Reseachers from the Universities of Bonn, Regensburg, Utah and the MIT developed a new method to make triplets radiate directly in OLEDs rather than harvesting the triplets by reverse intersystem crossing to generate delayed fluorescence. Basically this means they enabled phosphorescence OLEDs without any heavy atoms at room temperature.

The researchers created new emitter molecules that can store electrical energy for significantly longer than is conventionally assumed. This means that these molecules can exploit the spontaneous jumps in spin orientation in order to generate light - so the energy that is lost as heat in regular fluorescent OLEDs is released as light in those molecules.

In past years we heard of another method to reach high efficiency in fluorescent OLEDs by using the Singlet-Harvesting Principle - what is referred to as Thermally Activated Delayed Fluorescence (TADF, also called delayed fluorescent). TADF OLED emitters are being commercialized by Cynora (based on copper) and is also being independently researched at Kyushu University.

Professor John M. Lupton from the University of Regensburg explains that their new technology is very different from TADF - "we've actually developed a trick to make the triplets radiate directly (phosphorescence) rather than harvesting the triplets by reverse intersystem crossing to generate delayed fluorescence. TADF is temperature sensitive (you need heat to get from the triplet to the singlet), whereas phosphorescence is not".



Professor Lupton further explains that in their molecules, the spin information of the electron-hole pair is maintained (whereas TADF is based on spin mixing). This could lead to more exotic OLED applications, for example as very sensitive magnetic field sensors (see here for example). These new materials could allow you to read out the spin of the electron optically (by luminescence).

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