Low doping white phosphorescent organic light-emitting diodes

Efficient white organic light-emitting diodes (OLEDs) based on a novel phosphorescent material (t-bt)2Ir(acac) with a structure ITO/CuPc (15 nm)/NPB (15 nm)/CBP : (t-bt)2Ir(acac) (30 nm, x%)/ BCP (20 nm)/Alq (20 nm)/LiF (1 nm)/Al (100 nm) were fabricated. (t-bt)2Ir(acac) lightly doped in a host material CBP was used as a yellow emitting layer and fluorescent material NPB was used as a blue emitting layer as well as a conventional hole transporting material. Low doping concentration (1%) device showing white light emission from 6 V to 14 V has a maximum efficiency 1.6 lm/W at 8 V and a maximum luminance of 4360 cd/m2 at 13 V. High doping concentration (2% and 5%) devices emit strong yellow light under low bias and change to white light emission above 10 V bias although they show higher efficiency and luminance than 1% doping concentration device.