混合式雙主發光體磷光有機發光二極體之研究

The Study of Hybrid Double Host Phosphorescent Organic Light Emitting Diodes

洪鄰安(Lin-Ann Hong)

指導教授 ： 莊賦祥 ； 蔡裕勝

國立虎尾科技大學/電機資訊學院/光電與材料科技研究所/博士(2015年)

摘要

本研究本研究主體分為三大項，第一項是磷光系統製作藍色與白色有機發光二極體；第二項螢磷混合系統製作白色有機發光二極體
首先第一項磷光系統研究主題分為三大類，主題一研究雙層主發光體結構，利用兩種不同載子傳輸特性及能階差異的主發光體搭配藍色磷光摻雜物(FIrpic)製作藍色磷光有機發光二極體，由於雙層發光層結構其電洞電子複合區域會隨這工作電壓的改變產生遷移，造成白光元件會產生色偏的情形，因此本研究將利用捕捉電洞特性的紅色摻雜物材料(Os)在兩發光層接面處，可有效降低色偏的產生，以得到高效率白色磷光有機發光二極體。主發光體結構利用具電洞傳輸特性TCTA及雙極性傳輸特性26DCzPPY做為雙發光層的主發光體材料，藉由不同載子傳輸特性及能階的差異，使電洞電子在發光層內再結合機率提升，以提高元件發光效率。藍色磷光有機發光二極體在亮度為1000 cd/m2時，電流效率為35.1 cd/A，功率效率為25.6 lm/W及CIE座標為(0.144, 0.328)；再將捕捉電洞特性的紅色磷光摻雜物(Os)摻雜於於TCTA與26DCzPPY接面處，利用Os具有電洞捕捉的功能，使電洞可有效捕捉在其介面處，進而避免白色磷光元件隨電壓改變而發生的色偏的現象。在亮度為1000 cd/m2時，電流效率為34.4 cd/A，功率效率為22.0 lm/W及CIE座標從4至10 V偏移為"∆" x=+0.005，"∆" y=+0.004。
主題二研究單層混合式主發光體結構，研究降低電洞電子注入至發光層能階能障的影響，以提升元件載子注入效應，藉以得到較佳的再結合機率，提高藍色磷光元件發光效率。研究中利用單極性電洞傳輸特性材料(TCTA)與電子傳輸特性材料(3TPYMB)，以共摻雜1:1方式製作混合式雙極性主發光體結構。電流效率為36.0 cd/A，功率效率為27.5 lm/W。而紅色磷光摻雜材料Os則摻雜於單層混合式雙極性主發光層中間處，以得到高效率白色磷光有機發光二極體。電流效率為36.1 cd/A，功率效率為26.4 lm/W及CIE座標從4至10 V偏移為"∆" x=+0.019，"∆" y=+0.005。
主題三結合上述兩主題所提到的雙主發光體結構與單層混合式結構製作雙層混合式主發光體結構，研究中使用雙極性材料26DczPPy搭配具電洞傳輸特性材料TCTA與電子傳輸特性材料PPT透過共摻雜(1:1)方式製作雙層混合式主發光體結構，以提升電荷載子注入至主發光層，提升藍色磷光元件發光效率。其元件發光亮度為1000 cd/m2，操作電壓為4.4 V，電流密度為2.4 mA/cm2，電流效率為41.7 cd/A，功率效率為30 lm/W。紅色磷光摻雜物Os摻雜發光層中間，以製作高效率白色磷光元件。在元件發光亮度為1000 cd/m2下，操作電壓為4.6 V，電流密度為2.9 mA/cm2，電流效率34.0 cd/A，功率效率可達23.6 lm/W，在操作電壓從4至10 V，其CIE色座標由(0.311,0.357)偏移至(0.307,0.358) ("∆" x=-0.004，"∆" y=+0.001)。若再搭配BEF，元件電流效率可再提升至42.5 cd/A，功率效率達到29.5 lm/W。
第二項研究主題為螢磷混合式白光有機發光二極體，利用雙極性螢光主發光體材料BH-05搭配藍色螢光摻雜物EB-502作為藍光發光層及雙極性之磷光主發光體材料EPH-31摻雜Os作為紅色磷光發光層，並且將兩種系統間加入間隔層，能有效抑制能量的損失。其間隔層於兩發光層之間厚度為4 nm分別為BH-05 (2 nm)/EPH-31 (2 nm)及磷光發光層與電子傳輸層之間2 nm為EPH-31 (2 nm)，其發光亮度在1000 cd/m2時，操作電壓為4.5 V，電流密度微5.9 mA/cm2，電流效率17.5 cd/A，功率效率為12.5 lm/W及CIEx,y為(0.362,0.410)。

關鍵字

磷光系統 ； 螢磷混合系統 ； 螢光系統 ； 雙主發光體結構 ； 混合式主發光體結構 ； 共摻雜 ； 間隔層

並列摘要

This study is carried out to discuss how to reduce the driving voltage of blue phosphorescent organic light-emitting diodes (PHOLEDs) by using a thin double-emission layer. Experimental results show that when TCTA (10 nm) is used as the buffer layer, the luminance efficiency of the blue device increases up to 35.1 cd/A at a luminance of 1000 cd/m2, the power efficiency reaches 25.6 lm/W, and the operating voltage of 4.4 V. Furthermore, in this study, we also utilize the interface between double light-emitting layers of devices by codoping them with a red phosphorescent dopant [Os(bpftz)2(PPh2Me)2]. An Os complex with a high-lying highest occupied molecular orbital (HOMO) energy level (trapping holes) is codoped at the interface between emitting layers and an exciton-formation zone is expanded to obtain a white PHOLED with high efficiency. From the results, the optimal structure of the white device exhibits a operating voltage of 4.9 V, a current efficiency of 34.4 cd/A, a power efficiency of 22.0 lm/W, and Commission Internationale de L’Eclairage (CIE) coordinates of (0.328, 0.377) at a luminance of 1000 cd/m2. The CIE coordinates shited form 4 to 10 V is (∆x=+0.005, ∆y=+0.004). Furthermore, the power efficiency can be improved to 30.4 lm/W by attaching the outcoupling enhancement film.
PHOLEDs with high efficiency and low driving voltage were achieved by incorporating an electron transport material (3TPYMB) into a hole transport-type host (TCTA) as a mixed-host structure. For electrons, the emitting layer is nearly barrier-free until they reach the region of exciton formation, which keeps the driving voltage low. As the results shown, when the thickness of ETL was adjusted to 50 nm, it exhibited the driving 4.2 V, yield of 36.0 cd/A, and power efficiency of 27.5 lm/W at a luminance of 1000 cd/m2. Through the results of above, Os is doped in the middle of the mixed-host. White PHOLED exhibits current efficiency of 36.1 cd/A, and power efficiency of 26.4 lm/W. The CIE coordinates shited form 4 to 10 V is (∆x=+0.019, ∆y=+0.005). Furthermore, the power efficiency can be improved to 35.0 lm/W, and luminance efficiency to 46.8 cd/A by attaching a brightness enhancement film (BEF).
In this research complex emitting layers were fabricated using TCTA doping hole-transport material in the front half of bipolar 26DCzPPy as well as PPT doping electron-transport material in the back half of 26DCzPPy. Blue dopant FIrpic was also mixed inside the complex emitting layer to produce a highly efficient blue phosphorescent organic light emitting diode. The hole and electron injection and carrier recombination rate were effectively increased. The fabricated complex emitting layers exhibited current efficiency of 41.7cd/A, and power efficiency of 30 lm/W. A white OLED component was then manufactured by doping red dopant [Os(bpftz)2(PPh2Me)2] (Os) in proper locations. When the Os dopant was doped in between the complex emitting layers, excitons were effectively confined within, increasing the recombination rate and therefore reducing the color shift. The resulting CIE coordinates shifted from 4 to 10 V is (∆x=-0.004, ∆y=+0.001). The component had a current efficiency of 35.7 cd/A, a power efficiency of 24 lm/W. Attaching an outcoupling enhancement film was applied to increase the luminance efficiency to 30 lm/W.
Hybrid white organic light emitting diodes (HWOLEDs) with fluorescence and phosphorescence hybrid structures are studied in this work. HWOLEDs were fabricated with blue/red emitting layers: fluorescent host material doped with sky blue material, and bipolar phosphorescent host emitting material doped with red dopant material. Spacer layers were also inserted to expand the recombination zone, increase efficiency and reduce energy quenching along with roll-off effects. The resulting high efficiency warm white OLED device has the lower highest occupied molecule orbital level red guest material, current efficiency of 17.5 cd/A, and power efficiency of 12.5 lm/W, and CIE coordinates of (0.362,0.410) at a luminance of 1000 cd/m2.

並列關鍵字

phosphorescent system ； fluorescent-phosphorescent system ； fluorescent system ； double host structure ； hybrid host structure ； co-doped ； spacer layer

參考文獻

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