Hyo Suk Son

External quantum efficiency above 20% in deep blue phosphorescent organic light-emitting diodes.

The development of high-effi ciency blue-light-emitting phosphorescent organic light-emitting diodes (PHOLEDs) is important in order to reduce the power consumption of organic light-emitting diodes (OLEDs) in display and lighting applications. [ 1–10 ] Iridium(III) bis(4,6-(difl uorophenyl)-pyridinatoN , C ′ ) picolinate (FIrpic) has typically been used as the dopant material for blue PHOLEDs, with a theoretical maximum quantum effi ciency of 20% already reported in sky blue PHOLEDs using various host and exciton blocking materials. [ 11–14 ] Although 20% external quantum effi ciency was achieved in sky blue PHOLEDs, it could not be achieved in deep blue PHOLEDs owing to the requirement of high triplet energy of the host and deep blue dopant material. Our group has reported a 19.2% maximum external quantum effi ciency in deep blue PHOLEDs, but the effi ciency could not be further improved. [ 8 ] Moreover, the quantum effi ciency dropped sharply at high luminance, and therefore high quantum effi ciency could not be achieved above 100 cd m − 2 . [ 2 ] In particular, the quantum effi ciencies at 1000 cd m − 2

Correlation of the substitution position of diphenylphosphine oxide on phenylcarbazole and device performances of blue phosphorescent organic light-emitting diodes

Two diphenylphosphine oxide modified phenylcarbazole host materials with substituents at 2,7 (PPO27) and 3,6 (PPO36) positions were synthesized and their device performances were correlated with the chemical structure of the host materials. Low driving voltage was obtained in the PPO27host with two diphenylphosphine oxides at 2,7 positions due to reduced band gap. The PPO27 showed better performances in sky blue phosphorescent organic light-emitting diodes, while the PPO36 showed better performances in deep blue phosphorescent organic light-emitting diodes. A high quantum efficiency of 23.9% and power efficiency of 37.5 lm W−1 were achieved in the blue device with PPO27host.

Ethylcarbazole Based Phosphine Oxide Derivatives as Hosts for Blue Phosphorescent Organic Light-Emitting Diodes

Blue phosphorescent organic light-emitting diodes were developed using host materials with 9-ethylcarbazole and phosphine oxide units and they could be used in blue phosphorescent organic light-emitting diodes. Efficient energy transfer from the ethylcarbazole based hosts to the blue phosphorescent dopant material was observed due to the high triplet energy of the host material.