Highly efficient phosphorescent organic light-emitting diodes using a beryllium metal–chelate complex as electron-transporting host material

A classical fluorescent metal–chelate complex bis(2-(2-hydroxyphenyl)-pyridine)beryllium (Bepp₂) has been used as an efficient electron-transporting host material to construct highly efficient phosphorescent organic light-emitting diodes (PHOLEDs) with an orange-emitting phosphorescent guest bis(7,8-benzoquinolinato) iridium (III) (N,N′-diisopropyl-benzamidine) ((bzq)₂Ir(dipba)). Due to the well-matched energy levels of Bepp₂ with the corresponding hole-/electron- transporting (HT/ET) materials and the high-efficiency and complete energy transfer of this host–guest system, the Bepp₂-based PHOLEDs exhibit rather low driving voltage (2.8 V) and high peak EL efficiencies of over 70 cd A⁻¹ for luminous efficiency, 55 lm W⁻¹ for power efficiency, and 23% for external quantum efficiency, a performance significantly better than that using CBP as the host.