New OLED achieves high efficiency without heavy metals

Ars Technica : Organic LEDs are thin, flexible materials that create light from electrically stimulated fluorescence. Electricity passing through an OLED excites both electrons and holes (their positive counterparts). When the electrons and holes meet, they form bound states called excitons that can be either singlet or triplet. The singlet excitons, which only form 25% of the time, release their bound energy as light; the triplets release their energy as heat. Adding heavy metal atoms to OLEDs yields almost 100% light emission, but heavy metals can be expensive. Hiroki Uoyama of Kyushu University in Japan and his colleagues have created a new OLED that maintains nearly the same level of light emission without the use of heavy metals. By carefully designing the OLED molecule, they were able to reduce the energy difference between singlet and triplet excitons so that the triplets converted into singlets and then released their energy as light. The engineered molecule still needs to be able to match the full abilities of heavy metal OLEDs before it will be useful in commercial devices.