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

Schwab, Tobias; Fuchs, Cornelius; Scholz, Reinhard; Zakhidov, Alex; Leo, Karl; Gather, Malte C.

doi:10.1364/oe.22.007524

Cited by 67 publications

(61 citation statements)

References 35 publications

(11 reference statements)

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“…Figure 5 shows mode profiles of the lowest-order waveguided and plasmonic mode supported by a standard bottom-emitting OLED stack and how these modes can interact with a scattering structure located underneath the anode of the device. [58][59][60] However, in general, these photonic structures are wavelength selective, which is why they are difficult to apply in broadband white OLEDs. 40 and 55) and PEDOT/PSS anodes.…”

Section: Wavelength-independent Scattering-based Outcoupling Approachesmentioning

confidence: 99%

Recent advances in light outcoupling from white organic light-emitting diodes

2015

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Organic light-emitting diodes (OLEDs) have been successfully introduced to the smartphone display market and have geared up to become contenders for applications in general illumination where they promise to combine efficient generation of white light with excellent color quality, glare-free illumination, and highly attractive designs. Device efficiency is the key requirement for such white OLEDs, not only from a sustainability perspective, but also because at the high brightness required for general illumination, losses lead to heating and may, thus, cause rapid device degradation. The efficiency of white OLEDs increased tremendously over the past two decades, and internal charge-to-photon conversion can now be achieved at ∼100% yield. However, the extraction of photons remains rather inefficient (typically <30%). Here, we provide an introduction to the underlying physics of outcoupling in white OLEDs and review recent progress toward making light extraction more efficient. We describe how structures that scatter, refract, or diffract light can be attached to the outside of white OLEDs (external outcoupling) or can be integrated close to the active layers of the device (internal outcoupling). Moreover, the prospects of using top-emitting metal-metal microcavity designs for white OLEDs and of tuning the average orientation of the emissive molecules within the OLED are discussed.

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Section: Wavelength-independent Scattering-based Outcoupling Approachesmentioning

confidence: 99%

Recent advances in light outcoupling from white organic light-emitting diodes

2015

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“…The theoretical discussion indicates that in the best case the modified SPP can be modeled by a nonevanescent plane wave within the organic layers. Thus, it becomes an accessible target for further macroscopic 3,34 or microscopic 24,35 outcoupling techniques.…”

Section: 3-5mentioning

confidence: 99%

“…Furthermore it is worth to note that due to the oSPP shift, the excited modes are compressed into a smaller range of reciprocal space. This implies higher enhancement of such top-emitting OLEDs if Bragg scattering structures 24,35,50,51 are applied, because for one reciprocal lattice constant more modes can be scattered into the outcoupling cone. Moreover, as the in-plane wavenumber of the oSPP is reduced, the lattice constants for which the plasmon contribution is addressed can be increased compared to standard HTL materials.…”

Section: Optimizing Thin Film Spps and Power Dissipation Of Implemmentioning

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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“…In addition, the NPSL could be combined with internal scattering approaches such as periodic gratings to maximize the outcoupling efficiency. 8 …”

Section: -4mentioning

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

Cited by 67 publications

References 35 publications

Recent advances in light outcoupling from white organic light-emitting diodes

Recent advances in light outcoupling from white organic light-emitting diodes

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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