Using an organic molecule with low triplet energy as a host in a highly efficient blue electrophosphorescent device.

To achieve high efficiencies in blue phosphorescent organic light-emitting diodes (PhOLEDs), the triplet energies (T1) of host materials are generally supposed to be higher than the blue phosphors. A small organic molecule with low singlet energy (S1) of 2.80 eV and triplet energy of 2.71 eV can be used as the host material for the blue phosphor, [bis(4,6-difluorophenylpyridinato-N,C(2'))iridium(III)] tetrakis(1-pyrazolyl)borate (FIr6; T1=2.73 eV). In both the photo- and electro-excited processes, the energy transfer from the host material to FIr6 was found to be efficient. In a three organic-layer device, the maximum current efficiency of 37 cd A(-1) and power efficiency of 40 Lm W(-1) were achieved for the FIr6-based blue PhOLEDs.