Highly efficient deep blue phosphorescent organic light‐emitting diodes (PHOLEDs) with external quantum efficiency above 20% are developed using a bipolar‐type high‐triplet‐energy host material and a high‐triplet‐energy exciton blocking material. Maximum quantum efficiency of 25.1% and low roll‐off (still 23.1% at 1000 cd m−2) are achieved in these deep blue PHOLEDs.
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