陽極改質冠醚基接枝聚茀系高分子系元件致高效能高分子發光二極體之研究

Studies on Anode Modification for Polyfluorene Grafted with Crown-Ether Moiety Series Devices to Obtain High Performance in Polymer Light Emitting Diode

薛弘仁(Hong-Ren Syue)

指導教授 ： 陳壽安

國立清華大學/工學院/化學工程學系/碩士(2014年)

摘要

近幾年來白光高分子發光二極體(WPLEDs)引起大家的注意由於它被看好應用於全彩平板顯示器、液晶顯示器的背光源和新世代固態照明光源。相較於白光有機小分子發光二極體(WOLEDs)， 用濕式製程的WPLEDs有降低大面積顯示器製造成本的好處而且也有應用於可撓取基板的潛力。文獻上常用環境敏感金屬如Ba/Ag、Mg：Ag/Ag 、Ca/Ag、Ba/Al、Ca/Al、CsF/Al等當陰極，雖然其具有好的電子注入能力，但它們容易在界面上與氧氣和水氣反應而衰敗，而且這些在金屬-有機界面形成的金屬離子可能會跑進發光層中(EML)影響元件的穩定性。本研究引入polyfluorene grafted with 18-crown-6 ether (PFCn6) chelating to K+取代活性金屬，由於這層水-醇可溶之PFCn6 chelating to K+電子注入層的出現，允許我們只用高功函數的Al當作陰極，其優點為元件對空氣穩定，所以不需要在真空下封裝，進而節省製作成本。
本論文分為兩部份，茲於第四章和第五章分述。在第四章中，我們嘗試了不同的陽極改質方法增加冠醚基接枝聚茀系高分子元件的電洞注入，其中以Chlorinated Indium Tin Oxide(Cl-ITO)為陽極的測試效果最佳。此外，我們報導了一個新的元件結構Cl-ITO/PEDOT，並證明PEDOT的功函數可被Cl-ITO誘導而提升，而且Cl-ITO/PEDOT有界面偶極的效應可增加電洞的注入。在發光層為PSBF元件中的最大亮度可達35812 cd/m2、最大效率可達4.08 cd/A。至於發光層PSBF的EL光譜部份，我們觀察到隨著操作電壓的提高， 在波長500~525 nm的放光變得越來越強，我們認為這現象是電場誘導和PSBF的極性側鏈運動所形成的excimers，整體光色為藍綠光。
在第五章中，我們嘗試了許多的混摻物，其中以螢光的橘黃光小分子Rubrene最適合與PSBF混摻形成高效能的WPLED。在Cl-ITO/PEDOT搭配PFCn6：K+=1：3/Al的PSBF-Rubrene混摻元件中，我們得到白光亮度為61523 cd/m2、最大效率為10.3 cd/A，此亮度表現優於文獻上的WPLED紀錄(~56000 cd/m2)；在Cl-ITO/PEDOT搭配CsF/Al的PSBF-Rubrene混摻元件中，我們得到白光亮度為87615 cd/m2、最大效率為11.1 cd/A，此亮度表現除了優於文獻上的WPLED紀錄(~56000 cd/m2)，而且也可以媲美文獻上使用熱蒸鍍和多調控層的phosphorescent WOLED之記錄(~83000 cd/m2)。到目前為此，我們得到的白光亮度(~87615 cd/m2)是WPLED中最高的。

關鍵字

白光高分子發光二極體 ； 冠醚基接枝聚茀系高分子 ； 氯改質陽極

並列摘要

White polymer light-emitting diodes (WPLEDs) have gained great attention over the last few decades due to their promising applications in full color flat-panel displays, backlighting sources for liquid-crystal displays, and next-generation solid-state lighting sources. In comparison with white organic light-emitting diodes (WOLEDs), WPLEDs fabricated by solution-process have advantages of low-cost manufacture in large-area displays and potential for the use of flexible substrate. In previous literatures, environment-sensitive metals (such as Ba/Ag、Mg：Ag/Ag 、Ca/Ag、Ba/Al、Ca/Al、CsF/Al) were commonly used as cathodes. While they facilitated electron injection, they might undergo degradation by reaction with oxgen and moisture at the interfaces. Also, metal ions formed at the metal-organic interface tended to migrate into the emitting layer (EML) to affect the stability of devices. In this study, we substitute polyfluorene grafted with 18-crown-6 ether (PFCn6) chelating to K+ for environment-sentive metals, due to the presence of electron-injection layer (EIL) of water/methanol-soluble PFCn6 chelating to K+, allowing the use of environment-stable Al as the cathode only. The advantage is that the device is stable to air, and we don't need package in vacuum environment, therefore, saving costs for fabrication.
In this thesis, this contents are divided into two parts giving in chapters 4, 5. In chapter 4, we test many anode modifications in order to increase hole-injection in PFCn6-based devices. Among these modifications, using Chlorinated Indium Tin Oxide(Cl-ITO) is the best solution. Moreover, we demonstrate that the novel device configuration of Cl-ITO/PEDOT is reported for the first time, and we confirm that the raise of work function of PEDOT is induced by Cl-ITO. Also, Cl-ITO/PEDOT has interfacial dipole effect, which can increase hole-injection. The brightness and lumunous efficiency of PSBF-based devices are up to 35812 cd/m2 and 4.08 cd/A, respectively. As for EL spectra of PSBF, the emission at 500~525 nm becomes stronger with gradually increased voltage is observed. We owe this phenomenon to the excimer formation by electric field induction and polar side-chain motion in PSBF. Generally speaking, the whole color is blue-greenish.
In chapter 5, we test many dopant systems in order to find appropriate dye for high performance WPLED. Among these systems, fluorescent orange small molecule Rubrene is the best choice for blending with PSBF. By device combination of Cl-ITO/PEDOT and PFCn6：K+=1：3/Al, the brightness and lumunous efficiency of PSBF-Rubrene-blended devices are up to 61523 cd/m2 and 10.3 cd/A, respectively. In comparison with the record in WPLED literature (~56000 cd/m2), the brightness is much better. By device combination of Cl-ITO/PEDOT and CsF/Al, the brightness and lumunous efficiency PSBF-Rubrene-blended devices are up to 87615 cd/m2 and 11.1 cd/A, respectively. Surprisingly, the brightness is predominately superior to the record in WPLED literature (~56000 cd/m2), and it can compete with the record in phosphorescent WOLED literature by multilayer and vacuum evaporation (~83000 cd/m2). The resulting high white brightness (~87615 cd/m2), to the best of our knowledge, is the highest in WPLED so far.

並列關鍵字

Cl-ITO ； WPLED ； PSBF ； polyfluorene grafted with 18-crown-6 ether (PFCn6) chelating to K+ ； polyspirobifluorene

參考文獻

[1] J. C. W. Chien, “Polyacetylene:Chemistry, Physics, and Material Science”, Academic Press, Orlando (1984).

[5] G. Gustafsson, Y. Cao, G. M. Treacy, F. Klavetter, N. Colaneri, A. J. Heeger, “Flexible light-emitting diodes made from soluble conducting polymer”, Nature, 357 (1992) 477.

[9] C. Kittel, “Introduction to Solid State Physics”, 6th edition, John Wiley & Son, Singapore (1986).

[11] D. A. Skoog, D. M. West, F. J. Holler, “Fundamentals of Analytical Chemistry”, 5th edition, Saunders College Publishing (1988).

[14] A. B. Holmes, D. D. C. Bradley, A. R. Brown, P. L. Burn, J. H. Burroughes, R. H. Friend, N. C. Greenham, R. W. Gymer, D. A. Halliday, R. W. Jackson, A. Kraft, J. H. F. Martens, K .Pichler, I. D. W. Samuel, “Photoluminescence and electroluminescence in conjugated polymeric systems”, Synth. Met., 55-57, (1993), 4031.