Solution-Processible Red Iridium Dendrimers based on Oligocarbazole Host Dendrons: Synthesis, Properties, and their Applications in Organic Light-Emitting Diodes

Graphical Abstract

Multifunctional red iridium dendrimers suitable to low-cost solution processing technologies have been synthesized and used for electrophosphorescent devices by associating oligocarbazole host as dendrons with red emissive Ir complex dopant as the core. With the third-generation dendrimer red-G3, the peak external quantum efficiencies of 6.3% for non-doped devices and 11.9% for doped devices have been demonstrated, which are well comparable with those of vacuum-deposited small molecular phosphors.

Abstract

A series of novel red-emitting iridium dendrimers functionalized with oligocarbazole host dendrons up to the third generation (red-G3) have been synthesized by a convergent method, and their photophysical, electrochemical, and electroluminescent properties have been investigated. In addition to controlling the intermolecular interactions, oligocarbazole-based dendrons could also participate in the electrochemical and charge-transporting process. As a result, highly efficient electrophosphorescent devices can be fabricated by spin-coating from chlorobenzene solution in different device configurations. The maximum external quantum efficiency (EQE) based on the non-doped device configuration increases monotonically with increasing dendron generation. An EQE as high as 6.3% was obtained as for the third generation dendrimer red-G3, which is about 30 times higher than that of the prototype red-G0. Further optimization of the device configuration gave an EQE of 11.8% (13.0 cd A⁻¹, 7.2 lm W⁻¹) at 100 cd m⁻² with CIE coordinates of (0.65, 0.35). The state-of-the-art performance indicated the potential of these oligocarbazole-based red iridium dendrimers as solution processible emissive materials for organic light-emitting diode applications.