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Jeong JC, Woo KY, Cho H, Cho YH, Cho NS, Yang SY, Moon J. Extracting internal modes of top emission organic light emitting diodes by using internal random mesoscopic wrinkles. J IND ENG CHEM 2021. [DOI: 10.1016/j.jiec.2021.01.025] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Park CH, Kang SW, Jung SG, Lee DJ, Park YW, Ju BK. Enhanced light extraction efficiency and viewing angle characteristics of microcavity OLEDs by using a diffusion layer. Sci Rep 2021; 11:3430. [PMID: 33564021 PMCID: PMC7873264 DOI: 10.1038/s41598-021-82753-9] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2020] [Accepted: 01/19/2021] [Indexed: 11/20/2022] Open
Abstract
The viewing angle characteristics and light extraction efficiency of organic light-emitting diodes (OLEDs) with a micro-cavity structure were enhanced. This was accomplished by inserting a diffusion layer composed of nano-sized structures of a transparent polymer poly(methyl methacrylate) (PMMA) combined with a zinc oxide (ZnO) semi-planarization layer with a high refractive index (n = 2.1) into the devices. The PMMA nanostructures were fabricated by employing a reactive ion etching (RIE) process. The height and density of the PMMA nanostructures were controlled by varying the speed at which the PMMA was spin-coated onto the substrate. The insertion of the diffusion layer into the micro-cavity OLEDs (MC-OLEDs) improved the external quantum efficiency (EQE) by as much as 17% when compared to that of a MC-OLED without a diffusion layer. Furthermore, adjustment of the viewing angle from 0° to 60° halved the peak shift distance of the electroluminescence (EL) spectra from 42 to 20 nm. Additionally, changing the viewing angle from 0° to 60° changed the color coordinate movement distance of the MC-OLED with the diffusion layer to 0.078, less than half of the distance of the MC-OLED without the diffusion layer (0.165).
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Affiliation(s)
- Cheol Hwee Park
- Display and Nanosystem Laboratory, Department of Electrical Engineering, Korea University, 145, Anam-ro, Seongbuk-gu, Seoul, 02841, Republic of Korea
| | - Shin Woo Kang
- Display and Nanosystem Laboratory, Department of Electrical Engineering, Korea University, 145, Anam-ro, Seongbuk-gu, Seoul, 02841, Republic of Korea.,Nano and Organic-Electronics Laboratory, Department of Display and Semiconductor Engineering, Sun Moon University, Asan, Chungcheongnam-do, 31460, Republic of Korea
| | - Sun-Gyu Jung
- Display and Nanosystem Laboratory, Department of Electrical Engineering, Korea University, 145, Anam-ro, Seongbuk-gu, Seoul, 02841, Republic of Korea
| | - Dong Jun Lee
- Display and Nanosystem Laboratory, Department of Electrical Engineering, Korea University, 145, Anam-ro, Seongbuk-gu, Seoul, 02841, Republic of Korea
| | - Young Wook Park
- Nano and Organic-Electronics Laboratory, Department of Display and Semiconductor Engineering, Sun Moon University, Asan, Chungcheongnam-do, 31460, Republic of Korea.
| | - Byeong-Kwon Ju
- Display and Nanosystem Laboratory, Department of Electrical Engineering, Korea University, 145, Anam-ro, Seongbuk-gu, Seoul, 02841, Republic of Korea.
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Zhang YB, Ou QD, Li YQ, Chen JD, Zhao XD, Wei J, Xie ZZ, Tang JX. Transparent organic light-emitting diodes with balanced white emission by minimizing waveguide and surface plasmonic loss. OPTICS EXPRESS 2017; 25:15662-15675. [PMID: 28789080 DOI: 10.1364/oe.25.015662] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/02/2017] [Accepted: 06/14/2017] [Indexed: 06/07/2023]
Abstract
It is challenging in realizing high-performance transparent organic light-emitting diodes (OLEDs) with symmetrical light emission to both sides. Herein, an efficient transparent OLED with highly balanced white emission to both sides is demonstrated by integrating quasi-periodic nanostructures into the organic emitter and the metal-dielectric composite top electrode, which can simultaneously suppressing waveguide and surface plasmonic loss. The power efficiency and external quantum efficiency are raised to 83.5 lm W-1 and 38.8%, respectively, along with a bi-directional luminance ratio of 1.26. The proposed scheme provides a facile route for extending application scope of transparent OLEDs for future transparent displays and lightings.
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Gim S, Lee I, Park JY, Lee JL. Spontaneously Embedded Scattering Structures in a Flexible Substrate for Light Extraction. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2017; 13:1604168. [PMID: 28464506 DOI: 10.1002/smll.201604168] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/16/2016] [Revised: 03/09/2017] [Indexed: 06/07/2023]
Abstract
A flexible hazy substrate (FHS) with embedded air bubbles to increase light extraction efficiency of organic light-emitting diodes (OLEDs) is reported. In order to embed the air bubbles in the flexible substrate, micropatterned substrates are fabricated by plasma treatment, and then coated with a planarization layer. During the planarization layer coating, air bubbles are trapped between the substrate and the planarization layer. The haze of the FHS can be controlled from 1.7% to 68.4% by changing the size of micropatterns by adjusting the plasma treatment time. The FHS shows average haze of 68.4%, average total transmittance of 90.3%, and extremely flat surface with average roughness (R a ) of 1.2 nm. Rigorous coupled-wave analysis and finite-difference time-domain simulations are conducted to demonstrate that the air bubbles in the substrate can effectively extract photons that are trapped in the substrate. The FHS increases the power efficiency of OLEDs by 22% and further increases by 91% combined with an external extraction layer. Moreover, the FHS has excellent mechanical flexibility. No defect has been observed after 10 000 bending cycles at bending radius of 4 mm.
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Affiliation(s)
- Seungo Gim
- Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Gyeongbuk-do, Pohang-si, 37673, Republic of Korea
| | - Illhwan Lee
- Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Gyeongbuk-do, Pohang-si, 37673, Republic of Korea
| | - Jae Yong Park
- Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Gyeongbuk-do, Pohang-si, 37673, Republic of Korea
| | - Jong-Lam Lee
- Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Gyeongbuk-do, Pohang-si, 37673, Republic of Korea
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Park YS, Han KH, Kim J, Cho DH, Lee J, Han Y, Lim JT, Cho NS, Yu B, Lee JI, Kim JJ. Crystallization-assisted nano-lens array fabrication for highly efficient and color stable organic light emitting diodes. NANOSCALE 2017; 9:230-236. [PMID: 27906406 DOI: 10.1039/c6nr07798f] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
To date, all deposition equipment has been developed to produce planar films. Thus lens arrays with a lens diameter of <1 mm have been manufactured by combining deposition with other technologies, such as masks, surface treatment, molding etc. Furthermore, a nano-lens array (NLA) with a sufficiently small lens diameter (<1 μm) is necessary to avoid image quality degradation in high resolution displays. In this study, an organic NLA made using a conventional deposition technique - without combining with other techniques - is reported. Very interestingly, grazing-incidence small-angle X-ray scattering (GI-SAXS) experiments indicate that the NLA is formed by the crystallization of organic molecules and the resulting increase in surface tension. The lens diameter can be tuned for use with any kind of light by controlling the process parameters. As an example of their potential applications, we use NLAs as a light extraction film for organic light emitting diodes (OLEDs). The NLA is integrated by directly depositing it on the top electrode of a collection of OLEDs. This is a dry process, meaning that it is fully compatible with the current OLED production process. Devices with NLAs exhibited a light extraction efficiency 1.5 times higher than devices without, which corresponds well with simulation results. The simulations show that this high efficiency is due to the reduction of the guided modes by scattering at the NLA. The NLAs also reduce image blurring, indicating that they increase color stability.
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Affiliation(s)
- Young-Sam Park
- Flexible Information Device Research Section, Electronics and Telecommunications Research Institute (ETRI), Daejeon, 34129, Republic of Korea.
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Bi YG, Feng J, Ji JH, Chen Y, Liu YS, Li YF, Liu YF, Zhang XL, Sun HB. Ultrathin and ultrasmooth Au films as transparent electrodes in ITO-free organic light-emitting devices. NANOSCALE 2016; 8:10010-5. [PMID: 27128168 DOI: 10.1039/c6nr00599c] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
An ultrathin, ultrasmooth and flexible Au film as an alternative of the indium-tin oxide (ITO) electrode in organic light-emitting devices (OLEDs) has been reported. The 7 nm Au film shows excellent surface morphology, optical and electronic characteristics including a root-mean-square roughness of 0.35 nm, a high transparency of 72% at 550 nm, and a sheet resistance of 23.75 Ω sq(-1). These features arise from the surface modification of the glass substrate by using a SU-8 film, which fixes metal atoms via chemical bond interactions between Au and SU-8 film to suppress the island growth mode. A 17% enhancement in current efficiency has been obtained from the OLEDs based on the ultrathin Au electrodes compared to that of the devices with the ITO electrodes. The OLEDs with the ultrathin Au/SU-8 anodes exhibit high flexibility and mechanical robustness.
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Affiliation(s)
- Yan-Gang Bi
- State Key Laboratory on Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, 2699 Qianjin Street, Changchun, 130012, People's Republic of China.
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Shim YS, Hwang JH, Park CH, Jung SG, Park YW, Ju BK. An extremely low-index photonic crystal layer for enhanced light extraction from organic light-emitting diodes. NANOSCALE 2016; 8:4113-4120. [PMID: 26822966 DOI: 10.1039/c5nr07312j] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
This paper reports organic light-emitting diodes (OLEDs) with improved light extraction fabricated by embedding an extremely low-index photonic crystal (LIPC) layer. The LIPC layer increases the optical efficiency through the reduced wave-guide mode between the substrate and anode both by increased light resonance and by a strengthened diffraction effect from an extremely low-refractive-index medium, specifically a line structure composed of a vacuum gap. As a result, the current efficiency and power efficiency of the LIPC-OLEDs are 1.51 and 1.93 times higher, respectively, than the reference device at 1000 cd m(-2). Because most of the light extraction is significant, especially in the forward direction, at the specific wavelengths satisfying the Bragg's diffraction equation, it is possible to calculate the anomalous spectrum of the LIPC-OLED through the finite-difference time domain (FDTD) method.
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Affiliation(s)
- Yong Sub Shim
- Display and Nanosystem Laboratory, College of Engineering, Korea University, Seoul 136-713, Republic of Korea.
| | - Ju Hyun Hwang
- Display and Nanosystem Laboratory, College of Engineering, Korea University, Seoul 136-713, Republic of Korea.
| | - Cheol Hwee Park
- Display and Nanosystem Laboratory, College of Engineering, Korea University, Seoul 136-713, Republic of Korea.
| | - Sun-Gyu Jung
- Display and Nanosystem Laboratory, College of Engineering, Korea University, Seoul 136-713, Republic of Korea.
| | - Young Wook Park
- The Institute of High Technology Materials and Devices, Korea University, Seoul 136-713, Republic of Korea.
| | - Byeong-Kwon Ju
- Display and Nanosystem Laboratory, College of Engineering, Korea University, Seoul 136-713, Republic of Korea.
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Lee K, Lee J, Kim E, Lee JI, Cho DH, Lim JT, Joo CW, Kim JY, Yoo S, Ju BK, Moon J. Simultaneously enhanced device efficiency, stabilized chromaticity of organic light emitting diodes with lambertian emission characteristic by random convex lenses. NANOTECHNOLOGY 2016; 27:075202. [PMID: 26778539 DOI: 10.1088/0957-4484/27/7/075202] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
An optical functional film applicable to various lighting devices is demonstrated in this study. The phase separation of two immiscible polymers in a common solvent was used to fabricate the film. In this paper, a self-organized lens-like structure is realized in this manner with optical OLED functional film. For an OLED, there are a few optical drawbacks, including light confinement or viewing angle distortion. By applying the optical film to an OLED, the angular spectra distortion resulting from the designed organic stack which produced the highest efficiency was successfully stabilized, simultaneously enhancing the efficiency of the OLED. We prove the effect of the film on the efficiency of OLEDs through an optical simulation. With the capability to overcome the main drawbacks of OLEDs, we contend that the proposed film can be applied to various lighting devices.
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Affiliation(s)
- Keunsoo Lee
- Soft I/O Interface Research Section, Electronics and Telecommunications Research Institute (ETRI), Daejeon 34129, Korea
- Display and Nanosystem Laboratory, College of Engineering, Korea University, Seoul 02842, Korea
| | - Jonghee Lee
- Soft I/O Interface Research Section, Electronics and Telecommunications Research Institute (ETRI), Daejeon 34129, Korea
| | - Eunhye Kim
- Department of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST) Daejeon 34141, Korea
| | - Jeong-Ik Lee
- Soft I/O Interface Research Section, Electronics and Telecommunications Research Institute (ETRI), Daejeon 34129, Korea
| | - Doo-Hee Cho
- Soft I/O Interface Research Section, Electronics and Telecommunications Research Institute (ETRI), Daejeon 34129, Korea
| | - Jong Tae Lim
- Soft I/O Interface Research Section, Electronics and Telecommunications Research Institute (ETRI), Daejeon 34129, Korea
| | - Chul Woong Joo
- Soft I/O Interface Research Section, Electronics and Telecommunications Research Institute (ETRI), Daejeon 34129, Korea
| | - Joo Yeon Kim
- Soft I/O Interface Research Section, Electronics and Telecommunications Research Institute (ETRI), Daejeon 34129, Korea
| | - Seunghyup Yoo
- Department of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST) Daejeon 34141, Korea
| | - Byeong-Kwon Ju
- Display and Nanosystem Laboratory, College of Engineering, Korea University, Seoul 02842, Korea
| | - Jaehyun Moon
- Soft I/O Interface Research Section, Electronics and Telecommunications Research Institute (ETRI), Daejeon 34129, Korea
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Chung J, Cho H, Koh TW, Lee J, Kim E, Lee J, Lee JI, Yoo S. Towards highly efficient and highly transparent OLEDs: advanced considerations for emission zone coupled with capping layer design. OPTICS EXPRESS 2015; 23:27306-27314. [PMID: 26480391 DOI: 10.1364/oe.23.027306] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Strategies to achieve efficient transparent organic light-emitting diodes (TrOLEDs) are presented. The emission zone position is carefully adjusted by monitoring the optical phase change upon reflection from the top electrode, which is significant when the thickness of the capping layer changes. With the proposed design strategy, external quantum efficiency and transmittance values as high as 15% and 80% are demonstrated simultaneously. The effect of surface plasmon polariton (SPP) loss from thin metal electrodes is also taken into account to correctly describe the full scaling behavior of the efficiency of TrOLEDs over key optical design parameters.
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