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A Study Of Influence On OLED Output Efficiency Of Anode And Microcavity Effect

Posted on:2013-09-05Degree:MasterType:Thesis
Country:ChinaCandidate:L DingFull Text:PDF
GTID:2248330371988001Subject:Power electronics and electric drive
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Organic Light-Emitting Diode(OLED) has extensive advantages for nextgeneration displays, such as self emission, full color, low power consumption,light weight, high flexibility, et al. Thus, they are sometimes honored as the“Illusion Displays” or “Gorgeous Displays”. Because the OLEDs can bemanufactured easily, many display factories and research groups are investing intheir application areas. At present, the success of small OLED display panels formobile phone, watch, et al. Has become a threat for the market of small LCDdisplays.In this study of OLED with micro-cavity structure type, there are three mainelements to constitute microcavity OLED: first, two parallel cathode and anodewith reflectivity. Second, a microcavity resonator between two electrodes, that isstack organic layers. Third, light source within microcavity OLED. In this thesis,we adopt bottom emitting OLED with micro-cavity structure type, and modifythe thickness of HIL according to the results of simulation based on Fabry-Perotoptical model.This paper is major from the anode structure of the devices withmicrocavity theory to study how to improve the performance of OLEDs. thework includes four parts as follows:(1) A novel anode structure of OLED was fabricated by inserting amolybdenum trioxide (MoO3) layer into the interface of hole injectionlayer(HIL)1,4,5,8,9,11-hexaazatriphenylene–hexacarbonitrile(HAT-CN) andhole transport layer (HTL)4,4'-bis[N-(1-naph thyl)-N-phenylamino] biphenyl(NPB). The microcavity OLED with a150nm-thick Al top cathode and atransparent Al bottom anode on a glass substrate was fabricated. It has theconfiguration of Glass/Al(15nm)/HAT-CN(10nm)/MoO3(xnm)/NPB(30nm)/Alq3(70nm)/LiF(1nm)/Al(150nm)。The current density-voltage–luminance (J-V-L)performances shows that this structure is beneficial to the reduction of the driving voltage and the enhancement of the luminance.“hole only”devices werefabricated to verify the enhancement of hole injection and transport properities ofthis structure. The optical characteristics of the microcavity, such as narrowedand peak shift, were examined. We used Bphen replaced by Alq3as electrontransport layer, adjusted the thickness of Bphen. The highest luminance of thedevice is reached to15128cd/m2at13V, with a turn on voltage of3.0V. Theluminance efficiency is increased by nearly three times with introduction Bphenas electron transport layer (ETL) compared to Alq3. The improvement is ascribedto the step barrier theory and tunnel theory.(2) We report Al/MoO3thin film as a complex anode in high-performanceOLEDs. The unique efficacy of the device was found to result from enhancedinjection of holes into commonly used hole-transporting molecules due to a largereduction in the interface dipole at the anode/organic interface. Combined withthe enhanced EL emission as a result of a strong cavity effect, Due to the ease ofprocessing of Al/MoO3we successfully demonstrated large-area flexible OLEDson plastic substrates with uniform emission.(3) The sky-blue phosphor FIrpic-based electrophosphorescent bottom-emitting OLED employed a structure of Glass/Al(15nm)/MoO3(xnm)/NPD(40nm)/mCP:FIrpic(30nm,7%)/BCP(20nm)/Alq3(20nm)/LiF(1nm)/Al(150nm), usingMoO3and LiF as efficient hole and electron injection layers respectively. Thecavity structure was construed of the highly reflective Al cathode and thesemitransparent Al anode. Emission spectrum of the microcavity OLED centeredat468nm with a full width at half maximum (FWHM) of24nm, CIE colorcoordinates of x=0.14and y=0.15.indicating that the spectrum was modulatedand narrowed. Theoretical simulation of the enhancement factor of themicrocavity OLED is consisted with experiment result well.(4) we present a mechanism of carrier radiation distribution by the analysisof white organic electroluminescent device electroluminescent spectrum toexplain the regular pattern of carrier radiation distribution. It’s proved electronthat is injected from cathode is satisfied with regularity of radiation distributionon the organic emitting layer. This radiation distribution is related to severalfactors, such as electron injection capabilities, applied electrical field intensity,carrier mobility, et al.
Keywords/Search Tags:anode, OLED, microcavity, flexible, efficiency
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