity optimization.”