Nanowires brighten up organic LEDs


台灣的科學家發現,使用奈米線可將有機發光二極體(OLED)的發光效率提升至45%,而且奈米線還能取代昂貴的氧化銦錫(indium tin oxide, ITO)透明電極,作為元件的陽極。這項技術除了能提升液晶顯示器(LCD)的亮度外,甚至連濾光片都可能免了。


Nanowires can enhance the light-emitting efficiency of organic LEDs by up to 45%, say researchers in Taiwan. An added bonus is that the nanowires could replace expensive indium tin oxide as the anode in such devices. The technique might even be applied to liquid crystal displays to increase their brightness and possibly eliminate the need for colour filters.

OLED由於製造容易,被視為次世代顯示器與照明的明日之星。雖然OLED在許多方面的效能比一般非有機LED好,但其發光效率很低,約只有20%左右,原因是全反射使得大部分的光都侷限在透明基板與組成OLED的有機層中。


Organic light emitting devices (OLEDs) are promising for next-generation displays and lighting because they are simple to make. Although OLEDs are better than conventional inorganic LEDs in many ways, they do suffer from a low light-emitting efficiency of around 20%. This is because most of the light is trapped (due to total internal reflection) in the transparent substrate and the organic layers making up the devices.

先前提高發光效率的方法是採用介電質微結構或表面粗化。中央研究院應用科學研究中心的魏培坤等人,發現將厚50 nm的金奈米線陣列放置在透明電極上,可使Alq3製成的OLED發光強度提高2倍。這些奈米線的功能如同光散射器,每個陣列相隔450 nm。該間隔週期與放射光的最大波長相匹配,因此可以增加光輸出強度。


Previous research extracted this trapped light by using dielectric microstructures or roughing the surface. Now, Pei-Kuen Wei of the Research Center for Applied Science in Taipei and colleagues have found that an array of 50 nm thick gold nanowires placed on top of an indium tin oxide (ITO) anode can increase the light-emitting intensity of an OLED made from Alq3 by up to two times. The nanowires, which act as light scatterers, are placed 450 nm apart in the arrays. This period matches the peak emission wavelength of the emitted light, which enhances light extraction.

魏培坤表示,金奈米線陣列具既導電又高度透明,可用來取代價格較昂貴的ITO。使用金屬奈米線陣列將光有效地從基板萃取出的概念,也能應用到LCD上。使用薄玻璃或PMMA板來導光的新型液晶背光模組也可因散射而提高亮度。此外,由於散射光的波長取決於奈米線陣列的週期,因此不用彩色濾波片,只要藉著改變奈米線的週期就能直接由導光板產生紅、綠、藍三原色。


Wei told nanotechweb.org that the gold nanowire arrays might be used to replace expensive ITO in OLEDS because they are conducting and have a high optical transmission. "The concept of using metallic nanowire arrays for efficiently extracting light from a substrate could also be applied to LCDs," he added. Modern liquid crystal backlights use a thin glass or PMMA plate to guide light that may also benefit from light scatterers. Moreover, since the wavelength of the light scattered depends on the periodicity of the nanowires in the arrays, it might be possible to produce red-green-blue colours directly from the guiding plate without using colour filters, he said.

上述研究團隊正試著找出萃取光的最佳化奈米結構,他們也將嘗試二維奈米結構(如正方或六角形的奈米點)以及其他金屬材料(例如銀)。詳見Appl. Phys. Lett. 92, 013303 (2008)。


The team is now trying to find the optimal nanostructures for light extraction. It will also test various 2D periodic nanostructures, such as square or hexagonal nanodots, and other metals like silver.


The work was reported in Appl. Phys. Lett.


原始網站: http://nanotechweb.org/cws/article/tech/33044

譯者:謝德霖(逢甲大學光電學系)

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