Investigated OLED With QAD Sub-monalayer And White OLED With The Single-doped Layer Of Rubrene

Nowadays, the technique of information displays acts as the criticalinstrumentality for mankind obtaining information and the effects of FlatPanel Displays (FPDs) become more and more significant. As one of the mostimportant members of FPDs, the technique of organic light-emitting devices ordisplays (OLEDs) attracts worldwide attention in the fields of science andindustry due to its many merits of light weight, low cost, broad visual angle,high response speed, spontaneous light-emitting, high brightness andefficiency, etc.. In recent over ten years after C. W. Tang reported the highbrightness OLED at low operating voltage for the first time in 1987, itgradually becomes the international cutting-edge project and the focus ofinternational competitions which need the cooperation and research of manyintercrossed branch of science. By the application of novel materials, suitablestructures and process technologies, and also by the efforts of world knowncompanies, the performances of OLEDs are made significant improvementand almost reach to the level of commercialization.Currently, OLED consists of hole –transporting layer ( HTL), electron-transporting layer( ETL) and emissive layer ( EML). EML usually make up oftwo or more organic materials by co-doping. And doping is the most popularand the most important method for high-efficiency and stable OLEDs.However, people found that sub-monolayer emission also has the same result,Matsumura and Furukawa et al. inserted the rubrene sub-monolayer (0.05nmthick) at the interface of HTL and ETL in OLED, which can get better deviceperformance than doping method. In this thesis we investigated OLED with QAD sub-monolayer emission,since QAD is one of the typical representatives of another kind of organicemissive materials different from rubrene, whose emission depends onexcitons energy transfer from other organic material, but not capture carriersdirectly. Utilized ITO/NPB(60nm)/Alq3(xnm)/QAD(0.05nm)/Alq3[(60-x) nm]/LiF/Al device structure, we investigated the formation and emigration processof excitons in popular double-layer OLED using QAD sub-monolayer asexcitons probe, when x is 5nm, device achieves the highest brightness, itindicated that the energy transfer from Alq3 to QAD is best when QADsub-monolayer located at 5nm position from the NPB/Alq3 interface. In orderto improve the energy transfer from Alq3 to QAD, we also utilized BCP asexcitons and holes blocking layers, the optimum structure of OLED with QADsub-monolayer is ITO/NPB(60nm)/Alq3(5nm)/QAD(0.02nm)/Alq3(5nm)/BCP(8nm)/ Alq3(42nm) /LiF(0.5nm)/ Al, finally a maximum efficiency 7.2cd/A is obtained, and almost pure QAD emission without Alq3 spectrum isobserved.White organic light-emitting devices (WOLEDs) can be used not onlyas illumination lighting sources and backlights for LCD but also as full colorOLEDs combined with color filters. The research works in this fielddeveloped rapidly, especially after Kido firstly reported the WOLEDs in1994. In this thesis we investigated the performance and emission mechanismof WOLED with single rubrene-doped layer, WOLED structure was ITO/m-MTDATA(40nm)/NPB(10nm) /ADN:rubrene(30nm)/Alq3( 30nm)/LiF(0. 8nm)/Al, it had a simple structure compared with former reported WOLEDs.By changing the concentration of rubrene, we fabricated singlerubrene-doped layer WOLED with good brightness, efficiencies and CIE.When the concentration of rubrene is 0.5% ,device CIE is (0.31,0.34),very near the equal energy point of white light. The mechanism of incompleteenergy transfer and directly carriers capture by rubrene was existed in thisWOLED simultaneously.However, in this WOLED with single rubrene-doped layer, a "valley"always lies between the spectra of the two materials, because only twomaterials join in the emission process which limited the range of EL spectra. Ifthe holes can reach the interface between the doped layer and Alq3, they willinject into Alq3 layer easily, this will be followed by exciton formation andgreen light emission of Alq3. Finally the "valley" is filled. We choose theconcentration of rubrene is 0.5%, the optimum structure is: ITO/m-MTDATA(40nm) /NPB(10nm) /rubrene:ADN(25nm)/Alq3(35nm)/LiF(0.8nm)/Al, and WOLED CIE is improved to (0.30,0.36), and a maximumbrightness and efficiency with 19800cd/m2 and 4.7cd/A was achieved.