BASF and OSRAM Opto Semiconductors have developed a highly efficient white organic light-emitting diode (OLED). For the first time, an OLED not only is able to achieve a light yield of more than 60 lumens per watt (lm/W), but also, at the same time, meets the international Energy Star SSL Standard with regard to color requirements. Lighting efficiency describes the ratio of luminous flux given off by a lamp to the amount of power consumed; the greater the yield, the less energy is lost. Although this efficiency benchmark had previously been achieved, until now the color values of OLEDs have not been within the acceptable band for color coordinates around the Planck curve, as defined by the ENERGY STAR SSL Standard. The color values of the new OLED are within this band – its light retains the white color at different levels of intensity.
By developing a white OLED with a high light yield, the two companies have completed a major step on the way toward commercial OLED lighting. In the development laboratories of Siemens Corporate Technology (OSRAM is part of the Industry sector of Siemens), highly efficient semiconductor materials from BASF Research were combined with standard materials – and thereby new standards set with regard to color coordinates and efficiency. BASF and OSRAM are conducting this research together within the framework of the “OLEDs for Applications on the Lighting Market” (OPAL) project. The OPAL project is being sponsored as part of the OLED Initiative of the German Federal Ministry for Education and Research (BMBF).
The new OLEDs contain phosphorescent metal complexes as emitter materials and customized complementary materials, which ensure optimum constancy of the color temperatures. That means that, owing to the use of new materials, the diodes are very color-stable even when there are variations in luminous intensity. The challenge now is to optimize the life of these OLED tiles, especially by stabilizing the blue emitters.