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 over 60 lumens per watt (lm/W), but also, at the same time, meets the international Energy Star SSL Standard with regard to color requirements.
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.
Printed Electronics World reported lighting efficiency greater that this by Universal Display Corporation who earlier this year demonstrated a record-breaking white OLED with a power efficacy of 102 lumens per watt (lm/W) at 1000 cd/m2 but they used their proprietary, high-efficiency phosphorescent OLED technology.
What makes this efficiency different to others?
In understanding the differences between the claims, Dr. Heuser, the OPAL Coordinator and Director OLED Lighting Technology at OSRAM Opto Semiconductors, explained the following to Printed Electronics World:
"Our devices are made with a thin film light extraction film on top of the glass. If you would use a macroscopic extraction geometry, you could increase efficiency significantly. On the other side, the power efficiency for a certain color is very important. If you would move the color coordinates (CIE coordinates) from the SSL requirements towards higher y coordinates (means towards green from the white point) you would directly increase the power efficiency, since the eye sensitivity of the human eye is higher in green. Therefore the same quantum efficiency is leading to different power efficiencies for different CIE coordinates. For future applications the color point within the SSL Star requirement is essential for white."
White OLEDs are readily color tunable and can go from cool to warm whites.
How is lighting efficiency defined?
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.
But according to OSRAM, up 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.
OSRAM and BASF believe that they have moved closer towards commercial OLED lighting with the devlopment of a white OLED with a high light yield but now need to optimize the life of these OLED tiles, especially by stabilizing the blue emitters.
"The challenge now lies with the process engineers to apply these high efficiencies economically to large active areas," says Dr. Heuser.
The lighting solution of the future
OLEDs consume less energy and do not become hot unlike conventional filament bulbs. The researcher's claim that their new OLEDs are five times as efficient as filament bulbs and up to 50% more efficient compared with standard low-energy lamps thus offering reduced electricity costs to consumers . New and exciting opportunites will be available in terms of design and performance such as flexible lighting for architectural and general purposes.
BASF reached an important milestone in OLED research a few years ago. White light from OLEDs can best be obtained by combining red, green and blue light. For a long time there was no efficient source for deep-blue light.
BASF and OSRAM are conducting 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).
For more attend Printed Electronics Europe 2009.
References: Osram; Universal Display Corporation