Efficient green phosphorescent organic light-emitting diodes enabled with new and thermally stable carbazole/pyridine derivatives as hosts

Two host materials H1 and H2 by introducing dibenzothiophene and dibezofuran moieties into the carbazole and pyridine derivative, respectively, are reported. Their structural and physical properties were fully characterized. The thermal analysis demonstrated that both H1 and H2 are thermally stable. The triplet energy levels of H1 and H2 were determined to be 2.66 and 2.51 eV, respectively. Green phosphorescent OLEDs with H1 and H2 acting as host materials were fabricated to investigate their performances in PHOLEDs . Green PHOLED based on H1 shows the best performance with the maximum power efficiency of 50.4 lm/W and the lowest driving voltage of 2.5 eV. The characteristic measurements of OLED devices reveal that both H1 and H2 are promising host materials for practical application. By comparing with the commercial host material of 4,4′-bis(carbazol-9-yl)biphenyl (CBP), the power efficiency of green PHOLED was enhanced by 31.6%.