Abstract
High efficiency is important for successful deployment of any light sources. Continued efforts have recently made it possible to demonstrate organic light-emitting diodes with efficiency comparable to that of inorganic light-emitting diodes. However, such achievements were possible only with the help of a macroscopic lens or complex internal nanostructures, both of which undermine the key benefits of organic light-emitting diodes as an affordable planar light source. Here we present a systematic way to achieve organic light-emitting diodes with ultrahigh efficiency even only with an external scattering film, one of the simplest low-cost outcoupling structures. Through a global, multivariable analysis, we show that scattering with a high degree of forwardness has a potential to play a critical role in realizing ultimate efficiency. Combined with horizontally oriented emitters, organic light-emitting diodes equipped with particle-embedded films tailored for forward-intensive scattering achieve a maximum external quantum efficiency of 56%.
Highlights
High efficiency is important for successful deployment of any light sources
We explored a systematic way to achieve an external quantum efficiency (EQE) of 50% or higher in organic light-emitting diodes (OLEDs) that employ only an external scattering medium rather than resorting to a macroscopic lens or complex internal structuring
Thanks to the equation-based nature of radiative transfer theory (RTT), a facile global optimization could be done while simultaneously taking into account several variables for OLED stacks and scattering layers
Summary
High efficiency is important for successful deployment of any light sources. Continued efforts have recently made it possible to demonstrate organic light-emitting diodes with efficiency comparable to that of inorganic light-emitting diodes. Unlike the Monte-Carlo approach, in which individual scattering events and successive light propagations are traced for every step[21], RTT takes advantages of the statistical nature of multiple scattering processes and describes their average effect on intensity change via a well-defined set of equations[22] This equation-based character of the RTT makes it easy to combine, in a trans-scale fashion, with an optical model for light emission within an OLED, which may be generalized as radiative emission from a dipole in a thin-film multilayer stack. Tailoring the characteristics of particle-embedded scattering layers such as asymmetry parameter, scattering efficiency, and scatterance is shown to play a key role in utilizing the full potential offered by the external scattering methods
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