Abstract
Phosphorescent organic light-emitting diodes (PhOLEDs) have manifested enormous potential for display and lighting applications because of their high internal and external quantum efficiencies, nevertheless, severe efficiency roll-off at high luminance remains a major bottleneck in their large-scale commercialization. Herein, two new bipolar host compounds, DCbz-Ph-Bz and DDPA-Ph-Bz, based on carbazole/diphenylamine as the donor and benzimidazole as the acceptor, are successfully obtained. By employing these materials as hosts, extremely low efficiency roll-off PhOLEDs without sacrificing the efficiency are realized. Especially, green PhOLED based on DDPA-Ph-Bz as the host and GD001 as the dopant demonstrated a low turn-on voltage of 2.6 V, a peak current efficiency (CE) of 62.2 cd/A and a maximum luminance of 39,370 cd/m2. Importantly, our green device exhibited a very low efficiency roll-off as the peak external quantum efficiency (EQE) of 18.3% at 1000 cd/m2 was still retained at 17.6% even at a high luminance of 10,000 cd/m2. Likewise, red PhOLED with DCbz-Ph-Bz as the host and RD001 as the dopant displayed a high maximum EQE of 20.1% and a CE of 24.5 cd/A. High efficiency with low efficiency roll-off in our devices reveals the potential of bipolar molecules as excellent hosts to achieve high-performance PhOLEDs.
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