Improved Lifetime and Efficiency of Blue Phosphorescent OLEDs Based on Bicarbazole-Triazine Hybrid Type Mixed Host Materials
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초록
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We developed a series of four p-type blue host molecules and an n-type host molecule to achieve blue phosphorescent OLEDs (PhOLEDs) with a long operational lifetime and high efficiency. With different substitutional positions of carbazole and triphenyl-silyl groups, we effectively control the photophysical- and charge transport behaviors and binding dissociation energies of the molecules. Using one of four p-type hosts and an n-type host, we properly controlled the charge carrier balance and reduced the trapped polarons in the emitting layer under electrical operation. As a result, we realized high-performance blue PhOLEDs, showing a maximum external quantum efficiency (EQE) of 20.1%, a low-efficiency roll-off (13.3% of EQE at 10,000 cd m2 ), and an operational lifetime of 51 hours (T50 at 500 cd m2 ).