應用新型主發光體系統之高效率紅色摻雜型有機電激發光元件

Abstract

在本篇論文中，我們將重新探討摻雜4-(dicyanomethylene)-2-t-butyl-6- (1,1,7,7-tetramethyl-julolidyl-9-enyl)-4H-pyran（DCJTB）的紅色有機電激發光元件（OLED），意欲透過元件結構的細部調整，達到簡化現行製程技術及增益元件效能的目的。我們發現只要透過更換電洞注入層材料、調整電洞傳輸層膜厚以及改變DCJTB摻雜濃度等作法，在不需要再額外摻入助發光體材料（Rubrene）的情況下，就可以獲得發光效率達2.52 cd/A及發光顏色達CIEx,y=（0.641, 0.356）的高效率紅光元件。具推測造成元件的發光效率獲得大幅增益的原因應來自於微共振腔光學效應、元件結構最適化及平衡載子注入效率等效應所造成的綜合效果。 除此之外，我們更進一步發展了一組新型的主發光體系統，將之應用於DCJTB元件中可以獲得在操作電流20 mA/cm2下，發光效率高達4.44 cd/A、操作電壓為6.77 V，並且顏色達CIEx,y=（0.65, 0.35）的飽和紅光元件。同時，這組由Rubrene/Alq3構成發光層所製成的DCJTB元件，成功排除了原先在高趨動電流時會損失發光效率的問題，以致能夠獲得平坦的操作電流密度（J）–發光效率（cd/A）曲線；以上種種優點均將十分有利於製作被動式或主動式驅動的全彩平面顯示器。

In this thesis, we have studied the device optimization of red 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyl-julolidyl-9-enyl)-4H-pyran（DCJTB）dye doped Alq3 emitters in OLED. By varying the hole injection materials and thickness of hole-transport layer, efficiency of 2.52 cd/A and near saturated CIE color coordinates of x = 0.641, y = 0.356 was achieved without needing additional doping of emitting assist dopant (rubrene). From experiments with film thickness variation, it is concluded that the improved EL performance and color saturation are due to the synergistic effects of microcavity, device structural optimization as well as optimal doping of DCJTB. Furthermore, we have also developed what appears to be one of the highest luminance efficiency ever reported for the archetypical DCJTB doped red emitter at 4.44 cd/A at 20 mA/cm2 and 6.77 V with a near saturated CIEx,y red color coordinate of [0.65, 0.35]. By doping DCJTB into the novel co-host matrix emitting system of rubrene/Alq3, we have also successfully eliminated the problem of luminescence quenching at high drive voltage and achieved a “flat” cd/A vs J response that is highly desirable for passive as well as active matrix full color OLED flat panel display applications.