有機發光二極體(OLED)因為重量輕、厚度薄、具有更寬的視角和低操作電壓等優點而被視為次世代顯示器中關鍵的角色。近年來積極發展其潛在應用，如：平面顯示器和可彎曲螢幕。典型的OLED是將有機發光材料夾在陰陽兩極中間層狀堆疊在基板上。由於陽極層為高折射率介質(n=1.8)，發光層發出的光大部分都因其層狀界面產生之全內反射(TIR)而被限制在結構內，所以傳統的OLED其發光效益仍有限且低至20%。
光子晶體(photonic crystal)是由不同折射率之材料週期性排列而成的多維人造結構。經由適度的設計可具備控制光於其內傳遞的效果。光子晶體具有傳導模態和輻射模態，有別於傳導模態，若光波落在輻射模態(位於light cone之上的模態)，將無法在光子晶體內部傳導，會輻射到晶體外部(external mode)。利用此一性質，將光子晶體置入多層的發光結構中，例如：LED、OLED，可提升光的透射效率。
本文使用12重對稱阿基米德A7晶格之光子晶體嵌入玻璃基板中提升OLED的發光效率。此SiO2/SiNx 材料組成的二維光子晶體層可使光從有層/ITO層之高折射率介質產生的波導模態轉變為輻射模態。我們透過平面波展開法(PWEM)來設計光子晶體的參數並利用三維時域有限差分法(3D FDTD)加以模擬光子晶體OLED之透光效益。
模擬結果可分為兩部分，從電場圖和透射效率得知，利用阿基米德A7晶格，因其具有較密集之輻射模態和高對稱性，可減少光侷限在發光層之波導模態，有效提升光從發光層透射至玻璃層；透過遠場投影圖分析，針對不同視角之電場強度積分和不同蝕刻深度之增強效益比較，可知本設計相較於傳統光子晶體OLED的發光強度更高且集中並能降低製程所需的時間和成本。

Organic light-emitting diode(OLED) is considered as a critical component for next generation displays due to its light weight, thin thickness, wider viewing angles and low operational voltage. The OLED displays have been actively investigated in recent years on account of their potential applications in flat panel displays and flexible displays. A typical OLED is composed of a layer of organic materials situated between the anode and cathode, all deposited on a substrate. However, because of the high refractive index of the anode ITO layer(n=1.8), the light extraction efficiency of a conventional OLED is still limited to be as low as 20%, which is one of the most important issues for practical device applications. The low efficiency arises from that most of the emitted light is confined inside the device due to the total internal reflection(TIR) at the interfaces of the layers.
Photonic crystals(PhCs) are artificial multi-dimensional periodic structures with periodic modulation of the refractive index. Suitably designed, PhCs have the ability to control the propagation of light. The PhCs have both guide and radiation modes. The guide mode allows the lights to transmit internally. In contrast, the radiation mode refers to the phenomena in which the lights are not guided to transmit internally. Set the incident light in the radiation modes, then it would not propagate along the wave guide internally. Instead, the lights radiate and escape from the wave guide. By taking advantages of this feature, we can therefore enhance the efficiency of light extraction by embedding photonic crystals in the multiple structures, such as LED and OLED.
To improve light extraction from organic light-emitting diodes(OLED), we present a photonic crystal with 12-fold symmetry Archimedean A7 lattice into the glass substrate of an OLED. The two-dimensional SiO2/SiNx photonic crystal layer converts the guided waves in the high-refractive-index indium-tin-oxide(ITO)/organic layers into radiation waves. By using the plane wave expansion method(PWEM), we design the structural parameters of the photonic crystal pattern and the finite-difference time-domain(FDTD) method to simulate the light extraction from the PhC-OLED.
There are two parts of the simulation results, from the electric field and transmission, we can observe the lights transmit into glass layer form the organic emitting layer because of the Archimedean A7 lattice with higher order symmetry and density of states in the radiation mode; we compare the enhancement of light extractions by integrating the far-field projection over the viewing angles and different etching depths, it follows that this design would contribute to not only making OLED lights brighter and more concentrated but also consuming less process time and cost in comparison with conventional PhC-OLED.

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