Abstract
The commercialization of high efficiency OLEDs is set to revolutionize lighting and display technologies in the near future. Whilst efficient red and green emitters based upon phosphorescent organometallic emissive materials are available1, the development of deep blue emitters has remained a challenge. For most fluorescent organic light emitting diodes (OLEDs), the internal quantum efficiency (IQE) is capped at 25% owing to the inability of most organic materials to emit light from the statistical 75% of electrically generated triplet excitons. By exploiting spin orbit coupling of a phosphorescent heavy metal complex it is possible to ‘harvest’ triplet excitons inaccessible to singlet fluorescent emitters. An alternative way to overcome this limitation is to use organic light emitting materials that have a narrow S1 – T1 energy gap. In such a material, thermal population of the triplet excitons into the singlet state at ambient temperature is possible thus allowing an organic material to harvest both singlet and triplet excitons via a fluorescent emission pathway. This phenomena of enhanced fluorescence is known as thermally activated delayed fluorescence (TADF) and allows a fluorescent OLED containing TADF emitting materials to achieve a theoretical internal quantum efficiency of 100%.
© 2014 Optical Society of America
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