Sang Eok Jang

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

Fabrication and Efficiency Improvement of Soluble Blue Phosphorescent Organic Light‐Emitting Diodes Using a Multilayer Structure Based on an Alcohol‐Soluble Blue Phosphorescent Emitting Layer

The development of soluble phosphorescent organic lightemitting diodes (PHOLEDs) is important because the low effi ciency of soluble fl uorescent organic light-emitting diodes (OLEDs) can be improved by using soluble PHOLEDs instead. [ 1–3 ] In particular, the effi ciency of soluble blue OLEDs is quite low compared to red and green OLEDs, and the development of high-effi ciency soluble blue PHOLEDs is strongly required. A great deal of research has been focused on enhancing the effi ciency of soluble blue PHOLEDs using various device architectures and emitting materials. [ 4–14 ] The most effi cient method of improving the quantum effi ciency of soluble blue PHOLEDs was to use a mixed host emitting layer with hole and electron type host materials. Typically, poly(N-vinylcarbazole) (PVK) has been used as the hole transport type host material and 1,3-bis[(4-tertbutylphenyl)-1,3,4-oxadiazolyl]phenylene has been applied as the electron transport type host material. [ 6–14 ] A high effi ciency of 22 cd/A can be achieved in a solution-processed blue PHOLED because of the charge balance in the emitting layer. [ 9 ] Fluorinated PVK is better than common PVK, and 27 cd/A is the best effi ciency that has been reported. [ 11 ] PVK can also be blended with a phosphine oxide based electron transport type host material in order to enhance the effi ciency compared to the PVK only device. [ 15 ] Soluble small-molecule host-based blue PHOLEDs have also been developed with a current effi ciency of 12.7 cd/A. However, the effi ciency of solution-processed blue PHOLEDs cannot be further improved because of the limitations of the multilayer structure fabrication even though a crosslinkable hole transport material has been applied in these solutionprocessed PHOLEDs. [ 6 ] A high triplet energy hole transport layer is critical to the quantum effi ciency of blue PHOLEDs, [ 17 ]

High Power Efficiency in Blue Phosphorescent Organic Light-Emitting Diodes Using a Spirobifluorene Phosphine Oxide Compound

High power efficiency blue phosphorescent organic light-emitting diodes (PHOLEDs) were fabricated using a mixed host of 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) and 2,7-bis(diphenylphosphoryl)-9,9’-spirobi[fluorene] (SPPO13) in the emitting layer. A maximum power efficiency of 33.7 lm/W and a high power efficiency of 28.4 lm/W at 1,000 cd/m2 were achieved in the blue PHOLED with the mixed host emitting layer of TAPC and SPPO13. The efficiency roll-off of the device was also reduced by using the mixed host emitting layer.