Studies On Fluorescence/Phosphorescence Hybrid White Organic Light-Emitting Diodes Based On Aggregation-Induced Emission Materials

Recently,organic light-emitting diodes gains it success in panel display.For the characters of surface emitting,flexibility,flimsy,sunlight-like,low blue light,and no dazzle,white OLEDs?WOLEDs?exhibit a promising prospect in light-industry.Comparing to monochromatic light OLEDs,WOLEDs show more complicated device structure and more exciton quenching channels in light-emitting layer,so it exhibits larger roll-offs.Moreover,the stability of blue materials is curial to the lifetime and roll-off of devices.And there is still a long way for WOLEDs to be employed in light applications for the high price and low lifetime.Based on these issues,there are some requirements for OLED emitters.The first,the used device structures should be simple for low producing cost.The second,the used materials should have excellent electroluminescence performance such as high efficiency and low roll-off.The third,the electroluminescence of WOLEDs should achieve wide spectral coverage which will be sun light like and healthy.Due to the problems WOLEDs are facing,we find a promising choice which is using aggregation-induce emission?AIE?materials for WOLEDs.AIE materials have superiorities in solid-state emission which is very suitable for manufacturing of non-doped device.For the“paddle like”peculiarity of molecules,AIE materials have seldom exciton quenching channels.So that devices based on AIE materials have advantages of high efficiency and low roll-off.Here,three works about WOLEDs were developed based on AIE materials.1.A deep blue light molecule 3TPA-CN with AIE feature is introduced as blue emitter and phosphor host to fabricate WOLEDs.By optimizing the emission zones,high efficiency and low roll-off hybrid WOLEDs are achieved.The maximum forward-viewing power and external quantum efficiencies?PEs,EQEs?reach 86.7 lm W^-1 and 22.3%,and remain 59.2 lm W^-1 and 19.6%at the luminance of 1000 cd m^-2,commission Internationale de I'Eclairage?CIE?coordinates are measured to be?0.44,0.48?.By mechanism investigating,we find energy transfer is the main channel for light emitting,and carriers trapping process is the minor channel.Moreover,the exciton distribution could be regulated by emission zone design.And WOLEDs could be optimizated using this method.Furthermore,we set up a exciton distribution calculating method by mathematical modeling using monochromatic spectra.Based on multiple linear regression fitting,the ratio of emitting photons from reporting long-wavelength phosphors was caculated to represent exciton concentration.Such method exhibit a new and simple way for exciton concentration.2.We used a multifunctional deep blue AIE material TPB-AC,which can be used not only as excellent blue emitter,but also as good host of green/orange/red phosphors.A deep blue non-doped OLED with CIEy of 0.08 and high EQE of 7.0%is achieved(EQE_max=21.0%,27.3%,and 26.1%,EQE_1000nit=19.5%,25.9%,and 24.1%,respectively).Furthermore,a series of Ir?ppy?₂acac/Ir?tptpy?₂acac/Ir?dmdppr-dmp?₂?divm?phosphorescent OLEDs with high efficiency and low roll-off are obtained.Impressively,hybrid white OLEDs?WOLEDs?based on the deep blue AIEgen exhibit simultaneously high color rendering index?CRI>90?,excellent efficiency(EQE_max>25%,PE_max=99.9 lm W^-1 for two-color WOLEDs,PE_max=60.7 lm W^-1 for four-color WOLEDs),low roll-off(PE_1000nit=72.1 lm W^-1 for two-color WOLEDs,PE_1000nit=43.5 lm W^-1 for four-color WOLEDs)and superior stable color,indicative of the multi-function of AIEgens.Accordingly,this work opens a new direction for achieving high performance OLEDs,particularly offering a smart but simple way to depress the efficiency roll-off and reduce the cost of OLEDs for practical applications.3.Deep blue AIEgen TPB-AC and AIDF material CP-BP-PXZ are introduced as double non-doped layers in three-color WOLEDs.By inserting TCTA into these two non-doped films as interlayer to avoid exciton quenching process,a WOLED with high performance was obtained.The device exhibits a high maximum PE,and EQE of 50.5 lm W^-1,and 20.5%,respectively.And it shows a small roll-off at the luminance of 1000 cd m^-2(PE_1000nit=32.9 lm W^-1,EQE_1000nit=18.9%).Moreover,the CIE coordinates of this device are?0.52,0.45?with simultaneously a high CRI=90.Through the investigation of mechanism,we found that red phosphor Ir?dmdppr-dmp?₂?divm?prefer carriers trapping process to emit light,however,CP-BP-PXZ emits light through direct carriers recombination process and partial energy transfer from TPB-AC.And TPB-AC selects direct carriers recombination process to emit blue light.The developed WOLEDs with double non-doped layers feathers are generally suitable for AIE materials,and such simplified device structure also reduces costs of products.So it exhibits a promising prospective in the further.In our work,WOLEDs based on AIE materials show many excellent performance such as high efficiency,low roll-off,high stability and simplified structure.And AIDF materials with wide spectra can also improve CRIs of WOLEDs.Our research provides an promising answer of the problems which WOLEDs are facing in commercial applications.And it will promote WOLEDs using in light-indutry in the further.