Highly efficient bilayer blue phosphorescent organic light-emitting devices

We have developed highly efficient blue phosphorescent organic light-emitting devices comprising of two organic layers. Hole transporting 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) was used as an emitting host for iridium(III)bis[(4,6-di-fluorophenyl)-pyridinato-N,C2′]picolinate (FIrpic) guest. In our bilayer system, the host–guest energy transfer process leads to a low optimal doping concentration of 2 wt%, while the better charge balance is achieved by the better electron injection into the host layer from electron transport layer. Using these bilayer structures, we demonstrate a maximum current efficiency of 34 cd/A in the device structure of ITO/TAPC: FIrpic (30 nm, 2 wt%)/3-(4-biphenyl-yl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole (50 nm)/LiF/Al.