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 (T 1 ) of host materials are generally supposed to be higher than the blue phosphors. A small organic molecule with low singlet energy (S 1 ) 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; T 1 =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.