Research On The Effect Of Square Wave-Type Interfacial Structure On Electrophosphorescent Optical Performances Of The Device

In this paper, the effects of a new interface structure on electroluminescent performance were investigated on the basis of a typical phosphorescent OLED of ITO/NPB/CBP:Ir(ppy)3/BAlq/Alq3/LiF/Al. The square-wave structure was constructed at the NPB/CBP:Ir(ppy)3, CBP:Ir(ppy)3/BAlq and Alq3/LiF interfaces to research the effects of the thickness and the number of protrusions on the photoelectrical properties.The square waves were constructed at Alq3/LiF interface in order to study the effects of square-wave interface on photoelectrical properties.The devices with the protrusion thickness of 5nm, 1Onm,15nm,20nm, were fabricated respectively. Results show that the square wave shape at the BAlq/Alq3 interface can change the injection, transport of electrons and changes of electron-hole pairs distribution of on the light-emitting layer interface. We found that the D15-3 device with three protrusions and thickness of 15nm have the highest current efficiency of 28cd/A which was increased by 43% compared with the traditional devices.The effect of the number and thickness of protrusion on the optical properties were studied by fabricating the square wave at CBP:Ir(ppy)3/BAlq,BAlq/Alq3,Alq3/LiF.Therefore, the devices with the protrusion thickness of 2nm,4nm,6nm,8nm were prepared respectively. Experimental data suggest that the square wave at CBP:Ir(ppy)3/BAlq, BAl q/Alq3 interfaces can change not only the thickness of light-emitting layer of CBP:Ir(ppy)3, but also the interface structure of Alq3. Consquently the injection efficiency and the recombination probability of electrons were improved. Inaddition, the increasing number of light-emitting layer interface also result in the improved current efficiency. The device D4-3 with three protrusions and. thickness of 4nm displays the highest current efficiency of 27.8 cd/A, which was increased by 42% related to the traditional devices.The effects of the number and thickness of protrusion on the photoelectrical properties were studied by constructing the square wave at NPB/CBP:Ir(ppy)3,CBP:Ir(ppy)3/BAlq,BAlq/Alq3,Alq3/LiF interfaces. Thus, the devices with the thickness of 5nm,10nm,15nm,20nm were fabricated respectively. Results reveal that devices were divided into several parallel devices with different thickness of NPB. Its current density is lower than that of traditional ones with NPB thickness of 30nm. Secondly, the square-wave interface can enhance the areas of carrier recombination, disperse triplet-excitons at NPB/CBP:Ir(ppy)3 interface and reduce the probility of triplet exciton quenching. As a result, the triplet-triplet excitons radiative decay rate was increased. Finally, the square-wave-type interface was conducive to out-coupling the wave-guided light into the outside. Accordingly, the device D10-3 with three protrusions and thickness of 10nm show the highest current efficiency of 45 cd/A, which was increased by 64% by contrast with the traditional ones.