Suppression of roll-off characteristics of organic light-emitting diodes by narrowing current injection/transport area to 50 nm

Hayashi, Kyohei; Nakanotani, Hajime; Inoue, Makoto; Yoshida, Kou; Mikhnenko, Oleksandr V.; Nguyen, Thuc Quyen; Adachi, Chihaya

doi:10.1063/1.4913461

Cited by 53 publications

(46 citation statements)

References 35 publications

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“…It has recently been shown experimentally that OLEDs with 50 nm diameter electrodes retain higher external quantum efficiency at large current densities than larger OLEDs and that current densities (40-fold improvement in critical current density for EQE roll-off). 285,286 However, we like to point out that for realizing electrically pumped organic lasers, the dimensions of the OLED should probably not be smaller than the lateral extension of the mode supported by the structure (characteristics size, > λ/2) as this would lead to a small overlap between the laser mode and the pumped region of the device which will lead to reduced modal gain.…”

Section: Increasing Charge Carrier Mobility and Reducing Excitonic Anmentioning

confidence: 99%

Organic Lasers: Recent Developments on Materials, Device Geometries, and Fabrication Techniques

2016

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Organic dyes have been used as gain medium for lasers since the 1960s, long before the advent of today's organic electronic devices. Organic gain materials are highly attractive for lasing due to their chemical tunability and large stimulated emission cross section. While the traditional dye laser has been largely replaced by solid-state lasers, a number of new and miniaturized organic lasers have emerged that hold great potential for lab-on-chip applications, biointegration, low-cost sensing and related areas, which benefit from the unique properties of organic gain materials. On the fundamental level, these include high exciton binding energy, low refractive index (compared to inorganic semiconductors), and ease of spectral and chemical tuning. On a technological level, mechanical flexibility and compatibility with simple processing techniques such as printing, roll-to-roll, self-assembly, and soft-lithography are most relevant. Here, the authors provide a comprehensive review of the developments in the field over the past decade, discussing recent advances in organic gain materials, which are today often based on solid-state organic semiconductors, as well as optical feedback structures, and device fabrication. Recent efforts toward continuous wave operation and electrical pumping of solid-state organic lasers are reviewed, and new device concepts and emerging applications are summarized.

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Section: Increasing Charge Carrier Mobility and Reducing Excitonic Anmentioning

confidence: 99%

Organic Lasers: Recent Developments on Materials, Device Geometries, and Fabrication Techniques

2016

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“…Note that the exact determination of the n-PLED turn-on voltage may be limited by the specific detectivity of the photodetector used under the measurement conditions (the dark current, I D , measured in our experimental setup was in the range of 100 pA, which is 10 times higher than the nominal I D =10 pA given by the manufacturer). The device area of 160 μm 2 (calculated from electrode height (40 nm), multiplied by its width (4 mm)) and high current allow for current densities around 875 kA m −2 to be calculated at 10 V which is far higher than values reported for sandwich device structures (usually 10 3 -10 4 A m −2 ) and could be of interest for organic semiconductor laser diode applications [6]. We do note, however, that this rather high current density is expected to be overestimated due to the non-ideal device geometry and the resulting current spreading over the surface of the nanogap electrodes due to the larger thickness of the organic active layer.…”

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confidence: 96%

“…From an operational standpoint, miniaturised light-emitting diodes are advantageous to larger area ones, as higher current densities can be sustained thanks to efficient dissipation of Joule heating [4,5]. Indeed a suppression of organic light-emitting diodes (OLEDs) rolloff characteristics has been observed upon narrowing the current injection/transport area down to 50 nm [6]. These developments led to demonstration of low threshold amplified spontaneous emission in light-emitting polymer films [7], which could pave the way to the realisation of electrically pumped organic lasers [8].…”

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confidence: 99%

Flexible nanogap polymer light-emitting diodes fabricated via adhesion lithography (a-Lith)

et al. 2018

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We report the development of coplanar green colour organic light-emitting diodes (OLEDs) based on asymmetric nanogap electrodes fabricated on different substrates including glass and plastic. Using adhesion lithography (a-Lith) we pattern Al and Au layers acting as the cathode and anode electrodes, respectively, separated by an inter-electrode distance of <15 nm with an aspect ratio of up to 10 6 . Spin-coating the organic light-emitting polymer poly(9,9-dioctylfluorene-alt-bithiophene) (F8T2) on top of the asymmetric Al-Au nanogap electrodes results in green light-emitting nanogap OLEDs with promising operating characteristics. We show that the scaling of the OLED's width from 4 to 200 mm can substantially improve the light output of the device without any adverse effects on the manufacturing yield. Furthermore, it is found that the light-emitting properties in the nanogap area differ from the bulk organic film, an effect attributed to confinement of the conjugated polymer chains in the nanogap channel. These results render a-Lith particularly attractive for low cost facile fabrication of nanoscale light-emitting sources and arrays on different substrates of arbitrary size.Nanometer-sized polymer light-emitting diodes (n-PLEDs) have been proposed as light sources in subwavelength scanning near-field optical microscopes as well as in nanoscale photo-patterning to create simultaneously a large number of identical patterns [1,2]. Their unique advantages are colour tunability, versatility in geometrical pattern selection and ease of manufacturing of nanostructured arrays using low cost solution processing on substrates of arbitrary size and shape [3]. From an operational standpoint, miniaturised light-emitting diodes are advantageous to larger area ones, as higher current densities can be sustained thanks to efficient dissipation of Joule heating [4,5]. Indeed a suppression of organic light-emitting diodes (OLEDs) rolloff characteristics has been observed upon narrowing the current injection/transport area down to 50 nm [6]. These developments led to demonstration of low threshold amplified spontaneous emission in light-emitting polymer films [7], which could pave the way to the realisation of electrically pumped organic lasers [8]. Further progress has, however, been hindered by manufacturing challenges, as shadow masking and conventional photolithography cannot produce nanometer-sized electrode feature between different metals, and e-beam lithography is not suitable for upscale while it is often limited to a single electrode material. We have recently introduced adhesion lithography (a-Lith) technique as a viable alternative for the scalable sub-15 nm patterning of asymmetric, i.e. of different work function, coplanar metal electrodes on large area flexible substrates [9]. The asymmetric nature of the electrodes, which is difficult to obtain with other common nanopatterning techniques, allows for a range of electronic nanogap devices to be created via simply depositing a single layer of active material on top of d...

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“…Joule heating and subsequent degradation may also be an issue, even though many applications do not require continuous operation at high luminance . Several studies have reported that under pulsed operation conditions and through use of a small active area, OLEDs can sustain dramatically increased current densities . Additionally, choosing a substrate with high thermal conductivity improves heat dissipation and thus prevents potential thermal breakdown .…”

Section: Introductionmentioning

confidence: 99%

Development of Very High Luminance p–i–n Junction‐Based Blue Fluorescent Organic Light‐Emitting Diodes

Deng

Murawski

Keum

et al. 2020

Advanced Optical Materials

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Organic light‐emitting diodes (OLEDs) can emit light over much larger areas than their inorganic counterparts, offer mechanical flexibility, and can be readily integrated on various substrates and backplanes. However, the amount of light they emit per unit area is typically lower and the required operating voltage is higher, which can be a limitation for emerging applications of OLEDs, e.g., in outdoor and high‐dynamic‐range displays, biomedical devices, or visible‐light communication. Here, high‐luminance, blue‐emitting (λpeak = 464 nm), fluorescent p–i–n OLEDs are developed by combining three strategies: First, the thickness of the intrinsic layers in the device is decreased to reduce internal voltage loss. Second, different electron‐blocking layer materials are tested to recover efficiency losses resulting from this thickness reduction. Third, the geometry of the anode contact is optimized, which leads to a substantial reduction in the in‐plane resistive voltage losses. The OLEDs retain a maximum external quantum efficiency of 4.4% as expected for an optimized fluorescent device and reach a luminance of 132 000 cd m−2 and an optical power density of 2.4 mW mm−2 at 5 V, a nearly eightfold improvement compared to the original reference device.

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Suppression of roll-off characteristics of organic light-emitting diodes by narrowing current injection/transport area to 50 nm

Cited by 53 publications

References 35 publications

Organic Lasers: Recent Developments on Materials, Device Geometries, and Fabrication Techniques

Organic Lasers: Recent Developments on Materials, Device Geometries, and Fabrication Techniques

Flexible nanogap polymer light-emitting diodes fabricated via adhesion lithography (a-Lith)

Development of Very High Luminance p–i–n Junction‐Based Blue Fluorescent Organic Light‐Emitting Diodes

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