Light Extraction from Organic Light Emitting Diode Substrates: Simulation and Experiment

Greiner, H.

doi:10.1143/jjap.46.4125

Cited by 89 publications

(75 citation statements)

References 37 publications

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“…For typical white OLEDs, this refl ectivity stems from the metal back contact and assumes values of up to 90%. [ 9 ] Let us start our discussion by considering some simple cases. If the refl ectivity was ideal, i.e., 100% R = , and if the absorption was zero everywhere, one could simply add a homogeneously diffusive light-scattering layer with a suffi ciently large height h to homogenize the light emission.…”

Section: Full Paper Full Paper Full Papermentioning

confidence: 99%

Cloaking Contacts on Large‐Area Organic Light‐Emitting Diodes

Mayer

Schittny

Egel

et al. 2016

Advanced Optical Materials

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In this paper, we suggest a feasible way to homogenize the OLED light emission, i.e., to cloak the contacts or to make them "invisible" in emission. This task is schematically illustrated in Figure 1 . At fi rst sight, this task may appear the same as that of cloaking contact grids on the sunfacing side of solar cells. [ 8 ] These devices for solar cells operate in the regime of ballistic light propagation. [ 8 ] In sharp contrast, the cloaking devices for OLEDs described in the present paper operate in the distinct regime of multiple light scattering.We start in Section 2 by discussing two different blueprints based on the light-diffusion equation. The fi rst blueprint is based on coordinate transformations, leading to piecewise homogeneous and anisotropic diffusivities, the second blueprint uses piecewise homogeneous and isotropic diffusivities. The latter is postoptimized in Section 3 for large light throughput by using Monte-Carlo simulations, which can cover the regime between diffusive and ballistic light transport. Finally, the outcome is validated by model experiments in Section 4. Numerical Calculations Based on Light-Diffusion TheoryFigure 2 a illustrates the geometry of the problem considered in this paper. A homogeneous layer (yellow) emits light from its surface according to a Lambertian angular distribution. We assume that this layer is thin compared to all other dimensions.Metallic contact grids on top of large-area organic light-emitting diodes (OLEDs) are important for laterally homogenized current spreading leading to a lower series resistance and reduced large-scale brightness gradients. However, the contacts are also visible by unwanted shadows, i.e., by spatially inhomogeneous Lambertian light emission. In this paper, inspired by recent work on diffuse-light core-shell invisibility cloaking, a practical tailored distribution of light scattering centers is designed on top of an OLED to homogenize its light emission. Numerical solutions of the light-diffusion equation as well as Monte Carlo ray-tracing simulations are presented. The blueprint is verifi ed by experiments on a scaled-up model structure. The contacts can be made "invisible" in emission while maintaining large light throughput.

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Section: Full Paper Full Paper Full Papermentioning

confidence: 99%

Cloaking Contacts on Large‐Area Organic Light‐Emitting Diodes

Mayer

Schittny

Egel

et al. 2016

Advanced Optical Materials

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“…One common method is to couple the microscopic optical model with a ray-tracing software [9]. In this case, the emitted light distribution from the oscillating dipoles embedded in the thin film stack is taken as the starting point for modeling light propagation in the incoherent layer stack by raytracing simulations.…”

Section: Combining Setfos With a Ray-tracing Toolmentioning

confidence: 99%

P.151L: Late‐News Poster: Multi‐Scale Modeling of Organic Light‐Emitting Devices

Altazin

Perucco

Pagan

et al. 2013

Symp Digest of Tech Papers

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IntroductionModeling is an essential part in research of organic light-emitting devices (OLEDs) and speeds up their development. An accurate model can be used to gain further insight into device operation and for optimizing device performance. Difficulties to simulate state-of-theart commercialized OLEDs arise from the fact that these devices are not only made of an active thin-film layer stack, but also contain thick incoherent layers such as color filters or scattering layers that enhance the light out-coupling efficiency of the device. Moreover, the area of OLED devices for lighting applications can reach several square centimeters and potential losses within electrodes cannot be neglected. For the first time, we present a comprehensive model for OLEDs spanning from microscopic charge transport and exciton dynamics to large-area panels. Our approach is able to simulate the influence of electrical conductivity enhancement in large-area electrodes and light extraction enhancement induced by incoherent scattering layers or interfaces. In a first part of this paper we repeat the fundamentals of the microscopic model, previously implemented in the commercial simulation software SETFOS [1]. In the second part we introduce the macroscopic approach for optical and electrical modeling.

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“…Even though high internal quantum efficiencies can be achieved [3][4][5], external quantum efficiencies in OLEDs are much smaller due to the incomplete light extraction. Since the organic layers and the typically used ITO anode have an overall thickness of about 200 nm and feature high refractive indices in the range of 1.7 -2.1 [6,7], an organic light emitting diode (OLED) forms a slab waveguide. OLEDs are usually built on glass substrates with a refractive index of about 1.5.…”

Section: Introductionmentioning

confidence: 99%

White organic light emitting diodes with enhanced internal and external outcoupling for ultra-efficient light extraction and Lambertian emission

Bocksrocker¹,

Preinfalk²,

Asche-Tauscher³

et al. 2012

Opt. Express

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White organic light emitting diodes (WOLEDs) suffer from poor outcoupling efficiencies. The use of Bragg-gratings to enhance the outcoupling efficiency is very promising for light extraction in OLEDs, but such periodic structures can lead to angular or spectral dependencies in the devices. Here we present a method which combines highly efficient outcoupling by a TiO 2 -Bragg-grating leading to a 104% efficiency enhancement and an additional high quality microlens diffusor at the substrate/air interface. With the addition of this diffusor, we achieved not only a uniform white emission, but also further increased the already improved device efficiency by another 94% leading to an overall enhancement factor of about 4.

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Light Extraction from Organic Light Emitting Diode Substrates: Simulation and Experiment

Cited by 89 publications

References 37 publications

Cloaking Contacts on Large‐Area Organic Light‐Emitting Diodes

Cloaking Contacts on Large‐Area Organic Light‐Emitting Diodes

P.151L: Late‐News Poster: Multi‐Scale Modeling of Organic Light‐Emitting Devices

White organic light emitting diodes with enhanced internal and external outcoupling for ultra-efficient light extraction and Lambertian emission

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