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Device Engineering and Degradation M...
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ProQuest Information and Learning Co.
Device Engineering and Degradation Mechanism Study of All-Phosphorescent White Organic Light-Emitting Diodes.
紀錄類型:
書目-語言資料,手稿 : Monograph/item
正題名/作者:
Device Engineering and Degradation Mechanism Study of All-Phosphorescent White Organic Light-Emitting Diodes./
作者:
Xu, Lisong.
面頁冊數:
1 online resource (160 pages)
附註:
Source: Dissertation Abstracts International, Volume: 78-08(E), Section: B.
標題:
Materials science. -
電子資源:
click for full text (PQDT)
ISBN:
9781369660135
Device Engineering and Degradation Mechanism Study of All-Phosphorescent White Organic Light-Emitting Diodes.
Xu, Lisong.
Device Engineering and Degradation Mechanism Study of All-Phosphorescent White Organic Light-Emitting Diodes.
- 1 online resource (160 pages)
Source: Dissertation Abstracts International, Volume: 78-08(E), Section: B.
Thesis (Ph.D.)--University of Rochester, 2017.
Includes bibliographical references
As a possible next-generation solid-state lighting source, white organic light-emitting diodes (WOLEDs) have the advantages in high power efficiency, large area and flat panel form factor applications. Phosphorescent emitters and multiple emitting layer structures are typically used in high efficiency WOLEDs. However due to the complexity of the device structure comprising a stack of multiple layers of organic thin films, ten or more organic materials are usually required, and each of the layers in the stack has to be optimized to produce the desired electrical and optical functions such that collectively a WOLED of the highest possible efficiency can be achieved. Moreover, device degradation mechanisms are still unclear for most OLED systems, especially blue phosphorescent OLEDs. Such challenges require a deep understanding of the device operating principles and materials/device degradation mechanisms.
Electronic reproduction.
Ann Arbor, Mich. :
ProQuest,
2018
Mode of access: World Wide Web
ISBN: 9781369660135Subjects--Topical Terms:
557839
Materials science.
Index Terms--Genre/Form:
554714
Electronic books.
Device Engineering and Degradation Mechanism Study of All-Phosphorescent White Organic Light-Emitting Diodes.
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Source: Dissertation Abstracts International, Volume: 78-08(E), Section: B.
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Advisers: Ching W. Tang; Lewis J. Rothberg.
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Thesis (Ph.D.)--University of Rochester, 2017.
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As a possible next-generation solid-state lighting source, white organic light-emitting diodes (WOLEDs) have the advantages in high power efficiency, large area and flat panel form factor applications. Phosphorescent emitters and multiple emitting layer structures are typically used in high efficiency WOLEDs. However due to the complexity of the device structure comprising a stack of multiple layers of organic thin films, ten or more organic materials are usually required, and each of the layers in the stack has to be optimized to produce the desired electrical and optical functions such that collectively a WOLED of the highest possible efficiency can be achieved. Moreover, device degradation mechanisms are still unclear for most OLED systems, especially blue phosphorescent OLEDs. Such challenges require a deep understanding of the device operating principles and materials/device degradation mechanisms.
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This thesis will focus on achieving high-efficiency and color-stable all-phosphorescent WOLEDs through optimization of the device structures and material compositions. The operating principles and the degradation mechanisms specific to all-phosphorescent WOLED will be studied.
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First, we investigated a WOLED where a blue emitter was based on a doped mix-host system with the archetypal bis(4,6-difluorophenyl-pyridinato-N,C2) picolinate iridium(III), FIrpic, as the blue dopant. In forming the WOLED, the red and green components were incorporated in a single layer adjacent to the blue layer. The WOLED efficiency and color were optimized through variations of the mixed-host compositions to control the electron-hole recombination zone and the dopant concentrations of the green-red layers to achieve a balanced white emission.
520
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Second, a WOLED structure with two separate blue layers and an ultra-thin red and green co-doped layer was studied. Through a systematic investigation of the placement of the co-doped red and green layer between the blue layers and the material compositions of these layers, we were able to achieve high-efficiency WOLEDs with controllable white emission characteristics. We showed that we can use the ultra-thin co-doped layer and two blue emitting layers to manipulate exciton confinement to certain zones and energy transfer pathways between the various hosts and dopants.
520
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Third, a blue phosphorescent dopant tris[1-(2,6-diisopropylphenyl)-2-phenyl-1H-imidazole]iridium(III) (Ir(iprpmi)3) with a low ionization potential (HOMO 4.8 eV) and propensity for hole-trapping was studied in WOLEDs. In a bipolar host, 2,6-bis(3-(carbazol-9-yl)phenyl)-pyridine (DCzPPy), Ir(iprpmi)3 was found to trap holes at low concentrations but transport holes at higher concentrations. By adjusting the dopant concentration and thereby the location of the recombination zone, we were able to demonstrate blue and white OLEDs with external quantum efficiencies over 20%. The fabricated WOLEDs shows high color stability over a wide range of luminance. Moreover, the device lifetime has also been improved with Ir(iprpmi)3 as the emitter compared to FIrpic.
520
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Last, we analyzed OLED degradation using Laser Desorption Time-Of-Flight Mass Spectrometry (LDI-TOF-MS) technique. By carefully and systematically comparing the LDI-TOF patterns of electrically/optically stressed and controlled (unstressed) OLED devices, we were able to identify some prominent degradation byproducts and trace possible chemical pathways involving specific host and dopant materials.
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