Top-emitting organic light-emitting diodes: Influence of cavity design

Hofmann, Simone; Thomschke, Michael; Freitag, Patricia; Furno, Mauro; Lüssem, Björn; Leo, Karl

doi:10.1063/1.3530447

Cited by 109 publications

(81 citation statements)

References 21 publications

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“…The planar topemitting OLED (Device A) reaches 15 % EQE at low current density. This value is comparable to literature reports on the most efficient single-color top-emitting OLEDs operating in the second optical maximum [3]. Compared to the planar reference, Device B (Λ B, mask = 1.0 µm) shows an enhanced EQE over the entire current range investigated.…”

Section: Performance Of Top-emitting Oleds On Periodically Corrugatedsupporting

confidence: 75%

“…However, even for OLEDs with an internal quantum efficiency of nearly 100 % [6], the maximum external quantum efficiency achieved up to now for a planar device layout without light outcoupling structure is only approximately 30 % [3]. This results from the trapping of the majority of generated light within the device, e.g.…”

Section: Introductionmentioning

confidence: 99%

“…Top-emitting OLEDs are very interesting candidates in this context as they combine high efficiency and compatibility with pre-processed backplane driver electronics and roll-to-roll manufacturing schemes on flexible, opaque substrates, such as metal foils. It has been shown that single color top-emitting OLEDs can easily surpass the efficiency of their bottom-emitting counterparts [3] and that white top-emitting can at least achieve similar efficiency [4,5].…”

Section: Introductionmentioning

confidence: 99%

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Coherent mode coupling in highly efficient top-emitting OLEDs on periodically corrugated substrates

Schwab¹,

Fuchs²,

Scholz³

et al. 2014

Opt. Express

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Abstract:Bragg scattering at one-dimensional corrugated substrates allows to improve the light outcoupling from top-emitting organic light-emitting diodes (OLEDs). The OLEDs rely on a highly efficient phosphorescent pin stack and contain metal electrodes that introduce pronounced microcavity effects. A corrugated photoresist layer underneath the bottom electrode introduces light scattering. Compared to optically optimized reference OLEDs without the corrugated substrate, the corrugation increases light outcoupling efficiency but does not adversely affect the electrical properties of the devices. The external quantum efficiency (EQE) is increased from 15 % for an optimized planar layer structure to 17.5 % for a corrugated OLED with a grating period of 1.0 µm and a modulation depth of about 70 nm. Detailed analysis and optical modeling of the angular resolved emission spectra of the OLEDs provide evidence for Bragg scattering of waveguided and surface plasmon modes that are normally confined within the OLED stack into the air-cone. We observe constructive and destructive interference between these scattered modes and the radiative cavity mode. This interference is quantitatively described by a complex summation of Lorentz-like resonances.

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Section: Performance Of Top-emitting Oleds On Periodically Corrugatedsupporting

confidence: 75%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Coherent mode coupling in highly efficient top-emitting OLEDs on periodically corrugated substrates

Schwab¹,

Fuchs²,

Scholz³

et al. 2014

Opt. Express

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show abstract

“…For top-emitting OLEDs without any further outcoupling techniques, the first order optical microcavity incorporating a large SPP contribution was found to be more efficient than optical microcavities exhibiting higher order WG modes. 18,19 Lately, anisotropic emitter materials showing a preferred spatial orientation of their transition dipole moment received great attention. 15,20,21 Using such materials, the efficiency limit can be increased compared to isotropic emitters.…”

Section: 3-5mentioning

confidence: 99%

Enhanced light emission from top-emitting organic light-emitting diodes by optimizing surface plasmon polariton losses

et al. 2015

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We demonstrate enhanced light extraction for monochrome top-emitting organic light-emitting diodes (OLEDs). The enhancement by a factor of 1.2 compared to a reference sample is caused by the use of a hole transport layer (HTL) material possessing a low refractive index (∼ 1.52). The low refractive index reduces the in-plane wave vector of the surface plasmon polariton (SPP) excited at the interface between the bottom opaque metallic electrode (anode) and the HTL. The shift of the SPP dispersion relation decreases the power dissipated into lost evanescent excitations and thus increases the outcoupling efficiency, although the SPP remains constant in intensity. The proposed method is suitable for emitter materials owning isotropic orientation of the transition dipole moments as well as anisotropic, preferentially horizontal orientation, resulting in comparable enhancement factors. Furthermore, for sufficiently low refractive indices of the HTL material, the SPP can be modeled as a propagating plane wave within other organic materials in the optical microcavity. Thus, by applying further extraction methods, such as micro lenses or Bragg gratings, it would become feasible to obtain even higher enhancements of the light extraction.

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“…This enhances light outcoupling to some extent, even though it does not completely solve the problem of TIR. [10][11][12] Thomschke et al 13 demonstrated the lamination of a high refractive index microlens foil on top of a white OLED and obtained a device efficacy of over 30 lm/W (27% EQE). Recently, Kim et al achieved an EQE of 44.7% (1.8-fold enhancement) for a green top-emitting OLED using a microlens array that was fabricated by evaporating an organic capping layer through a shadow mask.…”

mentioning

confidence: 99%

White top-emitting organic light-emitting diodes with solution-processed nano-particle scattering layers

Schaefer

Schwab

Lenk

et al. 2015

Applied Physics Letters

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A random scattering approach to enhance light extraction in white top-emitting organic light-emitting diodes (OLEDs) is reported. Through solution processing from fluorinated solvents, a nano-particle scattering layer (NPSL) can be deposited directly on top of small molecule OLEDs without affecting their electrical performance. The scattering length for light inside the NPSL is determined from transmission measurements and found to be in agreement with Mie scattering theory. Furthermore, the dependence of the light outcoupling enhancement on electron transport layer thickness is studied. Depending on the electron transport layer thickness, the NPSL enhances the external quantum efficiency of the investigated white OLEDs by between 1.5 and 2.3-fold. For a device structure that has been optimized prior to application of the NPSL, the maximum external quantum efficiency is improved from 4.7% to 7.4% (1.6-fold improvement). In addition, the scattering layer strongly reduces the undesired shift in emission color with viewing angle.

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Top-emitting organic light-emitting diodes: Influence of cavity design

Cited by 109 publications

References 21 publications

Coherent mode coupling in highly efficient top-emitting OLEDs on periodically corrugated substrates

Coherent mode coupling in highly efficient top-emitting OLEDs on periodically corrugated substrates

Enhanced light emission from top-emitting organic light-emitting diodes by optimizing surface plasmon polariton losses

White top-emitting organic light-emitting diodes with solution-processed nano-particle scattering layers

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