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Organic Photovoltaics with Non-Stoichiometric InZnSnO Thin Film Cathodes
Lee, Hye Ji,Noviyana, Imas,Koo, Chang Young,Lee, Jung-A,Kim, Jeong-Joo,Lestari, Annisa Dwi,Jeong, Youngjun,Lee, Youngu,Lee, Hee Young American Scientific Publishers 2017 Journal of Nanoscience and Nanotechnology Vol.17 No.7
<P>Non-stoichiometric indium zinc tin oxide (IZTO) thin films were deposited onto glass substrates at 400 degrees C by DC magnetron sputtering using non-stoichiometric (In0.5Zn0.25-xSn0.25+xO1.5 and In0.4Zn0.3-xSn0.3+xO1.5, where x = +/- 0.05) IZTO ceramic targets. After deposition, all of the films were given annealing treatment at 450 degrees C in argon. The crystallization behavior was examined by X-ray diffraction, while the optical properties were measured by ultraviolet-visible spectroscopy, in which the average transmittance values higher than 80% were observed from all films. The minimum resistivity of approximately 6.3x10(-4) Omega center dot cm was observed from the Sn-rich In0.5Zn0.2Sn0.3O1.5 film. The resistivity values of Sn-rich IZTO thin films were a little smaller than those of Zn-rich IZTO films. An OPV cell with the so-called inverted structure was fabricated using various IZTO films deposited under optimized conditions as the cathode electrode. It was found that the solar cell efficiency could reach up to 7.9% which is the same with the OPV cell with conventional ITO film.</P>
Lee, Donghwa,Lee, Hyungjin,Ahn, Yumi,Jeong, Youngjun,Lee, Dae-Young,Lee, Youngu RSC Pub 2013 Nanoscale Vol.5 No.17
<P>A new AgNW-graphene hybrid transparent conducting electrode (TCE) was prepared by dry-transferring a chemical vapor deposition (CVD)-grown monolayer graphene onto a pristine AgNW TCE. The AgNW-graphene hybrid TCE exhibited excellent optical and electrical properties as well as mechanical flexibility. The AgNW-graphene hybrid TCE showed highly enhanced thermal oxidation and chemical stabilities because of the superior gas-barrier property of the graphene protection layer. Furthermore, the organic solar cells with the AgNW-graphene hybrid TCE showed excellent photovoltaic performance as well as superior long-term stability under ambient conditions.</P>
Lee, Hyungjin,Lee, Donghwa,Ahn, Yumi,Lee, Eun-Woo,Park, Lee Soon,Lee, Youngu RSC Pub 2014 Nanoscale Vol.6 No.15
<P>Highly flexible and efficient silver nanowire-based organic light-emitting diodes (OLEDs) have been successfully fabricated by employing a n-type hole injection layer (HIL). The silver nanowire-based OLEDs without light outcoupling structures exhibited excellent device characteristics such as extremely low turn-on voltage (3.6 V) and high current and power efficiencies (44.5 cd A(-1) and 35.8 lm W(-1)). In addition, flexible OLEDs with the silver nanowire transparent conducting electrode (TCE) and n-type HIL fabricated on plastic substrates showed remarkable mechanical flexibility as well as device performance.</P>
Lee, Donghwa,Lee, Hyungjin,Ahn, Yumi,Lee, Youngu Elsevier 2015 Carbon Vol.81 No.-
<P><B>Abstract</B></P> <P>A sandwich-structured graphene/AgNW/graphene transparent conductive film (TCF) was prepared by embedding silver nanowires (AgNW) network with chemical vapor deposition (CVD)-grown graphene layers. The graphene/AgNW/graphene TCF exhibited excellent optical and electrical properties (88.6% at 550nm and 19.9±1.2Ω/sq), which outperformed commercial indium tin oxide (ITO) film. Moreover, the graphene/AgNW/graphene TCF fabricated on a plastic substrate showed superior mechanical flexibility. In addition to the state of art performance, the reliability and long-term stability of the graphene/AgNW/graphene TCF were greatly enhanced because of the superior gas-barrier property of the graphene as the encapsulation layer. We anticipate that the sandwich-structured graphene/AgNW/graphene TCF can be a promising material to play a great role in realization of emerging optoelectronic devices such as OLEDs, LCDs, TSPs, and OSCs.</P>
1D/2A Terpolymers for High-Efficiency and Long-lived Polymer Solar Cells
Youngu Lee(이윤구) 한국고분자학회 2021 한국고분자학회 학술대회 연구논문 초록집 Vol.46 No.2
Terpolymers consisting of three different monomers in the polymer backbone have emerged as promising p-type polymers for polymer solar cells (PSCs). The incorporation of a third monomer into a donor-acceptor (D-A) copolymer backbone can create numerous combinations that may have a synergetic effect on physicochemical properties such as light harvesting ability, miscibility, charge carrier mobility, energy levels and crystallinity. Moreover, the random arrangement of terpolymer can reduce the degree of regularity in the polymer backbone, thereby enabling high solubility in non-halogenated solvents. However, despite the various merits, terpolymer-based PSCs processed with non-halogenated solvents still have shown poor photovoltaic performance and long-term stability. In this talk, I will present the synthesis and characterization of novel 1D/2A terpolymers composed of one donor and two acceptors for high-efficiency and long-lived PSCs processed with non-halogenated solvents.
Lee, Donghwa,Kim, Jongyoun,Kim, Honggi,Heo, Hyojung,Park, Kyutae,Lee, Youngu The Royal Society of Chemistry 2018 Nanoscale Vol.10 No.39
<P>An ultra-sensitive and transparent piezoresistive pressure sensor based on a sea-urchin shaped metal nanoparticle (SSNP)-polyurethane (PU) composite with microdome arrays is successfully fabricated for the first time. The piezoresistive pressure sensor with microdome arrays was prepared using a nanoimprinting process based on an intermediate polymer substrate (IPS) replica mold. It showed a superior sensitivity (71.37 kPa<SUP>−1</SUP>) and a high optical transmittance (77.7% at 550 nm) due to the effective quantum tunneling effect even at small concentrations of conductive SSNP filler (6 mg mL<SUP>−1</SUP>). The high-performance characteristics of the piezoresistive pressure sensor are attributed to the geometric effects of the microdome structure, especially the stress concentration at small contact spots and the deformation of the contact area. The piezoresistive pressure sensor with microdome arrays also exhibited a fast response/relaxation time (30 ms), ultra-low pressure detection (4 Pa), and excellent long-term stability under harsh conditions. In addition, the effectiveness of the piezoresistive pressure sensors in various sensing applications including sensing mapping, human arterial pulse monitoring, and the detection of muscle movement is also successfully demonstrated. It is anticipated that this novel transparent pressure sensor based on a SSNP-PU composite with microdome arrays will be a key component in the development of integrated transparent sensing applications.</P>
Highly Conductive and Flexible Silver Nanowire-Based Microelectrodes on Biocompatible Hydrogel
Ahn, Yumi,Lee, Hyungjin,Lee, Donghwa,Lee, Youngu American Chemical Society 2014 ACS APPLIED MATERIALS & INTERFACES Vol.6 No.21
<P>We successfully fabricated silver nanowire (AgNW)-based microelectrodes on various substrates such as a glass and polydimethylsiloxane by using a photolithographic process for the first time. The AgNW-based microelectrodes exhibited excellent electrical conductivity and mechanical flexibility. We also demonstrated the direct transfer process of AgNW-based microelectrodes from a glass to a biocompatible polyacrylamide-based hydrogel. The AgNW-based microelectrodes on the biocompatible hydrogel showed excellent electrical performance. Furthermore, they showed great mechanical flexibility as well as superior stability under wet conditions. We anticipate that the AgNW-based microelectrodes on biocompatible hydrogel substrates can be a promising platform for realization of practical bioelectronics devices.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2014/aamick.2014.6.issue-21/am504462f/production/images/medium/am-2014-04462f_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am504462f'>ACS Electronic Supporting Info</A></P>