Efficient Solution-Processed Hyperfluorescent Oleds With Spectrally Narrow Emission At 840 Nm

To reduce cost and improve environmental sustainability, there continues to be an important need for the development of efficient organic light-emitting diodes (OLEDs) that do not rely on heavy metal-containing compounds. In particular, the efficiency of fluorescent near-infrared (NIR) OLEDs continues to lag well-behind that of their platinum-containing counterparts. Low efficiencies in this spectral range mainly arise from the low quantum yields of fluorescent NIR emitters due to the energy gap law and inefficient harvesting of triplet excitons. In this paper, a thermally activated delayed fluorescent (TADF) material is used as the assistant dopant to demonstrate pure NIR-emitting fluorescent OLEDs with an external quantum efficiency of up to 3.8%, with an electroluminescence maximum at 840 nm and a spectral full-width at half-maximum of < 40 nm. The efficiency is more than three times higher than that of the best previously reported fluorescent OLEDs in this spectral range and approaches that achievable with the best platinum-containing phosphorescent emitters.