Measuring and structuring the spatial coherence length of organic light‐emitting diodes

Xie, Guohua; Chen, Mingzhou; Mazilu, Michaël; Zhang, Shuyu; Bansal, Ashu K.; Dholakia, Kishan; Samuel, Ifor D. W.

doi:10.1002/lpor.201500065

Cited by 12 publications

(9 citation statements)

References 41 publications

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“…Figure 2b displays a ΔEL/EL map at 10 mT, which shows microscopic variations that are significant and spatially correlated on scales larger than those observed in the surface morphology of the active layer (Figure S5, Supporting Information) and fluctuations in the zero-field EL (Figure S7, Supporting Information), while also exceeding the spatial coherence lengths previously measured in similar OLEDs. [44,45] Structures observed in the magnetically enhanced EL maps also exhibit a high degree of correlation between successive field measurements up to a range of ≈2 mT and captured over times of 10 min (Figures S15 and S16, Supporting Information). This contrasts the time-correlated spatial fluctuations in EL at fixed magnetic fields, which plateau within ≈2 min (Figure S17, Supporting Information) and arise from photophysical processes within the material.…”

Section: Spatially Resolved Magneto-electroluminescencementioning

confidence: 79%

Resolving the Spatial Variation and Correlation of Hyperfine Spin Properties in Organic Light‐Emitting Diodes

et al. 2022

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under the application of relatively weak magnetic fields point toward their application as quantum sensors at room temperature. [17,18] Their fabrication flexibility and industrial use in commercial displays [19] underlie recent advances toward the miniaturization and integration of quantum technologies based on these materials. [20][21][22] For effective integration or miniaturization, reproducibility is crucial, and this extends to those properties of materials which impact spin-dependent processes. In this work, we aim to measure the variation of a critical spin property common to organic materials, the Overhauser field, which arises from the hyperfine coupling of charge-carrier spins to the bath of randomly oriented nuclear spins in the molecular environment. [23] The Overhauser field underlies a range of phenomena observed in organic devices, including magnetoresistive and magnetic resonant effects in organic light-emitting diodes (OLEDs), [24][25][26][27][28] both of which have been proposed as a mechanism to enable magnetic field sensing. [17,26] To date, the Overhauser field has been treated as a bulk property of the device, characterized by a single value that describes its impact. [26,29] If this is not a good assumption, it will present a significant challenge as we move toward high spatial resolution of magnetic fields [30,31] in organic devices. [32,33] We will demonstrate in the following sections that the Overhauser field indeed shows substantial intra-device variation by spatially resolving the magnetoluminescence effect exhibited by both a copolymer Super Yellow poly(phenylene-vinylene) (SY-PPV) and a small-molecule tris-(8-hydroxyquinoline) aluminum (Alq 3 ) OLED. As the Overhauser field is central to a wide range of spin-enabled functionality in organic devices, this variation presents a fundamental challenge for efforts to miniaturize and integrate such devices. Concept Magneto-Electroluminescence in OLEDsWe employ a stable and widely investigated active material-SY-PPV-to characterize the spatial variation of the Overhauser field in a simple vertical structure OLED (Figure 1a) and extract Devices that exploit the quantum properties of materials are widespread, with quantum information processors and quantum sensors showing significant progress. Organic materials offer interesting opportunities for quantum technologies owing to their engineerable spin properties, with spintronic operation and spin resonance magnetic-field sensing demonstrated in research grade devices, as well as proven compatibility with large-scale fabrication techniques. Yet several important challenges remain as moving toward scaling these proof-of-principle quantum devices to larger integrated logic systems or spatially smaller sensing elements, particularly those associated with the variation of quantum properties both within and between devices. Here, spatially resolved magnetoluminescence is used to provide the first 2D map of a hyperfine spin property-the Overhauser field-in traditional organic light-emitting diodes (...

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Section: Spatially Resolved Magneto-electroluminescencementioning

confidence: 79%

Resolving the Spatial Variation and Correlation of Hyperfine Spin Properties in Organic Light‐Emitting Diodes

et al. 2022

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“…However, the percentage of transmission for OLEDs is almost double compared to LEDs (Fig. 2e, Table S1) for both yellow and red, even though LEDs have a higher coherence length and are thus expected to have better penetration through skin 20,21 . OLEDs have a coherence length shorter than 2 μm whereas LEDs have a coherence length of ~12 μm 20,21 .…”

Section: Resultsmentioning

confidence: 99%

“…2e, Table S1) for both yellow and red, even though LEDs have a higher coherence length and are thus expected to have better penetration through skin 20,21 . OLEDs have a coherence length shorter than 2 μm whereas LEDs have a coherence length of ~12 μm 20,21 . Computational methods have shown that beam-width of light sources plays a role in depth of tissue penetration 19 , which means a bigger beam size will result in a higher transmission value.…”

Section: Resultsmentioning

confidence: 99%

Spectral changes associated with transmission of OLED emission through human skin

Yambem

Brooks-Richards

Forrestal

et al. 2019

Sci Rep

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A recent and emerging application of organic light emitting diodes (OLEDs) is in wearable technologies as they are flexible, stretchable and have uniform illumination over a large area. In such applications, transmission of OLED emission through skin is an important part and therefore, understanding spectral changes associated with transmission of OLED emission through human skin is crucial. Here, we report results on transmission of OLED emission through human skin samples for yellow and red emitting OLEDs. We found that the intensity of transmitted light varies depending on the site from where the skin samples are taken. Additionally, we show that the amount of transmitted light reduces by ~ 35–40% when edge emissions from the OLEDs are blocked by a mask exposing only the light emitting area of the OLED. Further, the emission/electroluminescence spectra of the OLEDs widen significantly upon passing through skin and the full width at half maximum increases by >20 nm and >15 nm for yellow and red OLEDs, respectively. For comparison, emission profile and intensities of transmitted light for yellow and red inorganic LEDs are also presented. Our results are highly relevant for the rapidly expanding area of non-invasive wearable technologies that use organic optoelectronic devices for sensing.

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“…Compared to bottom-emitting OLEDs (BEOLEDs), top-emitting OLEDs (TEOLEDs) are more suited to use in display technologies and biomedical applications because they facilitate the use of nontransparent backplane technology for active-matrix OLEDs [ 3 ]. In addition, TEOLEDs offer the advantages of a high aperture ratio and high image quality, which makes them potential candidates for sunlight-readable displays such as smartphones, wrist-worn smartwatches, tablets, and automotive head-up displays [ 4 – 6 ]. However, despite the near 100% IQE of organic emitters, efficient outcoupling remains challenging because a large amount of light is trapped inside various components owing to total internal reflection at interfaces and the surface plasmon losses/absorption of metals [ 7 ].…”

Section: Introductionmentioning

confidence: 99%

Cavity-Suppressing Electrode Integrated with Multi-Quantum Well Emitter: A Universal Approach Toward High-Performance Blue TADF Top Emission OLED

et al. 2022

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A novel device structure for thermally activated delayed fluorescence (TADF) top emission organic light-emitting diodes (TEOLEDs) that improves the viewing angle characteristics and reduces the efficiency roll-off is presented. Furthermore, we describe the design and fabrication of a cavity-suppressing electrode (CSE), Ag (12 nm)/WO3 (65 nm)/Ag (12 nm) that can be used as a transparent cathode. While the TADF-TEOLED fabricated using the CSE exhibits higher external quantum efficiency (EQE) and improved angular dependency than the device fabricated using the microcavity-based Ag electrode, it suffers from low color purity and severe efficiency roll-off. These drawbacks can be reduced by using an optimized multi-quantum well emissive layer (MQW EML). The CSE-based TADF-TEOLED with an MQW EML fabricated herein exhibits a high EQE (18.05%), high color purity (full width at half maximum ~ 59 nm), reduced efficiency roll-off (~ 46% at 1000 cd m−2), and low angular dependence. These improvements can be attributed to the synergistic effect of the CSE and MQW EML. An optimized transparent CSE improves charge injection and light outcoupling with low angular dependence, and the MQW EML effectively confines charges and excitons, thereby improving the color purity and EQE significantly. The proposed approach facilitates the optimization of multiple output characteristics of TEOLEDs for future display applications.

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Measuring and structuring the spatial coherence length of organic light‐emitting diodes

Cited by 12 publications

References 41 publications

Resolving the Spatial Variation and Correlation of Hyperfine Spin Properties in Organic Light‐Emitting Diodes

Resolving the Spatial Variation and Correlation of Hyperfine Spin Properties in Organic Light‐Emitting Diodes

Spectral changes associated with transmission of OLED emission through human skin

Cavity-Suppressing Electrode Integrated with Multi-Quantum Well Emitter: A Universal Approach Toward High-Performance Blue TADF Top Emission OLED

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