Ultrahigh Energy Gap Hosts in Deep Blue Organic Electrophosphorescent Devices

The authors discuss the material design, and present device data for OLEDs employing UGHs. In addition to showing that UGH materials can be used to fabricate efficient blue OLEDs, we demonstrate that very high device efficiencies can be achieved in structures where the dopant transports both charge and excitons. To circumvent the limitations of carbazole-based hosts, we have studied a series of ultrawide energy gap hosts (UGHs). The materials have large HOMO to lowest unoccupied molecular orbital energy gaps, and triplet energies greater than that of carbazole. The authors present a class of small-molecule-based UGH materials applicable to vacuum-deposited OLEDs. They discuss the material design, and present device data for OLEDs employing four different UGHs. In addition, they show that high device efficiencies can be achieved in structures where the dopant conducts both holes and electrons in the EML.