光學結構於電致發光元件出光效率之提升

Abstract

近年來，由於有機發光二極體(OLED)及發光二極體(LED)等電致發光件(Electroluminescence devices)大量應用於LCD等顯示器或照明設備上，有輕薄，可撓式(flexible)等優點，。然而，其較低的出光效率仍是一個極需解決的問題。當光源從主動層(active layer)發出，大部分的光會侷限(trapped)在高折射率層中，導致出光效率低。且在基版(substrate)與空氣的介面上由於全反射的影響，部分的光會被反射回來，此亦為造成出光效率低的原因之一。為提升電致發光元 件的出光效率，在此我們利用二維光子晶體及微透鏡陣列等光學結構達到效率增加的目的。以光子晶體與微透鏡陣列分別應用於有機發光二極體(OLED)及發光二極體(LED)，以檢視奈米與微米等級的光學結構，在電致發光元件上所能提升的效率。根據模擬結果，將二維光子晶體結構應用於有機發光二極體上可得到1.17倍的提升。以微透鏡陣列應用於發光二極體上，則可得到1.35倍的效率增加。

Electroluminescent devices such as OLEDs and LEDs applied on flat panel display (ex. LCD) or lighting devices have the features of light weight and flexible. However, the low light extraction efficiency is one of the critical issues needed to be solved. When the light emitted from the active region, large portion of the light will be trapped inside the high-index layers which results in low extraction efficiency. Moreover, due to the total internal reflection effect at the interface between substrate and air, part of the light will be further reflected. As a consequence, only small portion of the emitted light will extract into the air. In order to enhance the light extraction efficiency of such electroluminescent devices, a two-dimensional photonic crystal structure and a microlens arrays are applied onto OLED and LED, respectively. An estimation of such nano and micro scale optical structures applied on lectroluminescent devices is made to see how the efficiency can be increased. According to our simulation result, 117% and 135% of enhancements in PC-OLED and microlens array based LED is obtained.