Performance And Research Of OLEDs Based On Ultrathin Blue Phosphorescent Material

Based on the luminescent properties of organic phosphorescent materials,this paper focuses on the influence of the traditional phosphorescent material FIrpic on the performance of the whole device when it is used as an ultra-thin layer instead of host guest doping system.In this paper,we design a new device which is based on FIrpic as ultra-thin layer.We compare the performance of several control groups to explore the rules,and study the transmission characteristics of hole and electron,the recombination region of exciton and the change of luminescence spectrum.The main exploration in this article are two materials:?tbt?₂Ir?acac?and FIrpic.The experimental part of this paper is divided into two parts.The first part is mainly related to the yellow phosphorescent dye:?tbt?₂Ir?acac?is investigated with a novel structure of ITO/MoO₃?5 nm?/NPB?40 nm?/TCTA?15 nm?/CBP:?tbt?₂Ir?acac??25nm?/Firpic?0.3 nm?/TPBi?35 nm?/Mg:Ag are fabricated.Based on this,five different doping concentrations of 3 wt.%,5 wt.%,7 wt.%,10 wt.%,13wt.%are chosen to analyze the influence of the?tbt?₂Ir?acac?doping concentration on the OLED.Adjusting the?tbt?₂Ir?acac?ratio of the emission layer,the performance of devices is changed.Among the five devices that we made in this experiment,device with x=10 wt.%doping ratio acquires the best performance,a high luminance of 41618 cd/m²,power efficiency of 49.7 lm/W,current efficiency of 67.3 cd/A,external quantum efficiency?EQE?of 18%,and a low efficiency roll-off at high luminance.Second step,the Ir complex FIrpic is investigated with a novel structure of ITO/MoO₃?5 nm?/NPB?40 nm?/TCTA?15 nm?/CBP:?tbt?₂Ir?acac??10 wt.%??25 nm?/FIrpic?y nm?TPBi?35 nm?/Mg:Ag,y=0,0.05,0.1,0.3,0.5,0.7.First of all,we give a brief account of the experimental scheme and rule discovery of FIrpic as a modified layer.The results show that phosphorescent material of FIrpic plays a significant role in improving YOLED performance,and the best performance is acquired at the thickness of 0.3 nm:a high luminance of 41618 cd/m²,power efficiency of 49.7 lm/W,current efficiency of 67.3 cd/A,external quantum efficiency?EQE?of 18%.The reason is the ultrathin FIrpic modification layer blocks excitons in EML.In the meantime,the high tripletenergy of FIrpic?2.75 eV?alleviates the exciton energy transport from EML to FIrpic.It is worth mentioning that the thickness of FIrpic in the device is thin,so it has not become a continuous film,but is similar to the material on the surface of CBP:?tbt?₂Ir?acac?.Finally,the TCTA is selected to be the electronic block layer between CBP:?tbt?₂Ir?acac?and FIrpic.Then,by adjusting the thickness of FIrpic,it is found that the performance of the device changes with increasing thickness,especially normalized spectrum.The test result shows that there is a huge difference in the device performance of different thickness of FIrpic.This phenomenon indicates that it's the ultra thickness of FIrpic as the blue emission layer that affects the device color.From the above experiments,we can see a conclusion:the ultra thickness of FIrpic can be used not only as a modification layer but also a emitting layer.