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.