Fast and rigorous electromagnetic simulation of dipole emission in a periodically corrugated light-emitting diode structure based on diffraction tracking

Abstract

Organic light-emitting diodes (OLED) have become one of the major light sources for display use due to high color accuracy and luminosity. The external light efficiency of conventional OLEDs ranges around 20% while the internal quantum efficiency approaches ~100%, which is sufficiently low. The discrepancy arises from the total internal reflection and a relatively large refraction index of emission layers. It has been reported that the external light efficiency of an OLED can be improved by introducing a periodically corrugated layer boundary [1, 2], but the effect has not been analyzed quantitatively. Electromagnetic analysis of a dipole layer in a periodically corrugated LED has been done previously [3], but the approach used in that work cannot deal with the emission from a single dipole, which is crucial for analyzing a periodically corrugated dipole layer. In this work, we demonstrate how the emission from a single dipole in a periodically corrugated LED structure can be calculated by diffraction tracking. We decomposed the light emission of a point dipole source into plane waves, and tracked each wave to calculate light emission. We tracked the diffraction and polarization conversion at a periodically corrugated layer boundary. Diffraction efficiency was calculated by rigorous coupled-wave analysis method (RCWA) [4]. We have confirmed that the results from our calculation model agree well with the simulation values from finite-difference time-domain method (FDTD) in terms of far-field image and light extraction efficiency (LEE) while alleviating the computational load by a significant amount. We even showed that the results from our calculation model agree well with FDTD methods at two-dimensional periodically corrugated layer boundary. We also implemented direct calculation of incoherent dipole layer in a periodically corrugated OLED, which makes our method more time efficient. The advantages of our method become clear during the OLED structure optimization process. The diffraction coefficients obtained from the RCWA calculation depends only on the shape of the corrugation, hence the calculation for different dipole vertical/horizontal position, dipole orientation and different emission layer thicknesses can be completed with minimal computation. Also, the analysis involving multiple dipoles can be calculated in parallel, facilitating the optimization task even more.