以有限時域差分法模擬發光元件之發光效率

Abstract

在本論文中，我們以三維有限時域差分法模擬發光元件之發光效率，並且加入光子晶體結構以改良其發光效率。 光波在發光元件如有機發光二極體或發光二極體中，會因為折射率差異發生全反射而侷限在其內部。我們以有限時域差分法為基礎來模擬光波在元件內的情形，並計算可見光的發光效率。 有限時域差分法具有容易推導且方便計算複雜結構的優點。但是為了處理有機發光二極體內的金屬電極以及內部的微結構，我們必須再做上一些修正。以Drude model去近似光波在金屬電極的行為，並且搭配近遠場轉換及幾何光學，求得最後光波穿透到空氣的能量。而因為有限時域差分法模擬時需極大的運算資源，因此我們使用平行運算或交替方向隱式差分來改良之。 為了提高發光元件的發光效率，我們改變有機發光二極體結構厚度或在全反射的介面加入光柵結構。藉由光波在週期性結構的散射行為，使光波能夠耦合到有機發光二極體外。最後將發光二極體做成光子晶體結構，改變其結構的半徑周期比與厚度，利用光子晶體的能隙的設計，使光波耦合到空氣中，以提升發光二極體發光效率。

In this thesis, we use three dimensional finite-difference time-domain (FDTD) method to simulate the extraction efficiency of light emitting devices and improve the extraction efficiency by applying photonic crystal structure. Light wave in light emitting devices, such as organic light-emitting diodes (OLED) or light emitting diodes (LED), is confined when total internal reflection occurs due to difference of refractive index in each layer. We simulate behavior of light in these devices and evaluate the extraction efficiency of each based on FDTD. The advantages of FDTD are easy derivation and convenience for complex structure design. However, some modification is essential for the metal cathode and inner micro-structures in OLED. We use the Drude model to approximate the light behavior in the metal and evaluate the energy penetrating to air using near-to-far-field transformation and geometric optics. Parallel programming and alternating-direction-implicit difference are also used to improve calculation efficiency since FDTD simulation requires a huge amount of calculation resource. To enhance the extraction efficiency of OLED, we modify the thickness of layers of OLED and insert the grating structures between the layers. Light is scattered to air due to the grating structure. Finally, we apply photonic crystal structures on LED with different radius-period ratio and thickness. By manipulating the photonic bandgap, light will be coupled to air, resulting in high extraction efficiency.