High-Performance Deep-Blue OLEDs Harnessing Triplet-Triplet Annihilation Under Low Dopant Concentration

Organic blue emitters capable of proceeding triplet-triplet annihilation (TTA) are of great importance for high-efficiency blue organic light-emitting diodes (OLEDs). Herein, two deep-blue emitters PAPE and PAPF with two diphenylanthracene (DPA) moieties linked by fluorene and ether, respectively, together with a single DPA model emitter PAPES are synthesized and characterized. Theoretical calculations indicate that the TTA mechanism of these materials is energetically favorable, which is evidenced by platinum octaethylporphyrin-sensitized TTA-upconversion (UC) study. The OLED devices employing o-DiCbzBz host doped with a low concentration of (1%) PAPE and (3%) PAPF furnish superior maximum external quantum efficiency (EQE(max)) up to 7.3% and 7.2% and realize deep-blue emissions with Commission International de L'Eclairge (CIE) coordinates of (0.15, 0.05) and (0.15, 0.04), respectively, that outperform the model device doped with (1%) PAPES with EQE(max) 4.12%. The delayed emission lifetimes from TTA of PAPE- and PAPF-doped devices observed by the time-resolved electroluminescence (EL) analyses are rather short. Fast TTA is observed with magneto-electroluminescence, supporting the possibility of intramolecular TTA operation in the devices. This work manifests the potential of multichromophoric strategy to design fluorescent emitters that is able to boost the efficiency of deep-blue OLEDs even with a low doping concentration.