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研究生： 黃世男
Huang, Shih-nan
論文名稱： 具備雙發光層結構之混成型共軛高分子白光發光二極體
Double Emission Layered White PLEDs based on Conjugated Polymers Blending
指導教授： 蘇炎坤
Su, Yan-kuin
學位類別： 碩士
Master
系所名稱： 電機資訊學院 - 電機工程學系碩士在職專班
Department of Electrical Engineering (on the job class)
論文出版年： 2009
畢業學年度： 97
語文別： 英文
論文頁數： 122
中文關鍵詞： 雙發光層結構 、高分子 、白光
外文關鍵詞： MEH-PPV, PFO_B, PFO_G, PLED
相關次數： 點閱：47  下載：1 
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    • 越簡單的製程代表良率的提升及成本的下降，故吾人於本論文中探討如何使用最簡易的製程技術及最基本的高分子發光材料，不摻雜高價或複雜的磷光錯合物Iridium，僅藉由雙層螢光材料發光結構來完成白光高分子聚合物發光二極體（WPLEDs）。
    然而雙層發光結構必然伴隨發生互溶的現象及光譜適當分配比率的問題。我們將在本論文中一併探討我們的處理方式及結果。
    首先，我們製作的有機高分子發光二極體是雙層結構，其結構為(ITO/PEDOT：PSS/Emission layer/Ca/Al)。其中以導電薄膜PEDOT：PSS 為電洞傳輸層(HTL)；Emission layer為各種不同濃度比率之橘（MEH-PPV）、綠(PFO_G)、藍(PFO_B) 高分子發光材料；而Ca和Al則分別為陰極。我們將先找出橘、綠、藍高分子發光材料各自的最佳參數，再進行雙層發光結構的濃度及比率最佳化，並找出減緩互溶現象的方法，我們使用掃瞄式電子顯微鏡（Scanning Electron Microscope；SEM）及EL光譜來確認雙層發光結構的完整性。
    經一連串的實驗調整後，在特定的製程條件下，我們得到純白光(0.33,0.33) 的最佳材料比例參數為 PFO-G 0.5 % (4) : MEH-PPV 1 % (1) / PFO-B 4 % ；最大亮度為3,256 cd/m2@9 V, 最大效率為0.19 cd/A@9 V。

    We will discuss an easily technology to fabricate WPLED by conjugated polymer materials without any expansive or complicated complex phosphorescence material as Iridium. The devices fabricated with the structure of the double emission layer are able to achieve the white light emission.
    However the structure of double emission layers suffered two problems that the mutual dissolving phenomenon and the suitable distribution of EL spectra by polymer blend ratio. We will discuss our method and resultant for those problems in this study.
    Firstly we fabricated the PLEDs with the double emission layers that the structure is as ITO / PEDOT : PSS / Emission layer / Ca / Al. The PEDOT : PSS was used as the hole transport layer (HTL) and the emission layer are formed by using various concentration and blend ratio of conjugated polymer materials such as Orange light-emitting material (MEH-PPV), Green light light-emitting material (PFO_G) and Blue light light-emitting material (PFO_B) and spin-coating. Ca and Al were used as cathode.
    In the experiment, we have to find out the optimal concentration of each conjugated polymer material. Then find out a method to decrease the mutual dissolving and optimize the concentration and blend ratio in the structure of the double emission layers. Here we confirmed the structure by SEM and EL spectrum.
    Finally, we got a device possessing the white light-emission with CIE coordinates of (0.33, 0.33), maximum luminance of 3,256 cd/m2 at 9 V and maximum efficiency of 0.186 cd/A at 9 V.

    Abstract (Chinese) …………………………………………………I Abstract ……………………………………………………………III Acknowledgment (Chinese) ……………………………………… V Contents …………………………………………………………… VI Figure and Table captions ……………………………………… X Chapter 1 Introduction 1-1 Organic Light-Emitting Diodes …………………………… 1 1-1-1 Materials for OLEDs ……………………………………… 2 1-1-1-1 Materials of Small molecules ……………………… 3 1-1-1-2 Materials of Polymers ………………………………… 3 1-1-2 Mechanisms of Light Emission ………………………… 4 1-1-2-1 Singlet state …………………………………………… 5 1-1-2-2 Triplet state …………………………………………… 5 1-1-2-3 Mechanism of photoluminescence …………………… 6 1-1-2-4 Electroluminescence in Inorganic LEDs …………… 7 1-1-2-5 Electroluminescence in Oganic LEDs ……………… 7 1-1-3 Cell configuration of OLEDs …………………………… 8 1-1-4 Degradation of OLEDs …………………………………… 9 Chapter 2 Operation principle of Polymer LED 2-1 Structure of Polymer LED ………………………………… 15 2-2 Interface between Polymer and Metal ………………… 16 2-3 Conduction in Polymer Thin Film ……………………… 17 2-4 Device efficiency ………………………………………… 17 2-4-1 Internal quantum efficiency ………………………… 18 2-4-2 External quantum efficiency ………………………… 21 2-4-3 Luminous (power) efficiency (ηp) and luminous efficiency (ηv) ………………………………………………… 23 Chapter 3 Experiment procedures 3.1 The Materials ……………………………………………… 26 3-1-1 ITO ………………………………………………………… 26 3-1-2 PEDO:PSS …………………………………………………… 26 3-1-3 MEH-PPV …………………………………………………… 27 3-1-4 PFO_G ……………………………………………………… 28 3-1-5 PF_B ………………………………………………………… 28 3-2 Device Structure …………………………………………… 29 3-2-1 Anode ……………………………………………………… 29 3-2-2 Hole transporting layer …………………………………30 3-2-3 Active layer (Double Emission layer) ……………… 31 3-2-4 Cathode …………………………………………………… 33 3-3 Device fabrication ………………………………………… 34 3-3-1 ITO pattern ……………………………………………… 34 3-3-2 Clean ITO substrate …………………………………… 36 3-3-3 Spin coating PEDOT:PSS layer ………………………… 36 3-3-4 Spin coating active layer …………………………… 37 3-3-5 Deposit electrode ……………………………………… 38 3-4 Device measurement ………………………………………… 39 3-4-1 Current – Voltage (I-V) characteristic ………… 39 3-4-2 Optical measurement …………………………………… 39 3-4-2-1 Photoluminescence …………………………………… 39 3-4-2-2 Electroluminescence ………………………………… 41 3-4-2-3 Luminescence - Current ……………………………… 41 3-4-3 Appearance measurement ………………………………… 42 3-4-3-1 AFM ……………………………………………………… 42 3-4-3-2 SEM ……………………………………………………… 44 3-4-3-3 Contact angle ………………………………………… 45 Chapter 4 Results and Discussion 4.1 Preamble ……………………………………………………… 61 4-2 Part I : analysis of basic devices …………………… 62 4-2-1 Characteristic of PFO_G ……………………………… 62 4-2-2 Summary of part I ……………………………………… 65 4-3 Part II : single layer device with blend polymer … 66 4-3-1 Characteristic of MEH-PPV …………………………… 66 4-3-2 Rough tuning the blend ratio in the single emission layer ……………………………………………………………… 67 4-3-3 fine tuning the blend ratio in the single emission layer ……………………………………………………………… 69 4-3-4 Summary of part II ……………………………………… 71 4-4 Part III:the white PLEDs with double emission layer 72 4-4-1 Characteristic of PFO_B ……………………………… 72 4-4-2 About of mutual dissolving …………………………… 74 4-4-3 Tune the concentration of PFO_B in 2nd emission layer ……………………………………………………………… 75 4-4-4 Tune the blend ratio of 1st emission layer for WPLED ……………………………………………………………………… 77 4-4-5 Summary of part III …………………………………… 80 4-5 The characteristic of white PLED ……………………… 81 4-5-1 The characteristic of device III-D ………………… 81 4-5-2 Summary of device III-D ……………………………… 85 Chapter 5 Conclusion ………………………………………… 117 Chapter 6 Future work ………………………………………… 118 Reference ………………………………………………………… 119 Figure and Table captions Fig. 1-1 Molecular structure of small organic materials (a), and polymer materials (b), commonly used in OLED …………………………………………………………………………11 Fig. 1-2(a) Singlet state ………………………………………12 Fig. 1-2(b) Triplet state ………………………………………12 Fig. 1-3 Jablonski energy level diagram ……………………12 Fig. 1-4 Electron transition in semiconductor: (a) direct transition, (b) indirect transition (Streetman et al., 2000) …………………………………………………………………13 Fig. 1-5 Mechanism of electroluminescence in organic light-emitting diodes ……………………………………………………13 Fig. 1-6 Some typical cell structure of OLEDs (Nalwa et al., 2003) ………………………………………………………… 14 Fig. 2-1 Spin-coating process …………………………………25 Fig. 3-1: the chemical structure of PEDOT and PSS ………46 Fig. 3-2 the chemical structure of MEH-PPV ……………… 47 Fig 3-3 absorption and emission spectra of MEH-PPV film in THF solution ……………………………………………………… 47 Fig. 3-4 the chemical structure of PFO_G ………………… 48 Fig. 3-5 the absorption and emission spectra of PFO_G film on ITO glass ……………………………………………………… 48 Fig. 3-6 the chemical structure of PF_B ……………………49 Fig. 3-7 the absorption and emission spectra of PF_B film on ITO glass ……………………………………………………… 49 Fig. 3-8 the structure of the device ……………………… 50 Fig. 3-9 Energy band of MEH-PPV ………………………………51 Fig. 3-10 flow chart of fabrication process ………………52 Fig. 3-11 the equipment of spin coating photo-resist … 52 Fig. 3-12(a) shows the patterned ITO glass before cutting …………………………………………………………………………53 Fig. 3-12(b) shows the patterned ITO glass after cutting …………………………………………………………………………53 Fig. 3-13 UVO-cleaner ……………………………………………54 Fig. 3-14 ITO cleaning processed …………………………… 54 Fig. 3-15 Surcoder (α - step) ……………………………… 55 Fig. 3-16 FE-SEM 7001 ……………………………………………55 Fig. 3-17 the hot plate …………………………………………56 Fig. 3-18 Glove box ………………………………………………56 Fig. 3-19 the equipment of Physical Vapor Deposition … 57 Fig. 3-20 Keithley 4200A ……………………………………… 58 Fig. 3-21 the PL measurement arrangement ………………… 58 Fig. 3-22 AFM (NT-MDT P7LS) ……………………………………59 Fig. 3-23 A drop of water on (a) hydrophilic (b) hydrophobic film ………………………………………………… 60 Fig. 3-23(c) Contact angle measurement …………………… 60 Fig. 4-1(a) The EL spectra of RGB material ……………… 86 Fig. 4-1(b) The Abs. intensity of RGB material ………… 86 Fig. 4-2(a) The structure of device I ………………………87 Fig. 4-2(b) The energy level graph of device I ………… 87 Fig. 4-3(a) The IV curve of device I with different concentration ………………………………………………………88 Fig. 4-3(b) the luminance and (c) EI curve of device I with different concentration ………………………………… 88 Fig. 4-4(a) The IV curve of device I with different spin speed …………………………………………………………………89 Fig. 4-4(b) the luminance and (c) EI curve of device I with different spin speed ………………………………………89 Fig. 4-5(a) The IV curve of device I with different baking temperature …………………………………………………………90 Fig. 4-5(b) The luminance and (c) EI curve of device I with different baking temperature ……………………………90 Fig. 4-6(a) The structure of device II-A ………………… 91 Fig. 4-6(b) The energy level graph of device II-A ………91 Fig. 4-7(a) The IV curve of device II-A with different concentration ………………………………………………………92 Fig. 4-7(b) The Luminance and (c) EI curve of device II-A with different concentration ………………………………… 92 Fig. 4-8(a) The structure of device II-B ………………… 93 Fig. 4-8(b) The energy level graph of device II-B ………93 Fig. 4-9(a) The EL spectra of blend ratio on 1:1 ……… 94 Fig. 4-9(b) The EL spectra of blend ratio on 29:1 ………94 Fig. 4-9(c) The EL spectra of blend ratio on 49:1 ………95 Fig. 4-9(d) The EL spectra of blend ratio on 69:1 ………95 Fig. 4-10 CIE chromaticity diagrams of various blend ratio of PFO_G and MEH-PPV …………………………………………… 96 Fig. 4-11 EL spectra and CIE chromaticity diagrams of various concentrations at MEH-PPV fixed on 1% ……………97 Fig. 4-12(a) The IV curve of device II-C with different concentration ………………………………………………………98 Fig. 4-12(b) The Luminance and (c) EI curve of device II-C with different concentration ………………………………… 98 Fig. 4-13(a) The structure of device III-A ……………… 99 Fig. 4-13(b) The energy level graph of device III-A ……99 Fig. 4-14(a) The IV curve of device III-A with different concentration …………………………………………………… 100 Fig. 4-14(b) The Luminance and (c) EI curve of device III-A with different concentration ………………………………100 Fig 4-15 the images of single and double emission layer by SEM ………………………………………………………………… 101 Fig 4-16 EL spectra including three complete peaks ……101 Fig. 4-17(a) The structure of device III-B ………………102 Fig. 4-17(b) The energy level graph of device III-B … 102 Fig. 4-18(a) The EL spectra of device III-B …………… 103 Fig. 4-18(b) the CIE chromaticity diagrams of the device III_B ……………………………………………………………… 103 Fig. 4-19 The I-V curve of single emission layer with 5% concentration of PFO_B …………………………………………104 Fig. 4-20 The CIE chromaticity diagram of Device III-C with various blend ratios …………………………………… 104 Fig. 4-21 The EL spectra of device III-C with various blend ratios ………………………………………………………105 Fig. 4-22(a) The EL spectrum of device with blend ratio of 49:1 (non-normalized) ………………………………………… 105 Fig. 4-22(b) The EL spectrum of device with blend ratio of 7:1 (non-normalized) ……………………………………………106 Fig. 4-22(c) The EL spectrum of device with blend ratio of 4:1 (non-normalized) ……………………………………………106 Fig. 4-23(a) The I-V curve of device III-D with 2% concentration …………………………………………………… 107 Fig. 4-23(b) The L-V curve of device III-D with 2% concentration …………………………………………………… 107 Fig. 4-23(c) The E-I curve of device III-D with 2% concentration …………………………………………………… 108 Fig. 4-23(d) The CIE diagram of device III-D with 2% concentration …………………………………………………… 108 Fig. 4-24(a) The I-V curve of device III-D with 3% concentration …………………………………………………… 109 Fig. 4-24(b) The L-V curve of device III-D with 3% concentration …………………………………………………… 109 Fig. 4-24(c) The E-I curve of device III-D with 3% concentration …………………………………………………… 110 Fig. 4-24(d) The CIE diagram of device III-D with 3% concentration …………………………………………………… 110 Fig. 4-25(a) The I-V curve of device III-D with 4% concentration …………………………………………………… 111 Fig. 4-25(b) The L-V curve of device III-D with 4% concentration …………………………………………………… 111 Fig. 4-25(c) The E-I curve of device III-D with 4% concentration …………………………………………………… 112 Fig. 4-25(d) The CIE diagram of device III-D with 4% concentration …………………………………………………… 112 Fig. 4-26 The EL spectra of devices with various concentration and spin speed …………………………………113 Table 4-1(a) the performance of device I …………………114 Table 4-1(b) the device I with different baking temperature ……………………………………………………… 114 Table 4-2 the Device II-C with different concentration 115 Table 4-3 the Device III-A with different concentration115 Table 4-4 the Device III-D with various concentration and spin speed …………………………………………………………116

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