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Lim S, Ahn HS, Jang EJ, Boo SY, Gasonoo A, Gwag JS, Lee JH, Choi Y. Polymer Dispersed Liquid Crystal Imprinted by Microlens Array for Enhanced Outcoupling Efficiency of Organic Light Emitting Diode. Molecules 2023; 29:73. [PMID: 38202660 PMCID: PMC10779693 DOI: 10.3390/molecules29010073] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2023] [Revised: 12/19/2023] [Accepted: 12/20/2023] [Indexed: 01/12/2024] Open
Abstract
In this paper, we demonstrate the use of polymer dispersed liquid crystal (PDLC) imprinted with a microlens array (MLA) via solution process to improve the outcoupling efficiency of organic light emitting diodes (OLEDs). The PDLC, well known for its scattering effect, is an excellent technology for improving the outcoupling efficiency of OLEDs. Additionally, we introduce a simple spin-coating process to fabricate PDLC which is adaptable for future solution-processed OLEDs. The MLA-imprinted PDLC applied OLED shows an enhancement factor of 1.22 in outcoupling efficiency which is a 37.5% increase compared to the existing PDLC techniques without changing the electrical properties of the OLED. Through this approach, we can expect the roll-to-roll based extremely flexible OLED, and with further research on pattering PDLC by various templates, higher outcoupling efficiency is achievable through a simple UV irradiation process.
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Affiliation(s)
- Seongmin Lim
- Department of Electronic Engineering, Hanbat National University, Daejeon 34158, Republic of Korea; (S.L.); (H.-S.A.); (E.-J.J.)
| | - Hyeon-Sik Ahn
- Department of Electronic Engineering, Hanbat National University, Daejeon 34158, Republic of Korea; (S.L.); (H.-S.A.); (E.-J.J.)
| | - Eun-Jeong Jang
- Department of Electronic Engineering, Hanbat National University, Daejeon 34158, Republic of Korea; (S.L.); (H.-S.A.); (E.-J.J.)
| | - So-Young Boo
- Department of Creative Convergence Engineering, Hanbat National University, Daejeon 34158, Republic of Korea; (S.-Y.B.); (J.-H.L.)
| | - Akpeko Gasonoo
- Department of Chemistry, University of Calgary, Calgary, AB T2N 1N4, Canada;
| | - Jin-Seog Gwag
- Department of Physics, Yeungnam University, Gyeongsan 38541, Republic of Korea;
| | - Jae-Hyun Lee
- Department of Creative Convergence Engineering, Hanbat National University, Daejeon 34158, Republic of Korea; (S.-Y.B.); (J.-H.L.)
| | - Yoonseuk Choi
- Department of Electronic Engineering, Hanbat National University, Daejeon 34158, Republic of Korea; (S.L.); (H.-S.A.); (E.-J.J.)
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Lee YS, Yoon JH, Raji A, Baek SY, Choi Y, Lee J, Gasonoo A, Lee JH. Optical and Electrical Characterization of Visible Parylene Films. MATERIALS (BASEL, SWITZERLAND) 2022; 15:6717. [PMID: 36234056 PMCID: PMC9572187 DOI: 10.3390/ma15196717] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/01/2022] [Revised: 09/12/2022] [Accepted: 09/23/2022] [Indexed: 06/16/2023]
Abstract
Poly-dichloro-para-xylylene (parylene-C) film is formed through a chemical vapor deposition process, where monomeric gases are polymerized on the target surface at room temperature and are used as transparent insulating coating films. The thin parylene-C films exhibit uniform conformal layers even when deposited on substrates or surfaces with fine cracks, structures, and bumps. However, the film is highly transparent in the visible range (transmittance > 90%); thus, it is difficult to visually identify, inspect the coating process and check for any defects when used as an insulation film. Some reports have demonstrated the deposition of visible (hazy) parylene films through the control of the vaporization or pyrolysis of the parylene-C powder and sublimed dimers, respectively. Even though these films have been applied as device substrates and light extraction layers in organic light-emitting diodes (OLEDs), their optical and electrical characteristics have not been extensively explored, especially for their applications as insulation coatings. In this study, the characteristics of visible parylene films produced by tuning the ratio of dimer to monomer gases via the adjustments of the pyrolysis temperature are analyzed with electrical and optical methods. Parylene-C films deposited within the pyrolysis temperature of 400−700 °C exhibited a haze range of 10−90%. A relative reflectance of 18.8% at 550 nm of the visible light region was achieved in the visible parylene film deposited with a pyrolysis temperature of 400 °C. Resistivity in the order of 1010 Ω cm was achieved for the visible parylene films measured with the transmission line measurement (TLM) method. The films can be applied in advanced insulation coatings for various optical systems and electronic devices.
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Affiliation(s)
- Ye-Seul Lee
- Department of Creative Convergence Engineering, Hanbat National University, 125 Dongseo-daero, Daejeon 34158, Korea
| | - Ji-Hyeon Yoon
- Department of Creative Convergence Engineering, Hanbat National University, 125 Dongseo-daero, Daejeon 34158, Korea
| | - Akeem Raji
- Department of Creative Convergence Engineering, Hanbat National University, 125 Dongseo-daero, Daejeon 34158, Korea
| | - Seung-Yo Baek
- Department of Creative Convergence Engineering, Hanbat National University, 125 Dongseo-daero, Daejeon 34158, Korea
| | - Yoonseuk Choi
- Department of Electronic Engineering, Hanbat National University, 125 Dongseo-daero, Daejeon 34158, Korea
| | - Jonghee Lee
- Department of Creative Convergence Engineering, Hanbat National University, 125 Dongseo-daero, Daejeon 34158, Korea
| | - Akpeko Gasonoo
- Research Institute of Printed Electronics & 3D Printing, Hanbat National University, 125 Dongseo-daero, Daejeon 34158, Korea
| | - Jae-Hyun Lee
- Department of Creative Convergence Engineering, Hanbat National University, 125 Dongseo-daero, Daejeon 34158, Korea
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Kovačič M, Samigullina D, Bouchard F, Krč J, Lipovšek B, Soldera M, Lasagni AF, Reineke S, Topič M. Analysis and optimization of light outcoupling in OLEDs with external hierarchical textures. OPTICS EXPRESS 2021; 29:23701-23716. [PMID: 34614630 DOI: 10.1364/oe.428021] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/16/2021] [Accepted: 06/10/2021] [Indexed: 06/13/2023]
Abstract
Hierarchical textures (combining 2D periodic large and small micro textures) as an external outcoupling solution for OLEDs have been researched, both experimentally and by optical simulations. For the case of a red bottom emitting OLED, different hierarchical textures were fabricated using laser-based methods and a replication step and applied to the OLED substrate, resulting in an increased light outcoupling. Laboratory-size OLED devices with applied textured foils show a smaller increase in efficiency compared to the final large area devices. The results show that the full exploitation of textured foils in laboratory-size samples is mainly limited by the lateral size of the thin film stack area and by limited light collection area of the measuring equipment. Modeling and simulations are used to further evaluate the full prospective of hierarchical textures in large area OLED devices. Optimization of hierarchical textures is done by simultaneously changing the aspect ratios of the small and large textures and a potential of 57% improvement in EQE compared to devices without applied textures is predicted by simulations. Optimized hierarchical textures show similar outcoupling efficiencies compared to optimized single textures, while on the other hand hierarchical textures require less pronounced features, lower aspect ratios, compared to single textures to achieve the same efficiencies. Hierarchical textures also help in eliminating flat parts that limit outcoupling efficiency. Finally, the limiting factors that prevent higher outcoupling are addressed. We show that the dominant factor is non-ideal reflection from the organic thin film stack due to parasitic absorption. In addition, possible ways to further increase the outcoupling from a thick substrate are indicated.
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