濕式製程有機發光二極體製作與色度特性之研究

Investigation of Fabrication and Chromaticity Characteristics of Solution-Processed Organic Light Emitting Diodes

范嘉展(Chia-Chan Fan)

指導教授 ： 林皓武

國立清華大學/工學院/材料科學工程學系/碩士(2013年)

摘要

本篇論文研究濕式製程有機發光二極體的色度、元件結構與效率表現之關係，透過色彩模擬、元件結構優化以及新穎製程實現高效率單色光與白光有機發光二極體元件。
首先，在本篇論文序論的部分，先對有機電致發光二極體的發展歷史做回顧並簡述有機發光二極體於顯示器與固態照明的應用，接下來對其發光原理、量測技術、製程方式以及白光有機發光二極體作有系統的介紹。
論文的第二部分，我們導入頻譜線性疊加的概念，模擬多元白光頻譜並於Commission International de l’Eclairage (CIE)色座標中對黑體輻射曲線作逼近，設計出高color rendering index (CRI)與高色度之白光頻譜。利用上述模擬頻譜調整客體發光材料間的摻雜比例於單一發光層中，以刮刀製程製作雙元、三元與四元單發光層濕式製程白光元件並驗證數值模擬的結果。其中，雙元高色溫白光元件，發光色溫為5700 K，CRI值為59，而四元暖白光元件，放光色溫為2700 K，CRI高達85，並具備高白光色純度(Du’v’ = +0.0009)。此外透過線性疊加模擬結果，優化出PL頻譜波峰為555 nm的Os基團的黃光磷光材料之最佳元件表現，所製作出之三元白光刮刀元件，其CRI可達84，色溫為2845 K。
論文第三部分，我們摻雜電洞傳輸材料4,4′-Cyclohexylidenebis[N,N-bis- (4-methylphenyl)benzenamine] (TAPC)與電子傳輸材料或雙極性傳導特性材料作為共主體材料，並以最佳條件製作四元共摻雜白光有機發光二極體元件。此外，我們分別透過兩種方式增加元件效率，第一在元件外部添加具微米透鏡之光學膜層以及透明半球之光學構造增加外部出光量，分別使元件之外部量子效率(external quantum efficiency, EQE)提升1.3倍與1.89倍；第二，我們於元件內部優化膜層厚度與調變電洞注入層致使白光元件在沒有外部增益層的情況下，效率達44.6 cd/A、35.6 lm/W、EQE = 21.9%。

關鍵字

有機發光二極體 ； 濕式製程 ； 色度

並列摘要

In this thesis, we focus on chromaticity modeling, device optimization and innovative fabrication process of solution-processed organic light emitting diodes (OLEDs).
First, in the introduction, we briefly review the history and development of organic electroluminescence devices, and the application of OLEDs in displays and solid state lighting. Operating princioples, measurement method, and device fabrication of OLEDs, and in particular, white light emitting devices are also discussed.
In the second part of the thesis, chromaticity simulation of white OLEDs by superposition of individual illuminators is introduced. Design rules of approaching Planckian locus in Commission International de l’Eclairage (CIE) coordinates diagram are porposed. A series of high color rendering index (CRI) and high chromaticity white OLED spectrum have been calculated. By adjusting the emitters doping concentrations in single emissive layer, binary, ternary, and quaternary dopants blade-coated white OLEDs were fabricated to verify the numerical models. The binary white OLED exhibited high correlated color temperature (CCT) of 5700 K with CRI value of 59, while the quaternary white OLED exhibited a higher CRI value of 85 and a warm white illumiation of CCT = 2700 K. Furthermore, according to the model, the devices with a novel Os(II)-based emitter (emission λmax = 555 nm) were designed and fabricated. The ternary white OLED utilizing this novel Os(II) emitter delivered a high CRI value of 84 at CCT = 2845 K and small deviation to Plancknain locus (Du’v’ = +0.0009).
In the third part, co-host system for solution processed emissive layer has been investigated. High hole-mobility material 4,4′-Cyclohexylidenebis[N,N-bis(4- methylphenyl)benzenamine] (TAPC) was blended with either electron transporting materals or bi-polar hosts. By tuning the ratio of hosts and optimizing the device strcture, highly efficient solution-processed co-host white OLEDs devices were fabricated. Furthermore, we separately explored two different methods to increase the external quantum efficiency (EQE) of the white OLEDs. Exteriorly, by utilizing micro-lens film and hemisphere structure, the light out-coupling efficiencies were enhanced by 1.3 times and 1.89 times, respetively. Interiorly, by fine-tuning the thickness of the emissive layer and carefully selecting the hole injection materials, a highly efficient solution-processed white OLED with current efficiency (CE) of 44.6 cd/A, power efficacy (PE) of 35.6 lm/W, and EQE up to 22.9 % was obtained without out-coupling enhancement structures.
In the fourth part, we have analyzed the optoelectronic properties of crosslinkable hole transporting materials. Monochromatic multiple-layer solution-processed OLEDs were fabricated. The green OLED exhibited CE of 56.8 cd/A, PE as high as 54.6 lm/W, and EQE up to 15.9 %.
In the last part of the thesis, we present the preliminary results of quantum dot light emitting diodes utilizing organic transporting layers and zinc oxide nanoparticles.

並列關鍵字

Organic Light Emitting Diodes ； Solution Process ； Chromaticity

參考文獻

22. (a) Lee, T.-W.; Noh, T.; Choi, B.-K.; Kim, M.-S.; Shin, D. W.; Kido, J., High-efficiency stacked white organic light-emitting diodes. Appl. Phys. Lett. 2008, 92 (4), 043301; (b) Chang, C.-C.; Chen, J.-F.; Hwang, S.-W.; Chen, C. H., Highly efficient white organic electroluminescent devices based on tandem architecture. Appl. Phys. Lett. 2005, 87 (25), 253501; (c) Kim, H.-K.; Kim, D. G.; Lee, K. S.; Huh, M. S.; Jeong, S. H.; Kim, K. I.; Seong, T.-Y., Plasma damage-free sputtering of indium tin oxide cathode layers for top-emitting organic light-emitting diodes. Appl. Phys. Lett. 2005, 86 (18), 183503; (d) Kanno, H.; Holmes, R. J.; Sun, Y.; Kena-Cohen, S.; Forrest, S. R., White Stacked Electrophosphorescent Organic Light-Emitting Devices Employing MoO3 as a Charge-Generation Layer. Adv. Mater. 2006, 18 (3), 339; (e) Park, J. S.; Lee, B. R.; Lee, J. M.; Kim, J.-S.; Kim, S. O.; Song, M. H., Efficient hybrid organic-inorganic light emitting diodes with self-assembled dipole molecule deposited metal oxides. Appl. Phys. Lett. 2010, 96 (24), 243306.

27. (a) Yang, X.; Müller, D. C.; Neher, D.; Meerholz, K., Highly Efficient Polymeric Electrophosphorescent Diodes. Adv. Mater. 2006, 18 (7), 948-954; (b) Wu, H. B.; Zou, J. H.; Liu, F.; Wang, L.; Mikhailovsky, A.; Bazan, G. C.; Yang, W.; Cao, Y., Efficient Single Active Layer Electrophosphorescent White Polymer Light-Emitting Diodes. Adv. Mater. 2008, 20 (4), 696; (c) Nakamura, A.; Tada, T.; Mizukami, M.; Yagyu, S., Efficient electrophosphorescent polymer light-emitting devices using a Cs/Al cathode. Appl. Phys. Lett. 2004, 84 (1), 130.

6. Pope, M.; Kallmann, H. P.; Magnante, P., Electroluminescence in Organic Crystals. J. Chem. Phys 1963, 38 (8), 2042.

7. Vincett, P. S.; Barlow, W. A.; Hann, R. A.; Roberts, G. G., Electrical conduction and low voltage blue electroluminescence in vacuum-deposited organic films. Thin Solid Films 1982, 94 (2), 171.

8. Tang, C. W.; VanSlyke, S. A., Organic electroluminescent diodes. Appl. Phys. Lett. 1987, 51 (12), 913.