| 研究生: |
呂淮安 Lu, Huai-An |
|---|---|
| 論文名稱: |
以水/醇可溶性之含氮冠醚基芴衍生物為電子注入層製備高效率高分子發光二極體 Fabrication of Highly Efficient PLEDs Using Water/Alcohol-Soluble Fluorene Derivative Containing Azacrown Ether Groups as Electron Injection Layer |
| 指導教授: |
陳雲
Chen, Yun |
| 學位類別: |
碩士 Master |
| 系所名稱: |
工學院 - 化學工程學系 Department of Chemical Engineering |
| 論文出版年: | 2012 |
| 畢業學年度: | 100 |
| 語文別: | 中文 |
| 論文頁數: | 115 |
| 中文關鍵詞: | 高分子發光二極體 、電子注入層 、冠醚 |
| 外文關鍵詞: | PLED, crown ether, wet processes, electron-injection layer |
| 相關次數: | 點閱:103 下載:2 |
| 分享至: |
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高分子發光二極體(Polymer Light-Emitting Diode, PLED)是藉由從陽極與陰極注入電洞及電子,並在發光層中再結合,進而發出不同的光色,因此電荷注入及傳輸速率的平衡是影響發光效率最重要的因素。然而在大部分的有機共軛材料中,電洞通常比電子容易注入且有較好的傳輸能力,因此增進電子的注入與傳輸能力是提升PLED元件效率最有效的方法之一。許多研究利用低功函數金屬來提升電子的注入能力,然而低功函數金屬在大氣中的穩定性差,又必須以真空蒸鍍的方法來製備,成本高且不易控制其蒸鍍條件,因此可用濕式製程成膜的有機電子注入材料近年來蓬勃發展。
本研究合成含有三個含氮冠醚基團的芴衍生物FTC[51],並以FTC及含鹼金屬弱酸鹽類(M+)的FTC作為電子注入層,取代傳統的低功函數金屬,並以濕式製程(Spin-Coating)製備高效率高分子發光二極體。由於電子注入層的效果顯著,元件陰極只需以水、氧穩定的高功函數鋁金屬(Al)作為電極,即可達到高效率高分子發光二極體的目的。本研究選用的發光層有PF-Green-B與HY-PPV兩種,由能階上已可看出FTC具有電子注入與電洞阻隔的效果。其中以[FTC+碳酸鉀(K2CO3)]為電子注入層的元件有最好的效率表現。若以PF-Green-B為發光層,最大電流效率由無電子注入層的0.72 cd/A提升至21.58cd/A,約有30倍的提升;最大功率效率則由0.27 lm/W提升至12.42 lm/W,整整46倍的提升。若以HY-PPV為發光層,最大電流效率由無電子注入層的0.07 cd/A提升至6.93 cd/A,整整99倍的提升;最大功率效率則由0.03 lm/W提升至5.27 lm/W,約有177倍的提升。整體元件的效率、亮度均有顯著的提升,起始操作電壓亦有明顯的下降,達到高效率高分子發光二極體的目的。效率提升的原因推測為電子注入能力的提升與電洞阻隔的效果,本研究並以原子力顯微鏡、Hole-only元件、Electron-only元件、光伏打量測來證明各種使元件效率提升的假設。
To improve emission efficiency of polymer light-emitting diodes (PLEDs), we employed a water/alcohol-soluble fluorene derivative (FTC) having three terminal azacrown ether groups as electron-injection layer (EIL) to fabricate multi-layer PLEDs by spin-coating process. The results show that FTC or FTC plus M2CO3 (M: Na, K, Cs) are effective electron-injection layer for PLEDS with stable aluminum as cathode.
The structure of FTC was satisfactorily characterized by 1H NMR, COSY, NOESY, 13C NMR, FT-IR and elemental analysis. Its electrochemical properties were investigated by cyclic voltammetry (CV); the HOMO and LUMO levels were estimated to be -5.88 eV and -2.88 eV, respectively. Multi-layer PLEDs [ITO/PEDOT:PSS/EML/EIL/Al] were fabricated by wet process using two commercialized emitting materials (PF-Green-B or HY-PPV) as emission layer (EML) and FTC (or FTC in the presence of metal cations) as electron-injection layer (EIL). The insertion of the EIL enhances the device performance significantly. Particularly, the device using FTC plus K2CO3 as the electron-injection layer revealed the highest performance. For the devices based on PF-Green-B, the maximum luminance, maximum current efficiency and maximum luminous power efficiency were 17461 cd/m2, 21.58 cd/A, and 12.42 lm/W, respectively, which were superior to those without electron injection layer (1217 cd/m2, 0.72 cd/A, 0.27 lm/W). For the devices based on HY-PPV, the maximum luminance, maximum current efficiency and maximum luminous power efficiency were 10986 cd/m2, 6.93 cd/A, and 5.27 lm/W, respectively, which were also much higher than those without electron-injection layer. In addition, the turn-on voltages were also significantly reduced (from 5.7 V to 3.7 V, from 5.5 V to 2.5 V).
Electron-only and hole-only devices were fabricated to study the influence of the extra electron-injection layer. Insertion of EIL, whether it was neat FTC or FTC in the presence of M2CO3 (M: Na, K, Cs), results in great increase in electron current density and simultaneous reduction in hole current density. This will effectively raise the recombination ratio of electrons and holes because most conjugated emitting polymers (PF-Green-B or HY-PPV) are hole-transporting materials. Increased recombination ratio leads to enhanced emission efficiency. Moreover, they can be deposited by wet processes due to the solubility of FTC in mixture solvents of alcohol and water. Current results show that FTC and FTC plus M2CO3 are promising electron-injection materials for optoelectronic devices using aluminum as cathode.
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