Top-emitting White Organic Light-emitting Diode Based On Phosphorescent Materials

Organic light-emitting device (OLED) technology shows tremendous business applications incommunication, information, display, and lighting. It is one of the most attractive projects inoptoelectronics informationfieldoverthelast decade.Generallyspeaking, organiclight-emittingdevice is to be a product that owns the market potential in next generation.Among many colorsof light source, white light is the most important of them because it can not only replace themodern fluorescent tube but also be backlight for liquid crystal displays and apply to full colortechnology. Hence, white OLED (WOLED) plays an important role in optoelectronicstechnology and the field of display. In this paper, we fabricate top-emitting WOLED based ontwo technologies of microcavity effect and out-coupling layer, at last study the characteristics ofthesedevices.Firstly,we designed the top-emittingWOLED based on microcavityeffect,use the metal- organic - metal micro cavity structural design microcavity. In order to complement redphosphorescent to produce white, 500 nm place is decided as the microcavity's resonant wavelength, we fabricated top-emitting WOLED based on microcavity effect through adjusting thethickness of different layers. The structure of the device is Ag (70 nm)/ MoO_x (3 nm)/m-MTDATA(25 nm)/ NPB (10 nm)/ Host: dopant (30 nm)/ BPhen (40 nm)/ Sm (5 nm)/ Ag(25nm), where the layer of CBPdoped with FIrpic and Ir(piq)2(acac) are employed as blue emittinglayer and red emitting layer, respectively. We fabricated two structure of phosphorescentWOLED: co-doped singleemittinglayer anddoubleemittinglayer,thenstudiedtheinfluenceoftheredandbluephosphorescent materialdopedindifferentpositionsonthedeviceperformance.This work laid the basis for the future use of microcavityeffects to fabricate high efficiencyandhighbrightnesstop-emittingWOLED。Inordertoimprovethethestatusoflowerefficiencyinthesecondchapter,then,top-emittingWOLED was fabricated by optimizing the thickness of ZnS layer with high refractive index inthevisibleregion,whichisusedasout-couplinglayer.Thenweoptimizedtheout-couplinglayerby the transmittivity formula of multilayer system, which was derived from Fresnel coefficientmatrix method. After Simulation, TOLED based on silicon with out-coupling layer of 122 nmand 0 nm (Contrasts device) thickness was fabricated. The structure of the device is Si/ Ag (70 nm)/ MoO_x (3 nm)/ m-MTDATA(25 nm)/ NPB (10 nm)/ CBP: 8% FIrpic (20 nm)/ CBP: 0.5%Ir(piq)2(acac) (10 nm)/ BPhen (40 nm)/ Sm (5 nm)/ Ag(25 nm)/ ZnS. The white light can beachieved by the structure of combining the blue phosphorescent and red phosphorescentmaterials. At last, we analyzed the influence of out-coupling layer's growth on devices'performance.CIE had been changed from(0.30,0.49) to (0.33,0.42) when we added 122 nm ZnSas out-coupling layer, and the device's brightness and the efficiency had the big improvement,reached 9213 cd/m2 and 3 cd/A, Than the device which not using the device ZnS antireflectioncoating increases 1.45 and 1.43 times. We could find that the CIE moved to the equal energypoint and got blue-shift with the voltage increasing. But the blue-shift was not obvious in theprocess ofanalyzingthespectrum bychangingangle. It illustratethat thedevicewefabricatedisvery suits in applying in the field of display area.