Frustrated total internal reflection in organic light-emitting diodes employing sphere cavity embedded in polystyrene

Abstract

The light extraction efficiency of top-emitting organic light-emitting diodes (OLEDs) is numerically investigated employing the finite-difference time-domain method. The periodic nanostructures formed by embedding the sphere arrays in polystyrene (PS) are placed on top of OLED to frustrate the total internal reflection at the interface between OLED and free space. These nanostructures serve as an intermediate medium to extract the light out of OLED devices. Efficiently coupling both evanescent waves and propagation waves into spheres and subsequently extracting these light waves out of the sphere is key to achieving high extraction efficiency. By tuning the thickness of PS layer, both of the in-coupling efficiency and out-coupling efficiency are optimized for achieving high light extraction efficiency. Thicker PS layer results in higher in-coupling efficiency in sphere while the thinner PS layer leads to higher out-coupling efficiency. Thus the maximum light extraction is a trade-off between the in-coupling efficiency and out-coupling efficiency. The study shows that light extraction efficiency of 89% can be achieved by embedding 0.90 μm TiO2 sphere in 0.30 μm PS layer with optimized in-coupling efficiency, out-coupling efficiency and cavity effect.

Light Extraction Efficiency Analysis of Flip-Chip Ultraviolet Light-Emitting Diodes With Patterned Sapphire Substrate

“…1). Single dipole source is used in this work as the use of multiple dipole sources will result in non-physical interference pattern [42], which is undesirable for analysis of the optical properties of LEDs. A source power monitor surrounding the dipole source is used to measure the total power generated in the active region while one output power monitor is placed at distance λ away from the sapphire top surface to measure the light output power radiated out of the LED structure.…”

Effect of HfO2 Passivation Layer on Light Extraction Efficiency of AlInN Nanowire Ultraviolet Light-Emitting Diodes

“…In this study, the LEE of the AlInN NW UV LEDs is estimated using the threedimensional (3D) FDTD computational method (10). The AlInN NW UV LED structure grown on Si substrate is composed of 200 nm n-GaN, 100 nm n-Al x In 1-x N quantum barrier (QB), 40 nm i-Al y In 1-y N quantum well (QW), 100 nm p-Al x In 1-x N QB, and 20 nm p-GaN layer.…”

Enhancing Light Extraction Efficiency of Vertical Emission of AlGaN Nanowire Light Emitting Diodes With Photonic Crystal

“…In the FDTD simulation, a single dipole source is positioned in the middle of active region, which is a commonly used approach in LED simulation [22], [34], [35]. Although a single dipole source is placed at the central nanowire in the simulation region, the electric field can effectively spread across the entire LED structure due to the periodicity of nanowires array, as shown in Fig.…”