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Choi GS, Kang SW, Bae EJ, Jang EB, Baek DH, Ju BK, Park YW. A Simple Method for Fabricating an External Light Extraction Composite Layer with RNS to Improve the Optical Properties of OLEDs. NANOMATERIALS (BASEL, SWITZERLAND) 2022; 12:1430. [PMID: 35564139 PMCID: PMC9103064 DOI: 10.3390/nano12091430] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/27/2022] [Revised: 03/29/2022] [Accepted: 04/20/2022] [Indexed: 02/01/2023]
Abstract
In this study, we fabricated a random nanostructure (RNS) external light extraction composite layer containing high-refractive-index nanoparticles through a simple and inexpensive solution process and a low-temperature mask-free process. We focused on varying the shape and density of the RNSs and adjusted the concentration of the high-refractive-index nanoparticles to control the optical properties. The RNSs fabricated using a low-temperature mask-free process can use the distance between the nanostructures and various forms to control the diffraction and scattering effects in the visible light wavelength range. Consequently, our film exhibited a direct transmittance of ~85% at a wavelength of 550 nm. Furthermore, when the RNSs' composite film, manufactured using the low-temperature mask-free process, was applied to organic light-emitting diodes (OLEDs), it exhibited an external quantum efficiency improvement of 32.2% compared with the OLEDs without the RNSs. Therefore, the randomly distributed high-refractive-index nanoparticles on the polymer film can reduce the waveguide mode and total reflection at the substrate/air interface. These films can be used as a scattering layer to reduce the loss of the OLED substrate mode.
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Affiliation(s)
- Geun-Su Choi
- Nano and Organic-Electronics Laboratory, Department of Display and Semiconductor Engineering, Sun Moon University, Asan 31460, Korea; (G.-S.C.); (S.-W.K.); (E.-J.B.); (E.-B.J.)
| | - Shin-Woo Kang
- Nano and Organic-Electronics Laboratory, Department of Display and Semiconductor Engineering, Sun Moon University, Asan 31460, Korea; (G.-S.C.); (S.-W.K.); (E.-J.B.); (E.-B.J.)
- Display and Nanosystem Laboratory, Department of Electrical Engineering, Korea University, Seoul 02841, Korea
| | - Eun-Jeong Bae
- Nano and Organic-Electronics Laboratory, Department of Display and Semiconductor Engineering, Sun Moon University, Asan 31460, Korea; (G.-S.C.); (S.-W.K.); (E.-J.B.); (E.-B.J.)
- Display and Nanosystem Laboratory, Department of Electrical Engineering, Korea University, Seoul 02841, Korea
| | - Eun-Bi Jang
- Nano and Organic-Electronics Laboratory, Department of Display and Semiconductor Engineering, Sun Moon University, Asan 31460, Korea; (G.-S.C.); (S.-W.K.); (E.-J.B.); (E.-B.J.)
| | - Dong-Hyun Baek
- Center for Next Generation Semiconductor Technology, Department of Display and Semiconductor Engineering, Sun Moon University, Asan 31460, Korea;
| | - Byeong-Kwon Ju
- Display and Nanosystem Laboratory, Department of Electrical Engineering, Korea University, Seoul 02841, Korea
| | - Young-Wook Park
- Nano and Organic-Electronics Laboratory, Department of Display and Semiconductor Engineering, Sun Moon University, Asan 31460, Korea; (G.-S.C.); (S.-W.K.); (E.-J.B.); (E.-B.J.)
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Bae EJ, Kang SW, Choi GS, Jang EB, Baek DH, Ju BK, Park YW. Enhanced Light Extraction from Organic Light-Emitting Diodes with Micro-Nano Hybrid Structure. NANOMATERIALS 2022; 12:nano12081266. [PMID: 35457971 PMCID: PMC9031578 DOI: 10.3390/nano12081266] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/27/2022] [Revised: 03/26/2022] [Accepted: 04/01/2022] [Indexed: 12/10/2022]
Abstract
In this study, an external light extraction layer with a micro-nano hybrid structure was applied to improve the external light extraction efficiency of organic light-emitting diodes (OLEDs). A reactive ion-etching (RIE) process, using O2 and CHF3 plasma, was performed on the surface of the micro-scale pattern to form micro-nano hybrid structures. According to the results of this study, the nanostructures formed by the treatment of O2 and CHF3 were different, and the efficiency according to the structures was analyzed experimentally and theoretically. As a result, the OLED, to which the micro-nano hybrid structure, manufactured through a simple process, is applied, improved the external light extraction efficiency by up to 38%, and an extended viewing angle profile was obtained. Additionally, an effective method for enhancing the out-coupling efficiency of OLEDs was presented by optimizing the micro-nano hybrid structure according to process conditions.
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Affiliation(s)
- Eun-Jeong Bae
- Nano and Organic-Electronics Laboratory, Department of Display and Semiconductor Engineering, Sun Moon University, Asan 31460, Korea; (E.-J.B.); (S.-W.K.); (G.-S.C.); (E.-B.J.)
- Display and Nanosystem Laboratory, Department of Electrical Engineering, Korea University, Seoul 02841, Korea
| | - Shin-Woo Kang
- Nano and Organic-Electronics Laboratory, Department of Display and Semiconductor Engineering, Sun Moon University, Asan 31460, Korea; (E.-J.B.); (S.-W.K.); (G.-S.C.); (E.-B.J.)
- Display and Nanosystem Laboratory, Department of Electrical Engineering, Korea University, Seoul 02841, Korea
| | - Geun-Su Choi
- Nano and Organic-Electronics Laboratory, Department of Display and Semiconductor Engineering, Sun Moon University, Asan 31460, Korea; (E.-J.B.); (S.-W.K.); (G.-S.C.); (E.-B.J.)
| | - Eun-Bi Jang
- Nano and Organic-Electronics Laboratory, Department of Display and Semiconductor Engineering, Sun Moon University, Asan 31460, Korea; (E.-J.B.); (S.-W.K.); (G.-S.C.); (E.-B.J.)
| | - Dong-Hyun Baek
- Center for Next Generation Semiconductor Technology, Department of Display and Semiconductor Engineering, Sun Moon University, Asan 31460, Korea
- Correspondence: (D.-H.B.); (B.-K.J.); (Y.-W.P.)
| | - Byeong-Kwon Ju
- Display and Nanosystem Laboratory, Department of Electrical Engineering, Korea University, Seoul 02841, Korea
- Correspondence: (D.-H.B.); (B.-K.J.); (Y.-W.P.)
| | - Young-Wook Park
- Nano and Organic-Electronics Laboratory, Department of Display and Semiconductor Engineering, Sun Moon University, Asan 31460, Korea; (E.-J.B.); (S.-W.K.); (G.-S.C.); (E.-B.J.)
- Correspondence: (D.-H.B.); (B.-K.J.); (Y.-W.P.)
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Chen G, Weng Y, Lai X, Wang W, Zhou X, Yan Q, Guo T, Zhang Y, Wu C. Design and fabrication of hybrid MLAs/gratings for the enhancement of light extraction efficiency and distribution uniformity of OLEDs. OPTICS EXPRESS 2021; 29:25812-25823. [PMID: 34614901 DOI: 10.1364/oe.427258] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/09/2021] [Accepted: 07/21/2021] [Indexed: 06/13/2023]
Abstract
Extracting light from organic light-emitting diodes (OLEDs) and improving the angular distribution are essential for their commercial applications in illumination and displays. In this work, hybrid microlens arrays (MLAs) and gratings with periods and depths in the scale of submicron have been designed and incorporated on the lighting surface of OLEDs for simultaneous enhancement of light outcoupling efficiency and angular distribution improvement. It is found that the augmentation of light extraction efficiency is mainly attributed to the MLAs, while the gratings can improve the viewing angle by increasing the angular distribution uniformity. A novel approach was proposed by combining photoresist thermal reflow, soft-lithography and plasma treatments on polydimethylsiloxane (PDMS) surfaces synergistically to realize gratings on the wavy surface of MLAs. It has been proved that with the hybrid MLAs/gratings, the external quantum efficiency (EQE) of the OLED can reach up to 22.8%, which increased by 24% compared to that of bare OLED. Moreover, the OLED with the hybrid MLAs/gratings showed an obvious lateral enhancement at wider viewing angle.
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Shin CH, Huseynova G, Kim E, Lee J, Yoo S, Choi Y, Lee JH. Random Al 2O 3 nanoparticle-based polymer composite films as outcoupling layers for flexible organic light-emitting diodes. OPTICS EXPRESS 2020; 28:26170-26179. [PMID: 32906893 DOI: 10.1364/oe.400687] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/24/2020] [Accepted: 08/07/2020] [Indexed: 06/11/2023]
Abstract
Random Al2O3 nanoparticle-based polymer composite films are investigated as external scattering layers to enhance light extraction from flexible organic light-emitting diodes (OLEDs). We found that the size and concentration of the nanoparticles (NPs) in the polymer film play a crucial role in improving light extraction. It turned out that their increase has a favorable impact on the light output of the devices, as the high concentration of the NPs leads to the formation of large nanoparticle clusters, which, in turn, yield pore-containing films. As a result, light extraction efficiency of the flexible OLEDs on PEN substrates was enhanced by a factor of 1.65 by the incorporation of the scattering layer, with the highest Al2O3 NP concentration of 99 wt%. This outcome is attributed to the reduction of the waveguide mode and total internal reflection at the substrate/air interface induced by the randomly distributed NPs in the flexible scattering layer. Our work demonstrates an efficient, solution-processable, and low-cost light-outcoupling structure for large-area and flexible OLED applications.
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Son I, Lee JH. Highly Transparent and Wide Viewing Optical Films Using Embedded Hierarchical Double-Shell Layered Nanoparticles with Gradient Refractive Index Surface. ACS APPLIED MATERIALS & INTERFACES 2020; 12:30862-30870. [PMID: 32539333 DOI: 10.1021/acsami.0c08730] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
The essential improvements in the performance of light-diffusing materials for wide viewing angles in potential optoelectronic applications have attracted considerable attention. In this study, a simple and unprecedented strategy is proposed to simultaneously provide exceptional light scattering performance and high optical transparency for transparent optical thin films using hierarchical double-shell nanoparticles possessing a refractive index gradient on the nanoparticle surface. The hierarchical SiO2/TiO2/poly(methyl methacrylate) (PMMA) double-shell layered nanoparticles induce enhanced light scattering properties by their nanolayered gradient refractive index structure. Fourier transform infrared spectroscopy and scanning electron microscopy-energy-dispersive X-ray spectroscopy analyses show the successful formation of the multiple nanolayered structure of the double-shell nanoparticles. The synthesized SiO2/TiO2/PMMA nanoparticles with a diameter of 40 nm and a TiO2 layer thickness of 4.5 nm exhibit the highest diffuse reflectance of 87% in the visible region. An ultraviolet-light-cured optical film with an extremely low content of double-shell nanoparticles exhibits efficient light scattering characteristics while maintaining high optical transparency. This study provides a facile yet effective, scalable approach to improve the viewing angle performances of optoelectronic devices and paves the new way for further studies on the wide applications of light scattering phenomenon using optically active hierarchical nanoparticles with multiple refractive indices.
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Affiliation(s)
- Intae Son
- Center for Coating Materials and Processing, Seoul National University, Seoul 08826, Korea
| | - Jun Hyup Lee
- Department of Chemical Engineering, Soongsil University, Seoul 06978, Korea
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Lee DJ, Yoon IS, Park CH, Choi J, Park YW, Ju BK. Extraction of Light Using Random Nanocone on Poly(vinyl-butyral) for Flexible OLEDs. Sci Rep 2019; 9:12312. [PMID: 31444381 PMCID: PMC6707228 DOI: 10.1038/s41598-019-48808-8] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2018] [Accepted: 07/30/2019] [Indexed: 12/04/2022] Open
Abstract
In this study, we designed a smooth, highly flexible, mechanically robust poly(vinyl-butyral) (PVB)/silver nanowire (AgNW) composite transparent conducting electrode (TCE) integrated with a random nanocone (RNC) to enhance the light extraction of flexible organic light-emitting diodes (OLEDs). The RNC was fabricated by reactive-ion etching (RIE) on AgNW embedded in PVB. As the etching time increased, the size of the RNC became larger. The sheet resistance and transmittance of PVB/AgNW with the RNC was 21.7 Ω/sq and ~87%, respectively. For the PVB/AgNW, the change in sheet resistance was only 2.6% when a 2,000-bend test was performed. The maximum external quantum efficiency was 28.3% when RNC 700 s was used as a green phosphorescent OLED. In addition, for current efficiency and power efficiency, RNC 700 s increased 1.4 times over RNC 0 s. RNC is free of viewing-angle-dependent color and brightness distortion. PVB/AgNW and RNC are practical ways to overcome the brittleness of conventional indium tin oxide and improve the efficiency of flexible OLEDs. Finally, this product is expected to be applied to various flexible optical devices.
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Affiliation(s)
- Dong Jun Lee
- Display and Nanosystem Laboratory, Department of Electrical Engineering, Korea University, 145, Anam-ro, Seongbuk-gu, Seoul, 02841, Republic of Korea
| | - In Seon Yoon
- Display and Nanosystem Laboratory, Department of Electrical Engineering, Korea University, 145, Anam-ro, Seongbuk-gu, Seoul, 02841, Republic of Korea
| | - Cheol Hwee Park
- Display and Nanosystem Laboratory, Department of Electrical Engineering, Korea University, 145, Anam-ro, Seongbuk-gu, Seoul, 02841, Republic of Korea
| | - Junhee Choi
- Display and Nanosystem Laboratory, Department of Electrical Engineering, Korea University, 145, Anam-ro, Seongbuk-gu, Seoul, 02841, Republic of Korea
| | - Young Wook Park
- School of Mechanical and ICT Convergence Engineering, SUN MOON University, 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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