臺灣博碩士論文加值系統

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

1. M. Pope, H. Kallmann, and P. Magnante, “Electroluminescence in Organic
Crystals”, J. Chem. Phys. 38 (8), pp. 2042-2043 (1963)
2. W. Helfrich and W. G. Schneider, “Recombination Radiation in
Anthracene Crystals”, Phys. Rev. Lett. 14 (7), pp. 229-231 (1965)
3. C. W. Tang and S. A. VanSlyke, “Organic electroluminescent diodes”,
Appl. Phys. Lett. 51 (12), pp. 913-915 (1987)
4. J. H. Burroughes, D. D. C. Bradley, A. R. Brown, R. N. Marks, K. Mackay,
R. H. Friend, P. L. Burns, and A. B. Holmes, “Light emitting diodes based
on conjugated polymers”, NATURE 347 (11), pp. 539-541 (1990)
5. D. Braun and A. J. Heeger, “Visible light emission from semiconducting
polymer diodes”, Appl. Phys. Lett. 58 (18), pp. 1982-1984 (1991)
6. S. Kho, S. Sohn and D. Jung, “Effects of N2 Plasma Treatment of the Al
Bottom Cathode on the Characteristics of Top-Emission-Inverted Organic-
Light-Emitting Diodes”, Jpn. J. Appl. Phys. 42, pp. L552-L555 (2003)
7. M.-H. Lu, M. S. Weaver, T. X. Zhou, M. Rothman, R. C. Kwong, M. Hack,
and J. J. Brown, “High-efficiency top-emitting organic light-emitting
devices”, Appl. Phys. Lett. 81 (21), pp. 3921-3923 (2002)
8. G. Gu, V. Bulovic, P. E. Burrows, S. R. Forrest, and M. E. Thompson,
“Transparent organic light emitting devices”, Appl. Phys. Lett. 68 (19),
pp. 2606-2608 (1996)
9. G. Parthasarathy, P. E. Burrows, V. Khalfin, V. G. Kozlov, and S. R. Forrest,
“A metal-free cathode for organic semiconductor devices”, Appl. Phys. Lett.
72 (17), pp. 2138-2140 (1998)
10. L. S. Hung, C. W. Tang, M. G. Mason, P. Raychaudhuri, and J. Madathil,
“Application of an ultrathin LiF/Al bilayer in organic surface-emitting
diodes”, Appl. Phys. Lett. 78 (4), pp. 544-546 (2001)
11. S. Han, X. Feng, Z. H. Lu, D. Johnson, and R. Wood, “Transparent
cathode for top-emission organic light-emitting diodes”, Appl. Phys. Lett.
82 (16), pp. 2715-2717 (2003)
12. H. Riel, S. Karg, T.Beierlein, B.Rubstaller, and W. Rieβ, “Phosphorescent
top-emitting organic light-emitting devices with improved light
outcoupling”, Appl. Phys. Lett. 82 (3), pp. 466-468 (2003)
13. R. B. Pode, C. J. Lee, D. G. Moon, and J. I. Han, “Transparent conducting
metal electrode for top emission organic light-emitting devices: Ca–Ag
double layer”, Appl. Phys. Lett. 84 (23), pp. 4614-4616 (2004)
14. C.-C. Wu, C.-W. Chen, C.-L. Lin, and C.-J. Yang, “Advanced Organic Light-
Emitting Devices for Enhancing Display Performances”, J. Display Tech. 1
(2), pp. 248-266 (2005)
15. F. Rahman, N. P. Johnson, and T. Slight, “Electrical conduction in light-
emitting organic polymer Schottky diodes”, J. Appl. Phys. 98, 124504
(2005)
16. M. A. Baldo, S. Lamansky, P. E. Burrows, M. E. Thompson, and S. R.
Forrest,“Very high-efficiency green organic light-emitting devices based
on electrophosphorescence”, Appl. Phys. Lett. 75 (1), pp. 4-6 (1999)
17. L. Yang, M. C. Wu, K. Tai, T. T.-Ek, and R. A. Logan, “InGaAsP(1.3
μm)/InP vertical-cavity surface-emitting laser grown by metalorganic
vapor phase epitaxy”, Appl. Phys. Lett. 56 (10), pp. 889-891 (1990)
18. E. F. Schubert, Y.-H. Wang, A. Y. Cho, L.-W. Tu, and G. J. Zydzik,
“ Resonant cavity light-emitting diode”, Appl. Phys. Lett. 60 (8),
pp.921-923 (1992)
19. U. Lemmer, R. Hennig, W. Guss, A. Ochse, J. Pommerehne, R. Sander, A.
Greiner, R. F. Mahrt, H. Bässler, J. Feldmann, and E. O. Göbel,
“Microcavity effects in a spin-coated polymer two-layer system”, Appl.
Phys. Lett. 66 (11), pp. 1301-1303 (1995)
20. S. Dirr, S. Wiese, H.-H. Johannes, and W. Kowalsky, “Organic Electroand
Photoluminescent Microcavity Devices”, Adv. Mater. 10 (2), pp. 167-171
(1998)
21. E. F. Schubert, N. E. J. Hunt, R. J. Malik, M. Micovic, and D. L. Cliller,
“Temperature and Modulatilon Characteristics of Resonant-Cavity Light-
Emitting Diodes”, J. Lightwave Tech. 14 (7), pp. 1721-1729 (1996)
22. E. F. Schubert, N. E. J. Hunt, M. Micovic, R. J. Malik, D.L. Sivco, A. Y.
Cho, and G. J. Zydzik, “Highly Efficient Light-Emitting Diodes with
Microcavitys”, SCIENCE. 265, pp.943-945 (1994)
23. H. Riel, S. Karg, T. Beierlein,W. Ries, and K. Neyts, “Tuning the
emission characteristics of top-emitting organic light-emitting devices by
means of a dielectric capping layer: an experimental and theoretical
study,” J. Appl. Phys. 94 (8), pp. 5290–5296 (2003)
24. F. Jean, J.-Y. Mulot, B. Geffroy, C. Denis, and P. Cambon, “Microcavity
organic light-emitting diodes on silicon”, Appl. Phys. Lett. 81 (9), pp.
1717-1719 (2002)
25. S.-F. Hsu, C.-C. Lee, S.-W. Hwang, and C.-H. Chen, “Highly efficient top-
emitting white organic electroluminescent devices”, Appl. Phys. Lett. 86,
253508 (2005)
26. A. Dodabalapur, L. J. Rothberg, T. M. Miller, and E. W. Kwock,“Microcavity
effects in organic semiconductors”, Appl. Phys. Lett. 64 (19), pp. 2486-
2488 (1994)
27. S. F. Hsu, C.-C. Lee, A. T. Hu, and C. H. Chen, “Fabrication of blue
top-emitting organic light-emitting devices with highly saturated color”,
Current Applide Physics 4, pp. 663-666 (2004)
28. X. T. Hao, F. R. Zhu, K. S. Ong, and L. W. Tan, “Colour tunability of
polymeric light-emitting diodes with top emission architecture”,
SEMICONDUCTOR SCIENCE AND TECHNOLOGY, 21 (1), pp. 19-24 (2006)
29. H. Peng, J. Sun, X. Zhu, X. Yu, M. Wong, and H.-S. Kwok, “High-efficiency
microcavity top-emitting organic light-emitting diodes using silver
anode”, Appl. Phys. Lett. 88, 073517 (2006)
30. E. F. Schubert, A. M. Vredenberg, N. E. J. Hunt, Y. H. Wong, P. C. Becker,
J. M. Poate, D. C. Jacobson, L. C. Feldman, and G. J. Zydzik, “Giant
enhancement of luminescence intensity in Er-doped Si/SiO2 resonant
cavities”, Appl. Phys. Lett. 61 (12), pp. 1381-1383 (1992)
31. H. Becker, S. E. Burns, N. Tessler, and R. H. Friend, “Role of optical
properties of metallic mirrors in microcavity structures”, J. Appl. Phys.
81 (6), pp. 2825-2829 (1997)
32. Y.-K. Su and W.-C. Lu, “Effects of different thermal annealing on the
performance of DB-PPV based PLED”, Thesis for Master of Science degrees
in National Cheng Kung University, Taiwan, R. O. C. (2005)
33. C. W. Chen, P. Y. Hsieh, H. H. Chiang, C. L. Lin, H. M. Wu, and C. C. Wu,
“Top-emitting organic light-emitting devices using surface-modified Ag
anode”, Appl. Phys. Lett. 83 (25), pp. 5127-5129 (2003)
34. H. W. Choi, S. Y. Kim, K.-B. Kim, Y.-H. Tak, and J.-L. Lee, “Enhancement
of hole injection using O2 plasma-treated Ag anode for top-emitting
organic light-emitting diodes”, Appl. Phys. Lett. 86, 012104 (2005)
35. C.J. Lee, R.B. Pode, D.G. Moon and J.I. Han, “Realization of an efficient
top emission organic light-emitting device with novel electrodes”, Thin
Solid Film, 467, pp. 201-208 (2004)
36. T.-W. Lee and O O. Park, “The Effect of Different Heat Treatments on the
Luminescence Efficiency of Polymer Light-Emitting Diodes”, Adv. Mater. 12
(1), pp. 801-804 (2000)
37. J. Liu, Y. Shi, L. Ma, and Y. Yang, “Device performance and polymer
morphology in polymer light emitting diodes: The control of device
electrical properties and metal-polymer contact”, J. Appl. Phys. 88 (2),
pp. 605-609 (2000)
38. S. Sinha and A. P. Monkman, “Effect of electric field, solvent, and
concentration on the electroluminescence spectra and performance of
poly[2-methoxy-5-(2-ethyl-hexyloxy)-1,4-phenylene vinylene] based light
emitting diodes”, J. Appl. Phys. 93 (9), pp. 5691-5700 (2003)
39. Y. Shi, J. Liu, L. Ma, and Y. Yang, “Device performance and polymer
morphology in polymer light emitting diodes: The control of thin film
morphology and device quantum efficiency”, J. Appl. Phys. 87 (9), pp.
4254-4263 (2000)
40. S. Tokito, K. Noda, and Y. Taga, “Strongly directed single mode emission
from organic electroluminescent diode with a microcavity”, Appl. Phys.
Lett. 68 (19), pp.2633-2635 (2005)
41. L. Hou, Q. Hou, Y. Mo, J. Peng, and Y. Cao, “All-organic flexible polymer
microcavity light-emitting diodes using 3M reflective multilayer polymer
mirrors”, Appl. Phys. Lett. 87, 243504 (2005)