臺灣博碩士論文加值系統

本研究主要為製作高效率白光有機發光二極體元件 (WOLEDs)。我們主要選用兩種有機材料 C545T 和 TPBi 與一無機材料 NaF 分別插入由 NPB 有機材料為主的電洞傳輸層，並建立一具有多層量子井結構的白光有機發光二極體，如：NPB/C545T/NPB/C545T、NPB/TPBi/NPB/TPBi 或 NPB/NaF/NPB/NaF/NPB 等量子井結構。我們發現相較於未具有多層量子井結構的 WOLEDs，具有多層量子井結構的 WOLEDs 在元件效率上有明顯地提升。此元件效率的提升主要來自於電洞 - 電子注入量的平衡。
此論文主要分為兩部分，第一部分為研究分別利用 C545T、TPBi 和 NaF 三種材料所建立的多層量子井結構在不同層數的量子井與不同厚度下對元件光 – 電特性的影響。第二部分為主要探討利用紫外光能譜分析儀 (UPS) 和空間電荷限制電流法 (SCLC measurement) 來分析不用性質如在電洞傳輸層上的能階、遷移率、表面結構等變化，並進一步研究探討其電荷注入和傳輸機制以及對元件特性影響之原因。
由實驗結果發現：由紫外光能譜分析儀得知，分別將 C545T、TPBi、NaF 三種材料蒸鍍於 NPB 時，其兩種材料的介面之 HOMO 能帶會彎曲且形成量子井。由空間電荷限制電流法，我們可以發現具有量子井結構的單電洞元件上，其電洞的遷移率下降亦能有效地減少電洞的注入。因此，其電洞的注入量的減少而達到電洞 – 電子載子的平衡，進一步達到高效率白光有機發光二極體。其中，最佳元件在電流效率上有 216 % 的增進。

In this thesis, we focused on the fabrication with high efficiency white organic light-emitting diodes (WOLEDs). We adopted two organic materials, 2,3,6,7-Tetrahydro-1,1,7,7,-tetramethyl-1H, 5H,11H-10- (2-benzothiazolyl)quinolizino[9,9a,1gh]coumarin (C545T), 2,2',2" -(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi), and one inorganic material, NaF , to insert into NPB, respectively, forming the multiple quantum-well-like (MQW) structures consisting of the alternative layer of NPB/C545T/NPB/C545T, NPB/TPBi/NPB/TPBi or NPB/NaF/NPB/NaF. Compared with the current efficiency without MQW structure, that of the devices with MQW structure had been obviously improved. Such an improvement in the device performance is attributed to the improved hole-electron balance, which can be further attributed to the introduction of the MQW structure.
In the first part of this search, we reported the device with different materials, MQW number and thickness to investigate the optical and electrical characteristics of the OLEDs. At the second part, we used Ultraviolet Photoelectron Spectroscopy (UPS) and space-charge-limited current (SCLC) measurement to analyze various properties, like energy level, mobility, surface structure in HTL etc, and study the hole injection、transport mechanism and effects on the characteristics of the devices.
In this study, from UPS spectra, we found that evaporating C545T, TPBi, and NaF, respectively, on the NPB film would induce the shift of energy level at the organic material/NPB interface, and quantum wells were formed. The reduction of hole mobility in hole-only devices with quantum-well-like structures has been investigated by SCLC measurement. Therefore, the decreasing of hole injection was contributed to the reduction of hole mobility, which also achieved the hole-electron balance and demonstrated the highly-efficient white organic light-emitting diodes. Devices with the best device performance have 216 % improved in current density.

Table of Contents
List of Figures.................................. XII
List of Tables................................... XV

Content
Chapter 1...........................................1
1-1 Introduction.................................... 1
1-2 The Literature Review of MQWS................... 2
1-3 The Motivation of this Research................. 5
Chapter 2 Theory and Literature Review.............. 8
2-1 Basic Concepts of OLEDS......................... 8
2-1-1 Structures of OLEDS........................... 8
2-1-2 Principles of OLED Operation.................. 9
2-2 The Luminescent Principle of OLEDS.............. 11
2-2-1 Photoluminescence and Electroluminescence..... 11
2-2-2 Energy Transfer............................... 12
2-3 Carrier Injection............................... 13
2-4 Carrier Transport............................... 15
2-5 Materials of Anode and Cathode.................. 17
2-6 Emitting Layer.................................. 18
Chapter 3 Fabrication and Measurement Setups in OLEDS ................25
3-1 Thermal evaporating system...................... 25
3-2 Substrate cleaning procedures................... 26
3-3 The preparation of solution-processed emitting materials ............................................27
3-4 OLEDS configuration............................. 27
3-5 OLEDS fabrication............................... 28
3-6 Materials....................................... 29
3-7 Measurement of OLEDS characteristics............ 29
Chapter 4 Results and Discussion.................... 34
4-1 Part I: Fabricate Highly Pure WOLEDS............ 35
4-2 Part II: WOLEDS with C545T MQW Structures....... 41
4-3 Part III: WOLEDS with TPBI MQW Structures....... 50
4-4 Part IV: WOLEDS with NAF MQW Structures .........56
4-5 Part V：Space-charge-limited current (SCLC) Measurement ............................................63
4-6 Part VI：Ultraviolet Photoelectron Spectroscopy (UPS) Measurement......................................... 69
Chapter 5 Conclusions and Future Work............... 76
5-1 Conclusions..................................... 76
5-2 Future Work..................................... 77
Reference........................................... 78

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