臺灣博碩士論文加值系統

在本論文中，將討論金屬電極與有機層間界面的界面電性與特性。由於目前文獻中，對於界面電性與載子在界面的注入過程並不真正地十分確定，所以在部分文獻中的元件模型，在處理載子的注入仍是以傳統的無機半導體為基礎。
當在Al與Alq3間插入一層薄的LiF層，OLED元件的performance有極大的改善，如降低驅動電壓、增加發光效率等。因此首先探討在金屬與有機層間加入一層非常薄的LiF 時，探討LiF對元件性能影響的可能機制。接著，針對關於載子在金屬與有機層間界面處的注入模型做進一步討論。最後，將討論LiF厚度變動時，與注入模型的關係。
關於LiF厚度變動參數對注入模型的影響，在實驗數據中，當LiF為0.5nm時，元件有最佳表現。而當LiF厚度大於0.5nm，元件表現逐漸變差。本論文假設當LiF厚度大於0.5nm時，單純只是由於LiF在此時形成一“完整的絕緣層薄膜”降低了載子的注入而使元件表現變差。而在推導過程中，假設與金屬功函數參數無關；且由於有機材料的分子結構與無機半導體的共價鍵晶格結構不同，因此假設平衡時在界面處無類似無機半導體p-n junction的能帶彎曲現象。最後得到的結果，與文獻所示相吻合。
因此經由本文理論推導與傳輸模型的模擬結果，證明載子的注入與金屬的功函數幾乎無關，而是由金屬與有機層間所形成的界面型態所決定。再者，對Al/LiF/Alq3架構，LiF在0.5nm時，其界面處的反應達到飽和；所以當LiF厚度大於0.5nm時，LiF在此時形成一“完整的絕緣層薄膜”，因此當LiF厚度大於0.5nm時，元件表現變差，其主要的原因是由於載子通過時，受到絕緣層的阻礙。

In this dissertation, the electrical characteristics of the interface between the metal cathode and organic layer in OLEDs are detailed investigated. Currently, surveying on the literature, it is limited in understanding the interfacial characteristics and the injection process of electron at interface, therefore the carrier injection phenomena investigated here is still based on the traditionally inorganic semiconductor physics.
As a thin LiF layer inserted between the Al and Alq3 layers, the performance of OLED shown a great deal of improvement, such as lowering the driving voltage and increasing the luminescence efficiency. At first, we study how a very thin LiF layer affecting the performance of OLED device, and the feasible mechanisms attributed to this improvements. Then, the further discussion should be focused on the injection model built for the charge at metal/organic interfaces. Finally, the relationship that the injection model related to the variety of LiF layer thickness could be investigated.
From the experimental data, the Al/LiF/Alq3 devices with the LiF thickness of 0.5nm have shown the best performance, and the device performance decay as the thickness of LiF layer increased over 0.5nm. In this study, it assumes that the LiF layer just forms an “integrated” thin insulating film and lowing the charge injection as the layer thickness over 0.5nm, and it also assume that in model derived process is independent on the metal work function.
Since the molecular structure of organic materials is quite difference from the valence band structure in inorganic semiconductor materials, it could be assumed no band bending like that the p-n junction at the interface of inorganic semiconductor under thermal equilibrium. After theoretical approach, we get the reasonable results by comparing with the literatures reported recently.
The conclusion of this study reveals that the charge injection is independent on the metal work function, but is determined by the interface structure characteristic of interface structure at metal/organic interfaces. Furthermore, in the Al/LiF/Alq3 structure, the chemical reaction is saturated at the interface as the LiF layer forms a “integrated” thin insulating film. Therefore, the device performance decay is the effect due to the insulating LiF layer when the thickness of LiF layer is over 0.5nm.

第一章緒論...........................................1
第一節有機發光二極體的介紹..................1
1.1.1 OLED與平面顯示器簡介.....................1
1.1.2 OLED的發展概況...........................2
1.1.3 小分子與高分子OLED的比較.................3
第二節有機發光二極體的工作原理..............5
1.2.1 螢光與磷光...............................5
1.2.2 有機電致發光與染料的摻雜.................5
1.2.3 OLED元件架構.............................6
1.2.4 多彩、全彩OLED元件架構...................8
第三節論文目的與章節簡介....................9
第二章文獻討論......................................10
第一節陰極電極的演進.......................10
第二節陰極/有機層間的界面電性特性..........12
第三節陰極/有機層間注入模型的討論...........17
2-3-1 空間電荷限制與注入限制傳輸...............17
2-3-2 界面傳輸模型(一).........................20
2-3-3 界面傳輸模型(二).........................26
第三章模型推導與討論.................................29
第一節條件..................................29
第二節考慮MIS穿透二極體的模型，與方形能障的穿透率....31
第三節考慮載子的分佈.........................33
第四節討論...................................35
第四章結論............................................39
Reference................................................40
圖表.....................................................46

[1] C. W. Tang, S. A. VanSlyke, C. H. Chen, “Electroluminescence of doped organic thin films” J. Appl. Phys., 65, 361, 1989[2] C.W. Tang and S.A. VanSlyke, “Organic electroluminescent diodes”, Appl. Phys. Lett., Vol. 51, p 913, 1987[3] C. Adachi, S. Tokito, T. Tsutsui,S. Saito, Jpn. J. Appl. Phys., 27, L713., 1988[4] M. Era, C. Adachi, T. Tsutsui, S. Saito, Chem. Phys. Lett., 178, 488., 1991[5] J. Kido, M. Kohda, K. Okuyama, K. Nagai, “Organic electroluminescent devices based on molecularly doped polymers”, Appl. Phys. Lett.,61,761,1992[6] J. Kalinowski, P. Di Marco, M. Cocchi, V. Fattori, N. Camaioni, J. Duff, “Voltage-tunable-color multilayer organic light emitting diode” Appl. Phys. Lett.,Vol. 68, p2317, 1996[7] P. E. Burrows, S. R. Forrest, “Color-Tunable Organic Light Emitting Devices”1997[8] [液晶平面顯示器:技術專文] 呂伯彥, “有機光電半導體材料之應用”, 2001[9] C. C. Wu, J. C. Sturm, R. A. Register, M. E. Thompson, “Integrated three-color organic light-emitting devices”, A.P.L., Vol. 69, p3117, 1996[10] G. Gu, G. Parthasarathy, and S. R. Forrest, “A metal-free, full-color stacked organic light-emitting device” A.P.L., Vol. 74, p305, 1999[11] L. S. Hung, C. W. Tang, and M. G. Mason, “Enhanced electron injection in organic electroluminescence devices using an Al/LiF electrode” A. P. L., Vol. 70, p152, 1997[12] V. Choong, Y. Park, Y. Gao, T. Wehrmeister, K. Mu¨llen, B. R. Hsieh, and C. W. Tang, “Dramatic photoluminescence quenching of phenylene vinylene oligomer thin films upon submonolayer Ca deposition”, Appl. Phys. Lett., Vol. 69, p 1492, 1996[13] V.-E. Choong, Y. Park, Y. Gao, T. Wehrmeister and K. Mullen, B. R. Hsieh, C. W. Tang, “Effects of Al, Ag and Ca on luminesecnce of organic materials”, J. Vac. Sci. Technol. A, Vol. 15, p1745, 1997[14] T. Wakimoto, S. Kawami, K. Nagayama, Y. Yonemoto, R. Murayama, J. Funaki, H. Sato, H. Nakada, and K. Imai, International Symposium on Inorganic and Organic Electroluminescence, Hamamatsu, p 77,1994[15] T. Wakimoto, Y. Fukuda, K. Nagayama, A.YoKoi, H.Nakada, M. Tsuchida, ”Organic EL Cells Using Alkaline Metal Compounds as Electron Injection Materials”, IEEE transactions on electron devices, Vol. 44, p 1245, 1997[16] L. S. Hung, C. W. Tang, and M. G. Mason, “Enhanced electron injection in organic electroluminescence devices using an Al/LiF electrode” A. P. L., Vol. 70, p152, 1997[17] F. Li and H. Tang, J. Anderegg, J. Shinara, “Fabrication and electroluminescence of double-layered organic light-emitting diodes with the Al2O3 /Al cathode” A. P. L., Vol. 70, p1233, 1997[18] Y. Parka and J. Lee, S. K. Lee, D. Y. Kim, “Photoelectron spectroscopy study of the electronic structures of Al/MgF2/tris-(8-hydroxyquinoline) aluminum interfaces” A. P. L., Vol. 79, p105, 2001[19] E. I. Haskal, A. Curioni, P. F. Seidler, and W. Andreoni, “Lithium-aluminum contacts for organic light-emitting devices” A. P. L., Vol. 71, p1151, 1997[20] M. B. Huang, K. McDonald, J. C. Keay, Y. Q. Wang, S. J. Rosenthal, R. A. Weller, L. C. Feldman, “Suppression of penetration of aluminum into 8-hydroxyquinoline aluminum via a thin oxide barrier” A. P. L., Vol. 73, p2914, 1998[21] Asuka Yamamori, Sachiko Hayashi, Toshiki Koyama, and Yoshio Taniguchi, “Transparent organic light-emitting diodes using metal acethylacetonate complexes as an electron injective buffer layer”, Applied Physics Letters, Vol. 78, p3343, 2001[22] Walter Rieß, Heike Riel, Paul F. Seidler, Horst Vestweber, “Organic-inorganic multilayer structures: a novel route to highly efficient” synthetic metals, Vol. 99, p 213, 1999[23] Kazuhiko Sekia, Naoki Hayashib, Hiroshi Ojib, Eisuke Itoc, Yukio Ouchib, Hisao Ishiib, “Electronic structure of organic/metal interfaces” thin solid films, Vol. 393, p298, 2001[24] I. G. Hill, A. J. Makinen, and Z. H. Kafafib, “Distinguishing between interface dipoles and band bending at metal/tris-(8-hydroxyquinoline) aluminum interfaces” A. P. L., Vol. 77, p1825, 2000[25] G. E. Jabbour, Y. Kawabe, S. E. Shaheen, J. F. Wang, M. M. Morrell, B. Kippelen, and N. Peyghambarian, “Highly efficient and bright organic electroluminescent devices with an aluminum cathode” A. P. L., Vol. 71, p1762, 1997[26] H. Heil, J. Steiger, S. Karg, M. Gastel, H. Ortner, and H. von Seggern, M. Stoßel, “Mechanisms of injection enhancement in organic light-emitting diodes through an Al/LiF electrode” A. P. L., Vol. 89, p420, 2001[27] M. Probst and R. Haight, “Diffusion of metals into organic films” A. P. L., Vol. 70, p1420, 1997[28] A. Rajagopal and A. Kahn, “Photoemission spectroscopy investigation of magnesium—Alq3 interfaces” J. A. P., Vol. 84, p355, 1998[29] S. T. Lee, Z. Q. Gao, L. S. Hung, “Metal diffusion from electrodes in organic light-emitting diodes” A. P. L., Vol. 75, p1404, 1999[30] M. Stoßel, J. Staudigel, F. Steuber, J. Blassing, J. Simmerer, A. Winnacker, H. Neuner, D. Metzdorf, H. —H. Johannes, W. Kowalsky, “Electron injection and transport in 8-hydroxyquinoline aluminum” synthetic metals, Vol. 111-112, p19, 2000[31] S. T. Lee, X. Y. Hou, M. G. Mason, C. W. Tang, “Energy level alignment at Alq/metal interfaces” A. P. L., Vol. 72, p1593, 1998[32] I. G. Hill, A. J. Makinen, and Z. H. Kafafi, “Initial stages of metal organic semiconductor interface formation” J. A. P., Vol. 88, p889, 2000[33] M. A. Baldo and S. R. Forrest, “Interface-limited injection in amorphous organic semiconductors” Physical Review B, Vol 64, p85201, 2001[34] Y. Park, V.-E. Choong, B. R. Hsieh, C. W. Tang, and Y. Gao, “Gap-State Induced Photoluminescence Quenching of Phenylene Vinylene Oligomer and Its Recovery by Oxidation” Physical Review Letters, Vol. 78, p3955, 1997[35] Quoc Toan Le, Li Yan, Yongli Gao, M. G. Mason, D. J. Giesen, and C. W. Tang, “Photoemission study of aluminum/tris-(8-hydroxyquinoline) aluminum and aluminum/LiF/tris-(8-hydroxyquinoline) aluminum interfaces” J. A. P., Vol. 87, p375, 2000[36] K.L. Wanga, B. Laia, M. Lua, X. Zhoua, L.S. Liaoa, X.M. Dinga, X.Y. Houa, S.T. Lee, “Electronic structure and energy level alignment of Alq3/Al2O3/Al and Alq3/Al interfaces studied by ultraviolet photoemission spectroscopy” thin solid films, Vol. 363, p178, 2000[37] Junji Kido, Toshio Matsumoto, “Bright organic electroluminescent devices having a metal-doped electron-injecting layer” A. P. L., Vol. 73, p2866, 1998[38] V.-E. Choong, M. G. Mason, C. W. Tang, Yongli Gao, “Investigation of the interface formation between calcium and tris-(8-hydroxy quinoline) aluminum” A. P. L., Vol. 72, p2689, 1998[39] P. E. Burrows, Z. Shen, V. Bulovic, D. M. McCarty, S. R. Forrest, J. A. Cronin and M. E. Thompson, “Relationship between electroluminescence and current transport in organic heterojunction light-emitting devices” J. A. P., Vol. 79, p7991, 1996[40] W. Brutting, S. Berleb, A.G. Muckl, “Space-charge limited conduction with a field and temperature dependent mobility in Alq light-emitting devices” Synthetic metals, Vol. 122, p99, 2001[41] I. D. Parker, “Carrier tunneling and device characteristics in polymer light-emitting diodes” J. A. P., Vol. 75, p1656, 1994[42] J. C. Scott, G. G. Malliaras, “Charge injection and recombination at the metal-organic interface” Chemical Physics Letters, Vol. 299, p115, 1999[43] H. Young, “Dipolar lattice model of disorder in random media Analytical evaluation of the Gaussian disorder model” Philos. Mag., Vol. 72, p435, 1995[44] L. Martin, J. D. Kress, I. H. Campbell, and D. L. Smith, “Dipolar lattice model of disorder in random media Analytical evaluation of the Gaussian disorder model” Phys. Rev. B, Vol. 61, p15804, 2000[45] E. Tutis, M. N. Bussac, B. Masenelli, M. Carrard, L. Zuppiroli, “Numerical model for organic light-emitting diodes” J. A. P., Vol. 88, p889, 2000[46] T. Mori, H. Fujikawa, S. Tokito, Y. Taga, “Electronic structure of 8-hydroxyquinoline aluminum/LiF/Al interface for organic electroluminescent device studied by ultraviolet photoelectron spectroscopy” A. P. L., Vol. 73, p2763, 1998[47] G. Parthasarathy, C. Shen, A. Kahn, and S. R. Forrest, “ Lithium doping of semiconducting organic charge transport materials” A. P. L., Vol. 89, p4986, 2001[48] S. M. Sze, “Physics of Semiconductor Device” 2nd Edition, Chapter 9[49] S. M. Sze, “Physics of Semiconductor Device” 2nd Edition, Chapter 8[50] S. Y. Park, C. H. Lee, W. J. Song, C. Seoul, “ Enhanced electron injection in organic light-emitting devices using Al/LiF electrodes” Current Applied Physics, Vol. 1, p116, 2001[51] B. Massenelli, D. Berner, M. N. Bussac. F. Nuesch, L. Zuppiroli, “ Simulation of charge injection enhancements in organic light-emitting diodes” A. P. L., Vol. 79, p4438, 2001[52] H. Fujikawa, T. Mori, K. Noda, M. Ishii, S. Tokito, Y. Taga, “Organic electroluminescent devices using alkaline-earth fluorides as an electron injection layer” Journal of luminescence, Vol. 87-89, p1177, 2000