The path toward creating an electrically pumped organic laser is hindered by the fact that metallic contacts quickly absorb light in organic light-emitting diodes (OLEDs) and other organic lasing structures. Because OLEDs with typical organic layer thickness of 80 to 100 nm generate light very close to the metallic cathode (within 50 nm), severe absorption losses occur when the OLED is used as a waveguide. And while thicker OLEDs would eliminate this problem, their low carrier mobility gives rise to high electrical resistance and OLED efficiency is compromised. But by using an organic LED with a remote metallic contact, researchers at IMEC (Leuven, Belgium) have created an electrically pumped, vertical-transmission light-emitting organic device that reduces optical absorption and at the same time allows for high current densities; both interesting features with respect to the realization of an organic electrically pumped laser.
Unlike conventional OLEDs in which charge transport occurs perpendicularly to the organic layers, electrons are transported in the plane of the layers by field-effect mobility. In this way the light-emission zone can be located one to several microns away from the metallic cathode. The researchers were able to successfully demonstrate 636 nm vertical emission from the 1 mm wide organic device in a 2-µm-wide emission zone. Contact Sarah Schols at [email protected].