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完整後設資料紀錄
DC 欄位 | 值 | 語言 |
---|---|---|
dc.contributor.advisor | 吳志毅(Chih-I Wu) | |
dc.contributor.author | I-Wen Wu | en |
dc.contributor.author | 吳以雯 | zh_TW |
dc.date.accessioned | 2021-06-16T16:36:24Z | - |
dc.date.available | 2015-11-22 | |
dc.date.copyright | 2012-11-22 | |
dc.date.issued | 2012 | |
dc.date.submitted | 2012-10-18 | |
dc.identifier.citation | Chapter 1
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Paasch, Interfacial charges and electric field distribution in organic hetero-layer light-emitting devices. Organic Electronics, 2000. 1(1): p. 41-47. Chapter 6 1. Burrows, P.E., V. Bulovic, S.R. Forrest, L.S. Sapochak, D.M. McCarty, and M. E. Thompson, Reliability and degradation of organic light emitting devices. Applied Physics Letters, 1994. 65(23): p. 2922-2924. 2. Cao, Y., G. Yu, I.D. Parker, and A.J. Heeger, Ultrathin layer alkaline earth metals as stable electron-injecting electrodes for polymer light emitting diodes. Journal of Applied Physics, 2000. 88(6): p. 3618-3623. 3. Luo, Y., H. Aziz, Z.D. Popovic, and G. Xu, Degradation mechanisms in organic light-emitting devices: Metal migration model versus unstable tris(8-hydroxyquinoline) aluminum cationic model. Journal of Applied Physics, 2007. 101(3): p. 034510. 4. Kondakov, D.Y., J.R. Sandifer, C.W. Tang, and R.H. 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Brütting, Impedance spectroscopy as a probe for the degradation of organic light-emitting diodes. Journal of Applied Physics, 2010. 107(5): p. 054501. 10. Ehrenfreund, E., C. Lungenschmied, G. Dennler, H. Neugebauer, and N.S. Sariciftci, Negative capacitance in organic semiconductor devices: Bipolar injection and charge recombination mechanism. Applied Physics Letters, 2007. 91(1): p. 012112. 11. Noguchi, Y., N. Sato, Y. Tanaka, Y. Nakayama, and H. Ishii, Threshold voltage shift and formation of charge traps induced by light irradiation during the fabrication of organic light-emitting diodes. Applied Physics Letters, 2008. 92(20): p. 203306. | |
dc.identifier.uri | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/63350 | - |
dc.description.abstract | 本論文主要研究使用電流及阻抗對電壓特徵曲線來探討有機發光二極體元件內部特性,包含元件的起始電壓、載子傳輸層中的載子遷移率、以及陰極金屬或電子注入層擴散距離。
第一部分中,起始電壓定義為將電流取對數後在對電壓圖上的上升起始點,自起始電壓後元件開始導通電流。實驗結果發現有機發光二極體的起始電壓由電洞傳輸層的最高填滿軌域與電子傳輸層的最低未填滿軌域能階差決定,此能階差需考慮兩有機層間的真空能階位移。實驗中以紫外光光電子能譜分析儀觀察有機材料介面的實際能階圖。 此外,在元件導通前的阻抗轉折為另一研究主題,此阻抗轉折與兩載子傳輸層間的介面電荷相關。實驗結果顯示僅當電洞傳輸層中的電洞遷移率遠大於電子傳輸層中的電子遷移率時才會有此阻抗轉折發生,反之,當兩載子遷移率相差不大,阻抗僅在元件導通時下降。接著,將阻抗轉折處的電壓定義為轉折電壓,並探討轉折電壓與元件結構的關係。一般而言,轉折電壓由電子傳輸層厚度及介面電荷密度決定,但實驗發現在電子注入層的存在下,轉折電壓會往正向偏壓平移。由轉折電壓與電子傳輸層厚度關係推測,該平移是由於電子注入層或陰極金屬材料擴散進入電子傳輸層造成。根據以上推論,阻抗對電壓特徵曲線可用來初步比較兩載子傳輸層的載子遷移率關係並且以非破壞性的方式觀察元件內陰極材料擴散的情形。 | zh_TW |
dc.description.abstract | The electrical properties of organic light emitting diodes (OLEDs), including the turn-on voltage, carrier mobility, and diffusion length of cathode materials, are investigated by current density-voltage (J-V) and impedance-voltage (Z-V) characteristics in this dissertation.
First, the turn-on voltage, which is determined by the voltage where log J exhibits a sharp rise and the current starts to flow through the device, is demonstrated to be close to the difference between the highest occupied molecular orbital (HOMO) of the hole transport layer (HTL) and the lowest unoccupied molecular orbital (LUMO) of the electron transport layer (ETL), taking into consideration of the vacuum level shift analyzed by ultra violet photoelectron spectroscopy (UPS). Then the additional impedance transition before the device turns on is examined in the devices with several combinations of the carrier transport layers, and the results indicate that the impedance transition occurs only in the devices with the hole mobility in the HTL much greater than the electron mobility in the ETL. In addition, the further investigations of the transition voltages, defined as the voltage where the impedance drops to a lower value before the turn-on voltage, imply that the transition voltages shift to the positive voltage in the devices with the electron injection layer, which is inferred to correlate closely with the diffusion length of the cathode materials. Based on these assumptions, the Z-V characteristic is proposed as the potential methods to initially compare the carrier mobilities in the carrier transport layers and nondestructively observe the cathode diffusion length in the OLEDs. | en |
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dc.description.tableofcontents | Contents
誌謝 I 摘要 III Abstract IV Contents V Chapter 1. Introduction 1 1.1 Organic light emitting diodes (OLEDs) 1 1.1.1 Development and applications of OLEDs 1 1.1.2 Operation principles of OLEDs 3 1.2 Current conductions in OLEDs 6 1.2.1 Injection limited conduction 6 1.2.2 Bulk limited conduction 7 1.3 Impedance versus voltage characteristics 9 1.3.1 Electrical impedance 9 1.3.2 Impedance transition before the devices turn on 11 1.4 Motivation 16 1.5 Overview of this dissertation 17 Chapter 2. Experimental 20 2.1 OLED device processing 20 2.1.1 Device structures and sample preparation 20 2.1.2 Thermal evaporation 22 2.1.3 Device characterization 23 2.2 Photoelectron spectroscopy 24 2.2.1 Background of the photoelectron spectroscopy 24 2.2.2 Energy level analysis by ultra violet photoelectron spectroscopy (UPS) 25 2.2.3 Experimental set up of the photoelectron spectroscopy 27 Chapter 3. Correlation of turn-on voltage and energy band alignment in OLEDs 30 3.1 Background of the turn-on voltage 31 3.2 The devices with different organic layer thickness and electrodes 34 3.2.1 The devices with different organic layer thicknesses 34 3.2.2 The devices with different cathodes and electron injection layers 36 3.3 The devices with various electron transport layers 38 3.3.1 The J-V characteristics of devices with various electron transport layers 38 3.3.2 The energy band alignment of the carrier transport layers 40 3.4 Summary 45 Chapter 4. Correlations of impedance-voltage characteristics and carrier mobility in organic light emitting diodes 48 4.1 Survey of the carrier mobility evaluation in organic materials 49 4.1.1 Time of flight (TOF) 49 4.1.2 Time resolved electroluminescence (TREL) 51 4.1.3 Space charge limited current (SCLC) and dark-injection space charge limited current (DI SCLC) 52 4.1.4 Impedance spectroscopy (IS) 53 4.2 Experiment results and discussion 54 4.2.1 The devices with various cathodes 54 4.2.2 The devices with various electron transport layers 56 4.2.3 The devices with different combinations of organic materials 60 4.2.4 The devices with doped Alq3 layers 62 4.3 Evaluating the carrier mobility by the Z-V characteristics 64 4.4 Summary 66 Chapter 5. Investigation of the cathode material diffusion length in OLEDs through impedance characteristics 69 5.1 Introduction 70 5.1.1 The effects of the metal diffusion in OLEDs 71 5.1.2 Survey of the methods to analyze the metal diffusion in OLEDs 73 5.2 Experiments and discussion 75 5.2.1 The devices with different thicknesses of the ETLs 75 5.2.2 The devices with various cathode structures 77 5.2.3 The correlation between the transition voltage and the thickness of ETL 79 5.3 Summary 85 Chapter 6. The analysis of the degradation mechanisms in OLEDs via the impedance-voltage characteristics 88 6.1 Introduction to the degradation in OLEDs 88 6.1.1 Aging mechanisms in OLEDs 89 6.1.2 Methods to investigate the aging mechanisms in OLEDs 90 6.2 Devices with the electrical stress 91 6.2.1 Impedance-voltage (Z-V) characteristics as a function of time 91 6.2.2 Variation of the transition voltages after operation 95 6.3 Degradation from the exposure of the ultra-violet radiation 97 6.4 Summary and Future work 102 Chapter 7. Conclusion and future work 104 7.1 Conclusion 104 7.2 Future work 106 | |
dc.language.iso | en | |
dc.title | 以阻抗對電壓特徵曲線分析有機發光二極體載子傳輸及起始電壓特性 | zh_TW |
dc.title | Investigations of Carrier Transport and Turn-on Voltages in Organic Light Emitting Diodes via Impedance-Voltage Characteristics | en |
dc.type | Thesis | |
dc.date.schoolyear | 101-1 | |
dc.description.degree | 博士 | |
dc.contributor.oralexamcommittee | 吳育任,郭宗枋,孟心飛,余沛慈,冉曉雯 | |
dc.subject.keyword | 有機發光二極體,阻抗對電壓曲線,起始電壓,載子遷移率,陰極擴散長度, | zh_TW |
dc.subject.keyword | OLED,Z-V characteristics,turn-on voltage,carrier mobility,cathode diffusion length, | en |
dc.relation.page | 106 | |
dc.rights.note | 有償授權 | |
dc.date.accepted | 2012-10-19 | |
dc.contributor.author-college | 電機資訊學院 | zh_TW |
dc.contributor.author-dept | 光電工程學研究所 | zh_TW |
顯示於系所單位: | 光電工程學研究所 |
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