A Macrospirocyclic Carbazole-Fluorene Oligomer As A Solution-Processable Matrix Host Material For Blue Phosphorescent Organic Light-Emitting Diodes With Low Turn-On Voltage And Efficiency Roll-Off
JOURNAL OF PHYSICAL CHEMISTRY C(2017)
摘要
The use of mixed hosts has been demonstrated to be an effective way to improve the efficiency of phosphorescent organic light emitting diodes (PhOLEDs). In this study, a macrospirocyclic oligomer (Cz-F)(4) based on carbazole and fluorene is synthesized as a solution-processable matrix host material for blue PhOLEDs. The oligomer exhibits a high triplet level, good film-forming ability, solution processability, and doping compatibility. As a result, a blue solution-processed PhOLED based on a (Cz-F)(4)/TAPC [1,1-bis((di-4-tolylamino) phenyl) cyclohexane] mixed host achieves a maximum current efficiency of 18.8 cd/A with a turn-on voltage of 3.3 V. When a ternary mixed-host system composed of (Cz-F)(4), TAPC, and OXD-7 [1,3-bis(5-(4-(tert-butyl)phenyl)-1,3,4-oxadiazol-2-yl)benzene] is employed, the device exhibits a low turn-on voltage of 2.8 V, and the driving voltages are only 3.8-4.6 V at the practical luminance of 100-1000 cd/m(2). Even at 5000 and 10 000 cd/m(2), the driving voltages are only 5.7 and 6.6 V, respectively. The current efficiency roll-off is only 12% from 100 to 5000 cd/m(2). This study demonstrates that monodisperse oligomers can serve a matrix host for highly efficient blue solution-processed PhOLEDs with low turn-on voltage) low driving voltage, and suppressed efficiency roll-off.
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