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研究生：	黃彥棠 Huang, Yen-Tang
論文名稱：	純有機材料連接層用於串聯式有機發光二極體之研究 The study of a pure organic connecting layer for Tandem organic light-emitting diodes
指導教授：	蘇炎坤 Su, Yan-Kuin
學位類別：	碩士 Master
系所名稱：	理學院 - 光電科學與工程研究所 Institute of Electro-Optical Science and Engineering
論文出版年：	2008
畢業學年度：	96
語文別：	英文
論文頁數：	77
中文關鍵詞：	發光單元、純有機連接層、串聯式有機發光二極體、倒置結構元件、五環素、碳六十
外文關鍵詞：	EL unit, Pure organic connecting unit, Tandem OLED, Reverse device, Pentacene, C60
相關次數：	點閱：87 下載：2
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在本論文中，我們的有機電激發光二極體使用ITO玻璃為元件的基板，並採用真空熱蒸著技術成長元件。串聯式有機發光二極體的結構為ITO/ NPB/Alq3/C60/pentacene/NPB/Alq3/LiF/ Al。ITO為陽極，NPB為電洞傳輸層，Alq3作為綠光發光層和電子傳輸層， pentacene/C60 (五環素 / 碳六十)作為串聯式有機發光二極體結構中的純有機連接層，在倒置結構元件中插入連接層，對於此連接層施加逆偏壓下具有電荷產生的效果，並且注入鄰近的電子傳輸層、電洞傳輸層中，因此可增加電子與電洞於發光單元中再複合的數目而提高發光效率，另外LiF為緩衝層，Al為陰極，完成整個元件的製作。
本研究的目的在於找出最理想的連接層組合和連接層的最佳厚度。因為連接層在外加適當的操作電場下，主要是透過能帶彎曲、穿隧效應而使連接層中的電子脫離HOMO能帶，並在界面產生電子、電洞分離進而產生電荷，因為穿隧的過程和厚度有一定的關係，所以厚度對於電荷產生的效果具有ㄧ定的影響。由研究結果指出，以pentacene/C60這兩層厚度皆為10nm時候構成的連接層，具有最好的電荷產生效果，在操作電壓23volt時，讓Tandem結構的OLED效率以3.43cd/A相較於一般傳統元件2.57cd/A提升為一般傳統元件的1.338倍，亮度為1003cd/m2，CIE座標為(0.3067,0.5603)，此外在27volt時得到最大亮度6300 cd/m2，而pentacene/C60在元件電流密度在65 mA/cm2以下能使此Tandem OLED保持在最佳的運作狀態。

In this thesis, substrate for organic light-emitting diode was ITO-glass. Chemical vapor deposition technique was used for making all my devices. The multilayer structure of tandem OLED was ITO/ NPB/Alq3/C60/pentacene/NPB/Alq3/LiF/ Al. Here, ITO, NPB, Alq3, and pentacene/C60 were used as anode, hole-transporting layer, green light emitting layer/electron-transporting layer, and the connecting unit in the tandem OLED. When applying the reversed bias for the connecting unit, the charge generation phenomenon happened and injected into the adjoining electron-transporting layer and hole-transporting layer. So the recombination number of the electron-hole pair was increased and it raised the current efficiency in the device. In addition, lithium fluoride was used as a buffer layer and aluminum was the cathode.
The purpose of this thesis was to find a proper composition of the connecting unit and the optimum thickness of this connecting unit. As applying an electric field to the connecting unit, the charge generation was induced by the band bending and tunneling effect. That led the electrons to depart from the HOMO and leave the holes in the connecting unit. The tunneling process was associated with the thickness of the connecting unit so that charge generation also depended on it. The connecting unit consisted of 10nm-thick fullerene and 10nm-pentacene possessed the best effect of charge generation. When the operating voltage was at 23 volt, the tandem OLED achieved 3.43cd/A , that compared with the current efficiency of the conventional device (2.57cd/A) was raised 1.338 times. The luminance was 1003cd/m2，and CIE coordinate was located on (0.3067,0.5603). By the way, the maximum was 6300 cd/m2 at 27 volt bias. Pentacene/C60 connecting unit could work better in this tandem structure when the current density was lower than 65mA/cm2.

Content
Chinese Abstract.........................................I 
English Abstract........................................II 
Acknowledgement.........................................IV 
Content..................................................V 
Table Captions.........................................VII 
Figure Captions.......................................VIII 
Chapter 1 Introduction...................................1 
1-1 Development of organic light emitting diode..........1
1-2 Advantages of organic light emitting diode...........1 
1-3 The development of the tandem OLED...................2 

Chapter 2 Fundamental theory of organic light emitting 
        diodes...........................................5 
2-1 The varieties of the conventional organic light 
    emitting diodes......................................5 
2-2 The functional layers in the OLED....................6 
2-3 The working theory of OLED..........................12
        2-3-1 The absorption and emission of the 
        organic materials...............................12
        2-3-2 Fluorescence and Phosphorescence..........14 
        2-3-3 The emission process of OLED..............16
        2-3-4 The mechanism of the energy 
              transformation............................16
        2-3-5 The mechanism of exciplex and excimer 
              charge transfers..........................19
2-4 The efficiency of organic light emitting diode......19
        2-4-1 Quantum efficiency of OLED................20
        2-4-2 Power efficiency and luminous efficiency
              of OLED...................................21

Chapter 3 The properties and mechanism of tandem OLED...23
3-1 The characteristics of tandem OLED..................23
3-2 The mechanism of connecting layer...................23

Chapter 4 Experimental process and instruments..........30
4-1 The materials in my experiments.....................30 
4-2 The treatment of substrates.........................33
4-3 The deposition process..............................35
4-4 Measurement of the devices..........................38 

Chapter 5 Experimental results and discussion...........42
5-1 To optimize the thickness of every layer in
    conventional device.................................42
5-2 To prove the charge generation in my connecting
    layer...............................................52 
5-3 The adjustment in the thickness of connecting 
    layers..............................................57 
5-4 The transparency of my connecting layer..............64
5-5 Roughness analyzing of my connecting layer...........66

Chapter 6 Conclusion and future work.....................73

References...............................................74


Table captions
Table 1-1 The comparison with LCD and OLED................2
Table 1-2 The comparison between conventional OLED and 
          tandem OLED.....................................3
Table 3-1 Three kinds of connecting layers...............25
Table 4-1 The tooling conditions of the materials in 
          my experiment..................................35
Table 5-1 The CIE and wavelength peak of the devices 
          1~11 at the best current efficiency............47
Table 5-2 The CIE and wavelength peak of the devices
          12~15 at the best current efficiency...........51
Table 5-3 The Comparison of current efficiency between
          devices........................................58
Table 5-4 The root mean square roughness (Rq) and 
          average roughness (Ra) of samples 25~32........71

Figure captions
Fig. 2-1 The structures of various OLEDs..................6
Fig. 2-2 The model of electron-hole energy transformation system and process of electro-luminance..................13
Fig. 2-3 The process of charge carrier recombination in 
         energy band diagram.............................16
Fig. 2-4 The process of radiative energy transfer........17
Fig. 2-5 The process of Förster energy transfer..........18
Fig. 2-6 The process of Dexter energy transfer...........18
Fig. 2-7 Process of Exciplex charge transfers............19
Fig. 2-8 The scheme of charge carrier recombination and
         light emitting outside device...................28
Fig. 3-1 The tunneling effect of n-and p-doping layers...24
Fig. 3-2 Electronic diagram of connecting layer-The
         thermal stimulation model.......................26
Fig. 3-3 Electronic diagram of connecting layer-Doped
         organic/organic p-n junction case...............27
Fig. 3-4 Electronic diagram of connecting layer-Pure
         organic/organic case............................29
Fig. 4-1 Molecular Structure of NPB......................30
Fig. 4-2 Molecular Structure of Alq3.....................31
Fig. 4-3 Molecular Structure of C60......................31
Fig. 4-4 Molecular Structure of Pentacene................32
Fig. 4-5 Molecular Structure of LiF......................32
Fig. 4-6 Photolithography process for ITO substrates.....33
Fig. 4-7 Cleaning process for ITO substrates.............34
Fig. 4-8 Deposition process for OLEDs.................36-37
Fig. 4-9 Thermal CVD system..............................37
Fig. 4-10 Polychromator wavelength dispersion............39
Fig. 4-11 CIE 1931 Chromaticity Diagram..................40
Fig. 4-12 Measurement system.............................41
Fig. 5-1-1 The structures of the conventional devices with
           various thickness of NPB layer................43
Fig. 5-1-2 The I-V curve of the devices 1~11.............43
Fig. 5-1-3 The L-V curve of the devices 1~11.............44
Fig. 5-1-4 The current efficiency-current density curve 
           of the devices 1~11...........................44
Fig. 5-1-5 The leakage current of the devices 1~11.......45
Fig. 5-1-6 The EL Spectra of the devices 1~11 at the 
           best current efficiency.......................46
Fig. 5-1-7 The structures of the conventional devices 
           with various thickness of Alq3 layer..........48
Fig. 5-1-8 The I-V curve of the devices 12~15............48
Fig. 5-1-9 The L-V curve of the devices 12~15............49
Fig. 5-1-10 The current efficiency-current density curve
            of the devices 12~15.........................49
Fig. 5-1-11 The EL Spectra of the devices 12~15 at the
            best current efficiency......................52
Fig. 5-2-1 The structures of reverse device and another 
           one with a connecting layer...................52
Fig. 5-2-2 The energy level diagram of a reverse 
           structural device.............................52
Fig. 5-2-3 The energy level diagram of a reverse 
           structural device with a connecting layer.....53
Fig. 5-2-4 The double-insulation-type device with a 
           connecting layer for the capacitance  
           measurement...................................53
Fig. 5-2-5 (a) The characteristic of current density 
           versus voltage in linear coordinate type......55
Fig. 5-2-5 (b) The characteristic of current density 
           versus voltage in log coordinate type.........56
Fig. 5-3-1 The structural schemes of conventional device 
           and the tandem OLED...........................57
Fig. 5-3-2 The electric characteristic of these devices..59
Fig. 5-3-3 The luminance-voltage curve of these devices..59
Fig. 5-3-4 The current efficiency-current density curve 
           of these devices..............................60
Fig. 5-3-5 The luminance-current efficiency curve of 
           device 19 and device 20.......................60
Fig. 5-3-6 The EL spectra of device 19 and device 20.....61
Fig. 5-3-7 The CIE coordinate of device 19...............62
Fig. 5-3-8 The CIE coordinate of device 20...............63
Fig. 5-4-1 The structures of the devices for transparency
           measurement...................................64
Fig. 5-4-2 The transparency of samples 8~10..............65
Fig. 5-5-1 The samples for roughness analyzing...........66
Fig. 5-5-2 2D and 3D AFM images of sample 25.............67
Fig. 5-5-3 2D and 3D AFM images of sample 26.............67
Fig. 5-5-4 2D and 3D AFM images of sample 27.............68
Fig. 5-5-5 2D and 3D AFM images of sample 28.............68
Fig. 5-5-6 2D and 3D AFM images of sample 29.............69
Fig. 5-5-7 2D and 3D AFM images of sample 30.............69
Fig. 5-5-8 2D and 3D AFM images of sample 31.............70
Fig. 5-5-9 2D and 3D AFM images of sample 32.............70
                                    

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