Concentration-insensitive and low-driving-voltage OLEDs with high efficiency and little efficiency roll-off using a bipolar phosphorescent emitter

• Highly efficient PHOLEDs based on a bipolar iridium emitter have been demonstrated.
• PHOLEDs show gratifying concentration-insensitive and low-driving-voltage feature.
• EQE values maintain at more than 20% in very wide luminance range of 1–15,000 cd m−2.

A series of simplified trilayer phosphorescent organic light-emitting diodes (PHOLEDs) with high efficiency and little efficiency roll-off based on a bipolar iridium emitter Iridium(III) bis(2-phenylpyridinato)-N,N′-diisopropyl-diisopropyl-guanidinate (ppy)2Ir(dipig) has been demonstrated. They are dominated by the efficient direct-exciton-formation mechanism and show gratifying concentration-insensitive and low-driving-voltage features. In particular, very high and stable electroluminescence (EL) efficiencies (maximum power efficiency and external quantum efficiency >98 lm W−1 and 25% respectively, and external quantum efficiency >20% over a wide luminance range of 1–15,000 cd m−2) are achieved in the PHOLEDs based on emitting layers (EMLs) consisting of (ppy)2Ir(dipig) codeposited with common host CBP in an easily controlled doping concentration range (15–30 wt%). The EL performance of the PHOLEDs is comparable to the highest PHOLEDs reported in scientific literature.

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