Issue Date: May 3, 2004
POLYMER OLED EFFICIENCY BOOST
Two developments that significantly increase the efficiency of polymer organic light-emitting diodes could lead to low-cost, large-scale manufacturing of polymer OLED displays, according to scientists at Philips Research in Eindhoven, the Netherlands.
In the first development, the group showed that a novel anode layer reduces the waste of energy that arises from imbalances between the hole (positive charge) and electron partial currents in polymer OLED devices. The new layer is a "hydrocarbon-based polymer with heteroatoms," according to Philips. It introduces a barrier to hole injection to reduce the number of excess holes. As a result, the quantum efficiency of the device increases to around 12%, compared with 2 to 4% for standard devices.
The second development improves polymer OLED efficiency by dispersing a phosphorescent guest material into a light-emitting polymer host. In collaboration with TNO Industrial Technology, Eindhoven, the Philips Research team showed that a polymer of a carbazole-oxadiazole derivative can be employed to host a high-energy phosphorescent iridium complex as a guest.
"These breakthrough developments point the way for the future in which we fully expect to see increases approaching 10-fold in polymer OLED efficiency without any compromise of the technology's inherent simplicity and easy manufacturability," says Philips Research principal scientist Eric A. Meulenkamp. "Along with other developments in the pipeline, this could lead to polymer OLED technology overtaking liquid-crystal display technology to become one of the major display technologies of the future."
Meulenkamp presented the work on April 28 at the International Society for Optical Engineering's Photonics Europe conference in Strasbourg, France. Some results were just published [J. Am. Chem. Soc., published online April 23, http://dx.doi.org/10.1021/ja049883a].
Philips anticipates that the work will open the way to lower power consumption and will further strengthen the inherent advantages of polymer OLEDs such as high brightness and contrast and wide viewing angle. It should also enable the use of polymer OLEDs in solid-state light applications.
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