本研究利用一無電子注入能障之主體材料，搭配利於電洞注入之共主體 tris(2-phenylpyridine)iridium(III) [Ir(ppy)3]，並使用高發光效率之磷光黃光染料 iridium(III)bis(4-phenylthieno[3,2-c]pyridinato-N,C 2')acetylacetonate (PO-01)，有效使元件於高亮度下仍能保持高效率，並製備一突破世界紀錄之高效率黃光磷光有機發光二極體。元件效率表現，在亮度為 100 cd/m2 下，能量效率為79 lm/W，電流效率為77 cd/A，外部量子效率為25%，在亮度為1,000 cd/m2下，則分別為59 lm/W，71 cd/A，以及23%。元件高效率的原因為：(1)使用薄發光層以及無電子注入能障主體，有效降低元件驅動電壓而達高效率；(2)使用共主體結構，使載子更易注入至發光層；於低電壓下，激子主要於共主體上產生，高電壓下則主要於主體上產生，使元件不論在低或高電壓下，皆能夠有良好的主客體能量傳遞，並於高亮度下仍能維持高效率。另外，選用不同性質之主體材料 (具電洞傳輸性或同時具電子電洞傳輸性)，搭配此共主體材料，於高亮度下，元件效率皆能獲得改善。

We demonstrate herein the design and fabrication of a highly efficient yellow organic light-emitting diode (OLED) with a balanced carrier injection device architecture having a zero electron-injection-barrier host blended with a hole-injection aiding co-host. The resultant yellow OLED showed, at 1,000 cd m-2 for example, an efficacy of 59 lm W-1, current efficiency of 71 cd A-1 and external quantum efficiency (EQE) of 23%, while 42 lm W-1, 47 cd A-1 and 15% EQE without co-host. The co-host effect that resulted in a much balanced carrier injection was also valid for other yellow OLED devices and their efficiency improvement was also very marked. With the use of a micro-lens, the device efficiency is further improved to 79 lm W-1, 96 cd A-1 and 30% EQE.

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