Abstract
AbstractRecently, bipolar host materials are the most promising candidates for achieving high performance phosphorescent organic light‐emitting diodes (PHOLEDs) in order to maximize recombination efficiency. However, the development of host material with high triplet energy (E T) is still a great challenge to date to overcome the limitations associated with the present PHOLEDs. Herein, a highly efficient donor‐π‐acceptor (D‐π‐A) type bipolar host (4′‐(9H‐carbazol‐9‐yl)‐2,2′‐dimethyl‐[1,1′‐biphenyl]‐4‐yl)diphenylphosphine oxide (m‐CBPPO) comprising of carbazole, 2,2′‐dimethylbiphenyl and diphenylphosphoryl as D‐π‐A unit, respectively, is developed. Interestingly, a high E T of 3.02 eV is observed for m‐CBPPO due to highly twisted conformation. Furthermore, the new host material is incorporated in PHOLEDs as emissive layer with a new carbene type Ir(cb)3 material as a deep‐blue emitter. The optimized devices show an excellent external quantum efficiency (EQE) of 24.8% with a notable Commission internationale de l'éclairage (x, y) ≤ 0.15, (0.136, 0.138) and high electroluminescence performance with extremely low efficiency roll‐off. Overall, the above EQE is the highest reported for deep‐blue PHOLEDs with very low efficiency roll‐off and also indicate the importance of appropriate host for the development of high performance deep‐blue PHOLEDs.
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