Efficacy of 45 lm/W Achieved in White OLED

Photo of four light sources:  a large white square containing grid lines, a smaller bright white square, an incandescent light bulb, and a tube fluorescent light bulb

UDC white OLED prototypes are pictured next to fluorescent and incandescent lamps.

A line chart with Total Power Efficacy (lm/W) on the vertical axis and Luminance (cd/m2) on the horizontal axis.  A line starts on the left at about 53 lm/W and gradually goes down as luminance increases.  The line goes down to 45 lm/W at 1000 cd/m2 and keeps descending until it reaches about 33 lm/W at 5,000 cd/m2.
A line chart with Intensity (Watts/sr.m2.nm) on the vertical axis and Wavelength (nm) on the horizontal axis.  The bottom horizontal line is slightly wavy and represents (0.39, 0.44) at 1,000 nits; the line above it is more wavy and represents (0.38, 0.44) at 3,000 nits; the top line is the most wavy and represents (0.38, 0.44) at 5,000 nits.

Figures 1 and 2 detail efficacy and electroluminescence characteristics for the 45 lm/W OLED device.

Universal Display Corporation (UDC) successfully demonstrated an all phosphorescent white organic light emitting diode (WOLED™) with a power efficacy of 45 lm/W at 1,000 cd/m2. This high-efficacy device was enabled by lowering the device operating voltage, increasing the outcoupling efficiency to ~40% from ~20%, and by incorporating highly efficient phosphorescent emitters that are capable of converting nearly all current passing through a WOLED into light.

Low voltage operation is obtained by incorporating highly conductive transport layers and by designing devices to improve charge injection and recombination in the emissive layer. The outcoupling efficiency was enhanced by using OLED luminaires that significantly reduce the absorption losses incurred when light waveguides in the substrate. Near 100% internal quantum efficiency is realized by using phosphorescent OLEDs (PHOLEDs) whereas only 25% internal quantum efficiency is typically obtained from fluorescent devices. In PHOLEDs, the singlet excited state (S1) excitons may be converted into the triplet excited state (T1) through inter-system crossing via the presence of a heavy metal atom. In these devices, the triplet states can emit radiatively (T1 to S0), enabling record high conversion efficiencies.

Warm white emission from the device has a color rendering index of 78 at (0.38, 0.44), and this color was chosen because it more closely resembles the color of incandescent lamps, which WOLEDs are targeted to replace in the illumination market.

The UDC team will continue to work on further improvements. In 2008, UDC expects to deliver a high-power prototype lighting panel with a power efficacy of  40 lm/W at 100 lm. The high lumen output will be achieved by using a large area (~6-in-sq.) panel, and the OLED architecture will be based on the device described above. The team is also targeting a 100 lm/W white OLED by 2010, which is well in line with the DOE multi-year projection for white OLED light sources.