Fabrication And Study Of White Organic Light-Emitting Devices

Organic light-emitting devices (OLEDs) have been attracting much attention due to their potential applications in flat-panel displays. Since Tang demonstrated the high brightness OLEDs at low operating voltage for the first time in 1987, materials and devices for OLEDs have developed rapidly.White organic light-emitting devices (WOLEDs) can be used not only white displays but also full color displays combined with color filters,backlights for liquid crystal displays (LCDs) and even illumination light sources. The research works in this field gained rapid development especially after 1994 when J. Kido reported the WOLEDs. In this thesis, we introduce some different structure WOLEDs with different materials and study the cha- racteristics and light-emitting theories of these devices.No-doped devices have many merits, such as simple technology, good repeat character. We fabricated the non-doped type WOLEDs using an ultra thin rubrene film and exciton blocker of NPBX. The devices have the following structure: ITO/2T-NATA(20nm)/ NPBX (25-d nm)/ rubrene(0.2nm) / NPBX (d nm)/DPVBi(30nm)/ Alq(30nm)/LiF(0.5nm)/Al. Because the NPBX is an effect electron blocking layer,the EL emission spectra of the devicesdepend on d.With an increase in d ,emission from DPVBi increased and emission from rubrene weakened .The CIE chromaticity coordinates of the devices change from (0.38,0.42) at 6V to (0.36,0.41) at 17V that are well within the white region. In the WOLEDs, a maximum luminance of 24170 cd/m~2 at applied voltage of 17V, a maximum luminous efficiency is 8.96cd/A at applied voltage of 6V.Usually, rubrene is used as a dopant. we fabricated the doped-type Multilayer WOLEDs using rubrene dopant. The devices have the following structure: ITO/2T-NATA(25nm)/ NPBX (20 nm)/ CBP:1%Rubrene(10nm)/ NPBX(5 nm)/DPVBi(32nm)/TPBi(20nm)/ Alq(10nm)/LiF(1nm)/Al. In the WOLEDs, a maximum luminance of 17770 cd/m2 with the CIE chromaticity coordinates (0.33,0.39) at applied voltage of 19V,a maximum luminous efficiency is 4.61cd/A at applied voltage of 10V. The CIE chromaticity coordinates of the devices is(0.33,0.39)without changing for luminance raging from 1000 cd/m2 to 17770 cd/m2 that are within the white center region.Highly efficient white phosphorescent organic light-emitting devices (WOLEDs) was fabricated using a phosphorescent sensitizer to excite a fluorescent dye,The device structure was ITO/2T-NATA(25nm)/ NPBX(25-dnm) /CBP:6%Ir(ppy)3:1% Rubrene(8nm)/NPBX(dnm) /DPVBi(30nm)/TPBi(20nm) /Alq(10nm)/LiF(1nm)/Al, where NPBX is N,N '-bis- (1-naphthyl)- N,N '–diphenyl -1, 1 '- biphenyl-4,4 '-diamine as a hole transporting layer and electron/exciton blocker, CBP is 4,4,N,N'-dicarbazolebiphenyl as host,DPVBi is 4,4 '-bis(2,2 -diphenyl vinyl)-1,1 '-biphenyl as blue fluorescent dye, rubrene is 5,6,11,12,-tetraphenylnaphthacene as fluorescent dye, Ir(ppy)3 is factris (2-phenylpyridine) iridium as phosphorescent sensitizer,and Alq is tris(8-hydroxyquinoline) aluminum as an electron-transporting layer. The WOLEDs has obtained white light emission by adjusting thickness of NPBX, when the concentration of Ir(ppy)3 is 6wt% and rubrene is 1wt%,respectively, the thickness of the doped emissive layer is 8nm. In the WOLEDs, a maximum luminous efficiency is 11.2cd/A with d is 10nm at applied voltage of 7V, a maximum luminance of 28170 cd/m2 at applied voltage of 17V, and The CIE chromaticity coordinates of the devices is (0.37,0.42), which in white region.