Star-shaped dendritic hosts based on carbazole moieties for highly efficient blue phosphorescent OLEDs

Abstract

An efficient carbazole-based dendritic host material Cz-TCB for solution processed blue phosphorescent organic light-emitting devices (PhOLEDs) was designed and synthesized. The nonplanar star-shaped configuration of Cz-TCB limited the effective extension of their π-conjugation, leading to the same triplet energy of 2.86 eV. No noticeable signals of Cz-TCB related to glass transition is observed in the DSC curves. Atomic force microscopy (AFM) measurements indicate the excellent thermal and morphological stability of the dendrimer. The performance of the novel host material based devices is far superior to those of the corresponding 1,3,5-tri(N-carbazolyl)benzene (TCB) based devices, which is outstanding for a solution-processed blue PhOLED. The best performance of iridium(III) bis(4,6-(di-fluorophenyl)-pyridinato-N,C′ (FIrpic) based devices show a turn-on voltage of 4.6 V, a maximum external quantum efficiency of 13.0%, and a maximum luminance efficiency of 25.7 cd A⁻¹. Moreover, the best performance of iridium(III) tris(3,5-difluoro-4-cyanophenyl)pyridinato-N,C′ (FCNIrpic) based deep-blue-emitting devices exhibits a turn-on voltage of 5.7 V, a maximum efficiency of 10.9 cd A⁻¹, and a maximum external quantum efficiency 6.4%. Our results demonstrate a promising approach to well-designed dendritic host materials for solution-processed blue PhOLEDs.