Employing a 2D surface grating to improve light out coupling of a substrate emitting organic LED

Abstract

We present simulation and experimental results to achieve increased light extraction of a substrate emitting OLED. We present a comparison between a grating surface on the OLED and an array of microlenses at the interface between substrate and air. This experimentally gives -in both cases-a relative improvement of approx. 30 %. We also demonstrate the concept of a RC 2 LED, applied to an OLED. The RC 2 LED is composed by adding a high, low and high index layers between ITO and glass, i.e. the interface between organic layers and glass. These extra layers create a cavity which numerically gives a relative improvement of over 60% at the resonance wavelength of the cavity over a wavelength range of 50-100 nm. The influence of an array of micro lenses in addition to the RC 2 layers is also investigated in this paper.

Enhancing the Out-Coupling Efficiency of Organic Light-Emitting Diodes Using Two-Dimensional Periodic Nanostructures

“…From the simulation results, it was found that the surface PhCs play a poor role in enhancing the out-coupling efficiency of the OLEDs (about 120%). In the experiment, the enhancement factor F of about 130% with surface PhCs was obtained [21].…”

Improved light extraction in the bioluminescent lantern of a Photuris firefly (Lampyridae)

“…It should be noted that with these refractive indexes, the critical angle for total reflection is 40 • , as given by (8), so that none of the incidence angles θ i between 40 • and 90 • contribute to the transmission. At small angles, for θ i near 0 • , the geometric factor sin θ i also cuts the transmission efficiency, even if the Fresnel's transmission coefficient is strong there (about 95%).…”

“…When a source emits from inside a high refractive index medium, the emitted light that reaches the surface will not always be able to escape into the air, because of the total reflection at large incidence angles. The external efficiency of all electroluminescent devices made from semiconductors [7] is affected by this effect, and this is especially true for the recently developed large-size organic light-emitting diodes [8,9]. The firefly lantern is no exception and it is interesting to parallel the decades of semiconductor diodes structural optimized engineering with some hundred million years of blind natural selection in these living organisms.…”

Improved light extraction in the bioluminescent lantern of a Photuris firefly (Lampyridae)

“…This result may seem surprisingly low, especially for a medium with a very moderate refractive index, such as the one considered here. It should be noted that with these refractive indexes, the critical angle for total reflection is 40 • , as given by (8), so that none of the incidence angles θ i between 40 • and 90 • contribute to the transmission. At small angles, for θ i near 0 • , the geometric factor sin θ i also cuts the transmission efficiency, even if the Fresnel's transmission coefficient is strong there (about 95%).…”

“…When a source emits from inside a high refractive index medium, the emitted light that reaches the surface will not always be able to escape into the air, because of the total reflection at large incidence angles. The external efficiency of all electroluminescent devices made from semiconductors [7] is affected by this effect, and this is especially true for the recently developed large-size organic light-emitting diodes [8,9]. The firefly lantern is no exception and it is interesting to parallel the decades of semi-conductor diodes structural optimized engineering with some hundred million years of blind natural selection in these living organisms.…”