高效率與高演色性白光有機發光二極體之研究

Abstract

在顯示器或照明之應用上，Organic light-emitting diode面板是一個相當具有前景的新興科技。本研究首先製作四波段的螢光白光元件，除了原本的三原色，另外加了黃光的成分，以期能夠更加提高人眼的敏感性。雖然演色性可以達到87，然而過低的效率可能不足以應用在照明之上。故另搭配磷光材料提升效率，並同時又保有足夠的演色性，實驗結果發現以螢光藍搭配磷光紅、綠材料可以得到高達13.5cd/A的效率，同時也擁有超過80的演色性，足夠用於一般的照明應用之上。本研究另以螢光增感劑置放於元件結構之內，並利用磷光綠光與螢光紅光之間的不完全轉移，得到高達16.7cd/A的效率。最後，我以單色藍光OLED 搭配一外部色轉換層(External color tuning layer)以形成白光OLED 元件。此種方式提供了一簡化的方法以形成白光OLED 元件，也是目前製作白光LED的最主要方法。本研究發現以螢光藍光搭配色反轉材料可以達到白光原點的光色。另外搭配使用藍光磷光材料之非漸層式以及漸層式(Graded)的元件，研究結果發現漸層式的元件具有最好的效率，磷光藍光FIrpic一單色光元件利用獨特的漸層式做法，可以提升40%的效率。

OLED panels might become a booming future for next generation displays or solid state lighting. This study fabricated a highly efficient and improved color rendering index white OLED device with a “tetra-chromatic” emission system. The device achieved a CRI of 87, and is tuneable from the twilight to daylight sky color. However, due to the low efficiencies, phosphorescent based device structures were hence developed. A fluorescent blue plus phosphorescent green and red emission layer device is demonstrated to have an efficiency of 13.5 cd/A and color rendering index over 80, which is acceptable for illumination. We also adopted a phosphorescent sensitizer to excite a fluorescent dye through resonant energy transfer by replacing the phosphorescent red material Ir(piq)3 into a fluorescent red material DCJTB. By using this mechanism and by inefficient transfer from the green to red, a higher efficiency of 16.7 cd/A was reached due to the higher eye sensitivity of the orange-reddish emission color of DCJTB. Finally, an external color tuning layer to simplify the fabrication process of white devices by using a blue device plus yellow down conversion layer, which is a common technology in LED industry was developed. By the concept of complementary colors, these two colors produced white emission. In this part, we also studied the effect of graded devices, and found that a graded phosphorescent blue device provided a higher efficiency.