Enhanced out-coupling factor of microcavity organic light-emitting devices with irregular microlens array

Lim, Jongsun; Oh, Seung Seok; Kim, Doo Youp; Cho, Sang‐Hee; Kim, In Tae; Han, Sang Heon; Takezoe, Hideo; Choi, Eun Ha; Cho, Guang Sup; Seo, Young Hun; Kang, Seung Oun; Park, Byoungchoo

doi:10.1364/oe.14.006564

Cited by 71 publications

(39 citation statements)

References 20 publications

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“…3,4 Another possibility to increase the light out coupling is lenses on the surface of OLEDs. [5][6][7][8][9][10][11][12] Hollow spheres embedded in the layers 13 or glass substrates blast with sand 14 are other possibilities for scattering the light. However, these methods are very time-consuming or very costly.…”

Section: Introductionmentioning

confidence: 99%

Development and characterization of adjustable refractive index scattering epoxy acrylate polymer layers

Eiselt

Preinfalk

Gleißner³

et al. 2016

SPIE Proceedings

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Abstract. Several polymer films for improved optical properties in optoelectronic devices are presented. In such optical applications, it is sometimes important to have a film with an adjusted refractive index, scattering properties, and a low surface roughness. These diffusing films can be used to increase the efficiency of optoelectronic components, such as organic light-emitting diodes. Three different epoxy acrylate mixtures containing Syntholux 291 EA, bisphenol A glycerolate dimethacrylate, and Sartomer SR 348 L are characterized and optimized with different additives. The adjustable refractive index of the material is achieved by chemical doping using 9-vinylcarbazole. Titanium nanoparticles in the mixtures generate light scattering and increase the refractive index additionally. A high-power stirrer is used to mix and disperse all chemical substances together to a homogenous mixture. The viscosity behavior of the mixtures is an important property for the selection of the production method and, therefore, the viscosity measurement results are presented. After the mixing, the monomer mixture is applied on glass substrates by screen printing. To initiate polymerization, the produced films are irradiated for 10 min with ultraviolet radiation and heat. Transmission measurements of the polymer matrix and roughness measurements complement the characterization.

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Section: Introductionmentioning

confidence: 99%

Development and characterization of adjustable refractive index scattering epoxy acrylate polymer layers

Eiselt

Preinfalk

Gleißner³

et al. 2016

SPIE Proceedings

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“…The majority of light is either reabsorbed by the materials or leaks out from the device edges where photon recapturing for useful emission has proven problematic. The use of microlens arrays (μLAs) is a notable approach to overcome the foregoing outcoupling limits [2][3][4][5][6][7][8][9][10][11]. However, fabrication of such arrays is either not economical or the resulting outcoupling enhancement is reported to be < 80%, especially if the array is either confined to an area directly under the pixel [2][3][4][5]7] or that area under the pixel is excluded [8].…”

Section: Introductionmentioning

confidence: 99%

Soft holographic interference lithography microlens for enhanced organic light emitting diode light extraction

Park¹,

Gan²,

Leung³

et al. 2011

Opt. Express

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Very uniform 2 μm-pitch square microlens arrays (μLAs), embossed on the blank glass side of an indium-tinoxide (ITO)-coated 1.1 mm-thick glass, are used to enhance light extraction from organic light-emitting diodes (OLEDs) by ~100%, significantly higher than enhancements reported previously. The array design and size relative to the OLED pixel size appear to be responsible for this enhancement. The arrays are fabricated by very economical soft lithography imprinting of a polydimethylsiloxane (PDMS) mold (itself obtained from a Ni master stamp that is generated from holographic interference lithography of a photoresist) on a UV-curable polyurethane drop placed on the glass. Green and blue OLEDs are then fabricated on the ITO to complete the device. When the μLA is ~15 × 15 mm 2 , i.e., much larger than the ~3 × 3 mm 2 OLED pixel, the electroluminescence (EL) in the forward direction is enhanced by ~100%. Similarly, a 19 × 25 mm 2 μLA enhances the EL extracted from a 3 × 3 array of 2 × 2 mm 2 OLED pixels by 96%. Simulations that include the effects of absorption in the organic and ITO layers are in accordance with the experimental results and indicate that a thinner 0.7 mm thick glass would yield a ~140% enhancement. Abstract: Very uniform 2 μm-pitch square microlens arrays (μLAs), embossed on the blank glass side of an indium-tin-oxide (ITO)-coated 1.1 mm-thick glass, are used to enhance light extraction from organic lightemitting diodes (OLEDs) by ~100%, significantly higher than enhancements reported previously. The array design and size relative to the OLED pixel size appear to be responsible for this enhancement. The arrays are fabricated by very economical soft lithography imprinting of a polydimethylsiloxane (PDMS) mold (itself obtained from a Ni master stamp that is generated from holographic interference lithography of a photoresist) on a UV-curable polyurethane drop placed on the glass. Green and blue OLEDs are then fabricated on the ITO to complete the device. When the μLA is ~15 × 15 mm 2 , i.e., much larger than the ~3 × 3 mm 2 OLED pixel, the electroluminescence (EL) in the forward direction is enhanced by ~100%. Similarly, a 19 × 25 mm 2 μLA enhances the EL extracted from a 3 × 3 array of 2 × 2 mm 2 OLED pixels by 96%. Simulations that include the effects of absorption in the organic and ITO layers are in accordance with the experimental results and indicate that a thinner 0.7 mm thick glass would yield a ~140% enhancement. Keywords

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“…Various approaches for enhancing the optical outcoupling efficiency of bottom emitting OLEDs have been introduced in the literature. Often, the planar substrate/air interface is modified in order to reduce repeated TIR: by using a microlens array [2][3][4] or a large half sphere lens [5] on the substrate surface. Other outcoupling methods try to extract the light trapped in the organic/ITO layers.…”

Section: Introductionmentioning

confidence: 99%

Exceptionally efficient organic light emitting devices using high refractive index substrates

Mladenovski

Neyts

Pavicic³

et al. 2009

Opt. Express

106

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Organic light emitting devices (OLEDs) are now used in commercial cell phones and flat screen displays, but may become even more successful in lighting applications, in which large area, high efficiency, long lifetime and low cost are essential. Due to the relatively high refractive index of the organic layers, conventional planar bottom emitting OLEDs have a low outcoupling efficiency. Various approaches for enhancing the optical outcoupling efficiency of bottom emitting OLEDs have been introduced in the literature. In this paper we demonstrate a green bottom emitting OLED with a record external quantum efficiency (42%) and luminous efficacy (183 lm/W). This OLED is based on a high index substrate and a thick electron transport layer (ETL) which uses electrical doping. The efficient light outcoupling is modeled by optical simulations. 3779-3781 (2003). 10. Y. Sun, and S. R. Forrest, "Enhanced light out-coupling of organic light-emitting devices using embedded lowindex grids," Nat. Photonics 2(8), 483-487 (2008). 11. T. Nakamura, N. Tsutsumi, N. Juni, and H. Fujii, "Thin-film waveguiding mode light extraction in organic electroluminescent device using high refractive index substrate," J. Appl. Phys. 97(5), 054505 (2005). 12. ©2009 Optical Society of America

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Enhanced out-coupling factor of microcavity organic light-emitting devices with irregular microlens array

Cited by 71 publications

References 20 publications

Development and characterization of adjustable refractive index scattering epoxy acrylate polymer layers

Development and characterization of adjustable refractive index scattering epoxy acrylate polymer layers

Soft holographic interference lithography microlens for enhanced organic light emitting diode light extraction

Exceptionally efficient organic light emitting devices using high refractive index substrates

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