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Measured angular dependent emission spectra for s-and p-polarized light of planar (a-b) and corrugated topemitting OLED (c-d) operating in the second optical maximum. Bragg scattering at the one dimensional shallow sub-µm grating superimposes sharp spectral features to the resonant cavity emission, resulting from constructive and destructive interference of the cavity emission and Bragg scattered modes.
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Bragg scattering by one dimensional periodic structures is investigated in order to enhance the outcoupling efficiency of optically optimized planar top-emitting OLEDs. Using a soft imprint process, we fabricate extremely homogeneous gratings with sub-mu m period. These gratings are integrated beneath the bottom contact of top-emitting OLEDs, witho...
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Citations
... However, it had a slight effect on the light emitted at the target wavelength because the peak wavelength remained the same and the intensity of the shoulder peak was trivial. This is the effect of Bragg scattering caused by the periodic grating structure of the corrugated device [53,54]. Moreover, Figure 14b shows that the color purity improved in the planar-cavity (x = 0.338, y = 0.606) and corrugated-cavity (x = 0.333, y = 0.588) devices compared to the reference device (x = 0.369, y = 0.556). ...
... A photograph of the emission device is shown in Figure 14c. of the shoulder peak was trivial. This is the effect of Bragg scattering caused by the periodic grating structure of the corrugated device [53,54]. Moreover, Figure 14b shows that the color purity improved in the planar-cavity (x = 0.338, y = 0.606) and corrugated-cavity (x = 0.333, y = 0.588) devices compared to the reference device (x = 0.369, y = 0.556). ...
Luminous efficiency is a pivotal factor for assessing the performance of optoelectronic devices, wherein light loss caused by diverse factors is harvested and converted into the radiative mode. In this study, we demonstrate a nanoscale vacuum photonic crystal layer (nVPCL) for light extraction enhancement. A corrugated semi-transparent electrode incorporating a periodic hollow-structure array was designed through a simulation that utilizes finite-difference time-domain computational analysis. The corrugated profile, stemming from the periodic hollow structure, was fabricated using laser interference lithography, which allows the precise engineering of various geometrical parameters by controlling the process conditions. The semi-transparent electrode consisted of a 15 nm thick Ag film, which acted as the exit mirror and induced microcavity resonance. When applied to a conventional green organic light-emitting diode (OLED) structure, the optimized nVPCL-integrated device demonstrated a 21.5% enhancement in external quantum efficiency compared to the reference device. Further, the full width at half maximum exhibited a 27.5% reduction compared to that of the reference device, demonstrating improved color purity. This study presents a novel approach by applying a hybrid thin film electrode design to optoelectronic devices to enhance optical efficiency and color purity.
... Several technical approaches have been suggested to enhance the efficiencies. Relevant methods include external/internal structural and microcavity approaches [6][7][8]. Also, molecular orientation strategies have been explored to enhance the OLED efficiencies [9]. As an effort to enhance the efficiencies of the TOLEDs a capping layer has been widely applied on the surface of the thin metallic electrode [10]. ...
... Regarding the desired angular stable emission characteristics, we demonstrate the usefulness of wrinkles for achieving negligible viewing angle dependent EL spectra and enhancing the outcoupling efficiencies of TOLEDs. Our structural approach differs in terms of size and distribution with previous works [7]. Our wrinkles have submicron size and a random distribution. ...
Angular electroluminescence spectra stabilized and efficiency enhanced top-emitting organic light-emitting devices (TOLEDs) were demonstrated using randomly distributed mesoscopic internal wrinkles. Compared to planar TOLEDs, wrinkled TOLEDs showed a faster exciton decay rate in the emissive layer and high rate of radiative recombination, which leads to enhanced efficiency. Our wrinkled TOLEDs showed angular spectral dependency (u’v’(θ)) of 0.0032, which is low enough to be imperceptible to the human eyes, and 38.7 % enhanced external quantum efficiency relative to the planar counterpart. The approach described here provides an effective scheme for improving TOLEDs and obviating the necessity of modifying the stack structure of the device.
We demonstrate high efficiency light extraction for top-emitting organic light-emitting devices (OLEDs) comprising a transparent conductive oxide on the surface of a non-diffractive, reflecting metal-coated scattering grid located beneath the organic active region. The grid scatters light trapped in waveguide modes without changing the device electrical properties or causing significant plasmonic losses. This results in an increase in external quantum efficiency for green phosphorescent organic light-emitting devices from 20±1% to 30±2%, for structures without and with the reflecting grid. Adding a low refractive index capping layer reduces the spectral angular dependence characteristic of top emitting organic light emitting devices. The improvement in light extraction by substrate modification allows for optimization of the optical design without necessitating changes in the design or structure of the OLEDs themselves.
Active matrix for organic lightemitting diode (OLED) microdisplay is a complementary metal–oxide–semiconductor (CMOS) circuit. OLED-based microdisplays are made onto CMOS-built silicon wafers in cluster tools. A picture of an ALD system (Savannah system from Ultratech/Cambridge Nanotech) embedded into a glove box is depicted in this chapter, as well as the route to make the encapsulation process. One of the advantages of the color filters on glass is that the glass plays the double role of substrate and of protective cap. Such a protection is indeed highly recommended owing to the fragility of the OLED structure, even if color filters are deposited onto OLED. The chapter describes how to provide video and configuration data from an image source, e.g. computers and smartphones to microdisplays. It shows different technologies to mount and pack microdisplays on modules.
Two of the recent major research topics in optoelectronic devices are discussed: the development of new organic materials (both molecular and polymeric) for the active layer of organic optoelectronic devices (particularly organic light-emitting diodes (OLEDs)), and light management, including light extraction for OLEDs and light trapping for organic solar cells (OSCs). In the first section, recent developments of phosphorescent transition metal complexes for OLEDs in the past 3–4 years are reviewed. The discussion is focused on the development of metal complexes based on iridium, platinum, and a few other transition metals. In the second part, different light-management strategies in the design of OLEDs with improved light extraction, and of OSCs with improved light trapping is discussed.
