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研究生：	張貿翔 Chang, Mau-Shang
論文名稱：	上發光型有機高分子發光二極體 Top-emitting Polymer Light-emitting Diodes
指導教授：	洪茂峰 Houng, Mau-Phon
學位類別：	碩士 Master
系所名稱：	電機資訊學院 - 微電子工程研究所 Institute of Microelectronics
論文出版年：	2006
畢業學年度：	94
語文別：	英文
論文頁數：	103
中文關鍵詞：	微共振腔、高分子發光二極體、上發光
外文關鍵詞：	top, microcavity, blue-shift, PLED
相關次數：	點閱：58 下載：3
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最近，有機高分子發光二極體(PLED)早已能有效的製作上發光型的結構。發光強度的提高和發光頻譜的窄化可以歸咎於微共振腔效應(microcavity effects) 。在本論文中，上發光型元件的結構為Glass/ITO/Ag(120nm)/
PEDOT:PSS(40nm)/DB-PPV/Ca(10nm)/Ag，而元件發光從陰極-鈣/銀(Ca/Ag) 那面通過。而發光的材料為DB-PPV(2,3-dibutoxy 1,4-poly(phenylene vinylene))被夾在兩層金屬電極中，一個電極為經過表面處理的下反射銀(Ag)陽極，另外一個電極為上半穿透雙層陰極-鈣/銀(Ca/Ag)，最後在正偏壓下光由半穿透的陰極發射出。藉由改變共振腔裡的有機高分子發光層厚度以及雙層金屬陰極中的銀厚度，可以同時獲得較窄的發光頻譜和發光強度的提高。經由有機高分子發光層厚度的適當調整以及濃度的搭配，我們普遍可以發現在濃度0.6%中轉速2000rpm(65nm)和濃度0.7%中4000rpm(58nm)的發光效率分別為最大，這歸咎於大部份的再結合放光區較靠近反節點(antinode)，因此元件的正向發光效率(luminance efficiency)分別在濃度0.6%中提高1.13 ~ 1.65倍(2.22~3.25cd/A)以及在濃度0.7%中提高1.01 ~ 1.79倍(1.68~2.99cd/A)。除此之外，單一發光層元件的發光波峰在頻譜範圍上有寬廣的變化，從522nm到622nm，歸咎於不同的DB-PPV厚度。因此，調變發光的顏色從原本的黃綠色(λD=560nm) 變為飽和綠色(λD=527nm) 以及黃橘色(λD=582nm)，而發光頻譜的半高寬(FWHM)更從原本的70nm左右減少到20nm左右。

Recently, polymer light-emitting diodes (PLEDs) have been significantly fabricated with top-emitting architecture. The emission intensity enhancement and narrowing electroluminescence (EL) spectrum can be attributed to microcavity effects. In this thesis, a top-emitting structure was Glass/ITO/Ag(120nm)/PEDOT:PSS(40nm)/DB-PPV/Ca(10nm)/Ag, and then the device emitted light through the cathode side Ca/Ag. The polymer emissive layer was DB-PPV (2,3-dibutoxy 1,4-poly(phenylene vinylene)), which was sandwiched between two metal electrodes. One electrode was the bottom reflective anode, which was the surface modified silver film, and the
other one was the top semitransparent double-layer cathode Ca/Ag. Finally, the emitting light emitted from the semitransparent cathode under forward bias. By changing the thickness of
polymer emissive layer in the microcavity structure and the thickness of Ag in the double-layer cathode, narrower EL spectrum and enhancement of emission intensity was obtained simultaneously. By way of appropriately tuned the thickness of polymer emissive layer and
concentration, we general found that the maximum luminance efficiency in the concentration of 0.6% with spin speed of 2000rpm (65nm) and 0.7% with spin speed of 4000rpm (58nm), respectively. This was because most of the recombination or emission zone was closer to the antinode, and the normal direction luminance efficiency increased by a factor of 1.13 ~ 1.65 (2.22 to
3.25cd/A) for 0.6% and 1.01 ~ 1.79 (1.68 to 2.99cd/A) for 0.7%, respectively. Besides, the EL peak wavelength of device with a single emissive layer has a wide variation in the spectral range, from 522 to 622nm, due to the different thickness of DB-PPV. Consequently, tuned the emitting color from original yellowish green (λD=560nm) to saturated green (λD=527nm) and yellow orange (λD=582nm). The full width at half maximum (FWHM) of original EL spectra could be reduced from about 70nm to 20nm.

Contents
Chinese Abstract………………………………………Ⅰ
English Abstract………………………………………Ⅲ
Acknowledgements………………………………………Ⅴ
Contents…………………………………………………Ⅵ
List of Tables…………………………………………Ⅸ
List of Figures………………………………………Ⅹ
Chapter 1 Introduction………………………………1 
 1.1 Introduction………………………………………1
 1.2 Historical development of organic light-emitting diodes (OLEDs) 
   and polymer light-emitting diodes (PLEDs)……………2
 1.3 Advantages of O/PLEDs…………………………4
 1.4 Introductions of top-emitting configuration…5
   1.4.1 Comparisons between top-emission and bottom-emission…………5
   1.4.2 Development of the semitransparent cathode in top-emission………6
   1.4.3 Microcavity O/PLEDs……………………7
 1.5 Motivation……………………………………8
Chapter 2 Basic principle and device operation of PLEDs…………9
 2.1 Introductions of conjugated polymers in organic semiconductors………9
 2.2 Structure of O/PLEDs………………………10
 2.3 Operational mechanism of PLEDs……………………11
 2.4 Theory of fluorescence and phosphorescence………………………12
Chapter 3 The physics of top-emitting PLEDs……………………14
 3.1 Microcavity effects…………………………14
   3.1.1 Introduction…………………………………………14
   3.1.2 Optical characteristics of Fabry-Pérot microcavity……………………15
 3.2 Theoretic aspects on top-emitting devices…………………………………17
   3.2.1 Optical interference effects……………………………………17
   3.2.2 The effect of cavity length on EL peak……………………………………18
   3.2.3 The effect of cavity quality factor on full width at half maximum
         (FWHM) ofthe EL spectrum…………………………19
   3.2.4 The effect of reflectivity on emission intensity………………………20
   3.2.5 The angular dependence of the EL spectrum………………………………21
Chapter 4 Experimental processes and characteristic measurements……………23
 4.1 Experimental processes………………………………23
   4.1.1 Device structures…………………………………………23
   4.1.2 Device fabrication………………………………………26
 4.2 Characteristic Measurements……………………………………29
   4.2.1 Ultraviolet (UV)-vis absorption spectrum and photoluminescence
         (PL) spectrum measurement…………29
   4.2.2 Current-luminance-voltage (I-L-V) measurements…………………………31
   4.2.3 EL spectrum and angular dependence measurements………………………31
Chapter 5 Results and discussions………………32
 5.1 UV-vis absorption and photoluminescence spectra……………………………32
 5.2 The device performances………………………33
   5.2.1 Device performances of bottom-emitting devices…………………………33
   5.2.2 Device performances of top-emitting devices……………………………35
 5.3 Microcavity effects in top-emitting devices……………………………36
   5.3.1 The effect of the thickness of polymer emissive layer on EL peak…36
   5.3.2 Effects of thicknesses of the polymer emissive layer and Ag capping
         layer on device efficiency……………37
   5.3.3 The effect of the thickness of Ag capping layer on EL spectra and
         emission patterns………………………39
   5.3.4 Dependences of EL spectra and emission patterns on viewing angle…………40
Chapter 6 Conclusions and Future work……………42
 6.1 Conclusions………………………………………42
   6.1.1 Enhancement of color purity………………………………42
   6.1.2 Enhancement of device performances………………………43
 6.2 Future work………………………………………44
Reference…………………………………………………45
Table………………………………………………………51
Figure……………………………………………………56
                                    

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校內：2007-07-17公開
校外：2007-07-17公開

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