Investigation of dry-deposited ion storage layers using various oxide particles to enhance electrochromic performance

Choi, Dahyun,Lee, Minji,Kim, Hyungsub,Chu, Won-shik,Chun, Doo-man,Ahn, Sung-Hoon,Lee, Caroline Sunyong North-Holland 2018 Solar Energy Materials and Solar Cells Vol. No.

<P><B>Abstract</B></P> <P>Various ion storage layers were fabricated on ITO-glass substrates by a dry deposition process to study their effects in electrochromic devices. Dense nickel oxide (NiO) film was formed using micro-sized NiO particles, a porous film was formed using nano-sized NiO particles, and a porous antimony tin oxide (ATO) film was formed using nano-sized ATO particles. Electrochemical analyses revealed that the nano-porous NiO layer had a high charge capacity with a low charge transfer resistance. Moreover, an electrochromic device using a NiO film with nano-sized pores had an optical transmittance difference of 42% and a stable cyclic transmittance for 1h at a wavelength of 630nm. We assessed the effects of the different ion storage layers by evaluating the electrochromic device in terms of the following important properties: 1) high charge capacity, 2) low charge transfer resistance at the interface between film and electrolyte, and 3) high diffusion rate from film to electrolyte. Based on these criteria, we found that the ion storage layer formed with nano-sized NiO particles best satisfied these conditions. Finally, we confirmed that stable and high electrochromic performance can be achieved through improving these properties in ion storage layers.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Ion storage (IS) layer fabricated by dry deposition method using various sized NiO. </LI> <LI> NiO film resulting in nano-sized pores, showed high charge capacity with low transfer resistance. </LI> <LI> Device using Nano NiO film showed a transmittance difference of 42% with stable switching at 630nm. </LI> <LI> Stable and high electrochromic performance can be achieved by adding metal oxide based IS layers. </LI> </UL> </P>

Low-voltage modulated inorganic smart windows using solid polymer electrolyte

Choi, Dahyun,Kim, Hyojun,Lee, Minji,Son, Minhee,Ahn, Sung-hoon,Lee, Caroline Sunyong North-Holland 2019 Solar Energy Materials and Solar Cells Vol. No.

<P><B>Abstract</B></P> <P>We have developed a low-voltage modulated inorganic electrochromic device using a solid polymer electrolyte (SPE). UV-cured electrolytes with various ferrocene (Fc) concentrations of 0, 0.05, and 0.1 M were developed. The electrochromic evaluation of the device using an Fc concentration of 0.1 M indicated high transmittance changes of >60% under a low potential change of 2.5 V due to the Fc in the electrolyte assisting with ion transfer to thin films, resulting in the lowest resistance within the device. Moreover, this electrochromic device, with an excellent self-bleaching effect, showed improved transmittance by 37% for 2000 s.</P> <P>We have fabricated a large smart window with a size of 20 × 20 cm<SUP>2</SUP> using the optimized conditions, with stable cyclic transmittance change up to 100 cycles upon a potential change of 2.5 V. Therefore, an electrochromic device with high transmittance difference and stable switching performance was successfully demonstrated using 0.1 M Fc-based SPE.</P> <P><B>Highlights</B></P> <P> <UL> <LI> WO<SUB>3</SUB> electrochromic and ATO ion storage layers were deposited on the FTO-glass using a kinetically sprayed process. </LI> <LI> The electrochromic device with Ferrocene shows low resistance, resulting in a transmittance change of >60% upon low voltage. </LI> <LI> The ECD with 0.1 M Fc showed the highest self-bleaching effect for cyclic transmittance without additional external voltage. </LI> <LI> We have proven that a large-area smart window was fabricated and operated under the low voltage change of 2.5 V. </LI> </UL> </P>

Application of the Taguchi Method to Optimize Graphene Coatings on Copper Nanoparticles Formed Using a Solid Carbon Source

Choi, Dahyun,Pyo, Youngjun,Jung, Seung-Boo,Kim, Yongil,Yoon, Eric H.,Lee, Caroline Sunyong JAPAN INSTITUTE OF METALS 2016 MATERIALS TRANSACTIONS Vol.57 No.7

<P>Graphene has attracted much recent interest as an electronic material due to its large electron mobility. Large-area graphene has been synthesized using chemical vapor deposition (CVD). however, it is difficult to apply this process to grow graphene on nanoparticles (NPs) because of their small radius of curvature, which results in a large defect density. In this work, we used the Taguchi method to optimize the deposition of graphene on nanoparticles. We used polyvinylpyrrolidone (PVP) to coat copper NPs via CVD and optimized the process conditions using a minimal number of experiments. The PVP served as the solid carbon source, forming graphene when heated to 875 degrees C. To improve the quality of the graph one coatings on the Cu NPs, the following process parameters wore Ng-tried: gas conditions (ratio of Ar to H-2), process time and temperature, the amount of PVP solution, and the molecular weight of PVP. We identified optimal process conditions using only eight experiments. Raman spectroscopy was used to analyze the quality of the graphene coatings by comparing two-dimensional (20) spectra and I-D/I-G ratios of the different coatings. A decrease in I-D/I-G, in combination with sharper Raman bands, is indicative of the thickness and crystal quality of the graphene layer. The quality of the graphene layer was also evaluated using transmission electron microscopy (TEM) and scanning electron microscopy (SUM). The optimal conditions for the formation of graphene-coated Cu NPs were: a temperature of 875 degrees C, a deposition time of 2 minutes, an Ar-to-H-2 ratio of 1:1, PVP with a molecular weight of M-w = 3,500 (K-12) during the polyol process, and a 50-wt.% PVP solution with M-W = 45,000 (K-30). Using the Taguchi method, we identified trends relating defect density versus process conditions and successfully obtained a graphene coating with a minimal defect density.</P>

Fabrication of transparent conductive tri-composite film for electrochromic application

Choi, Dahyun,Lee, Minji,Kim, Hyungsub,Chu, Won-shik,Chun, Doo-man,Ahn, Sung-Hoon,Lee, Caroline Sunyong Elsevier 2017 APPLIED SURFACE SCIENCE - Vol.425 No.-

<P><B>Abstract</B></P> <P>A transparent conductive electrode (TCE) based on poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) was developed using a dry deposition method for application as an electrochromic (EC) device. To improve its electrical conductivity and stable EC performance, AgNW and TiO<SUB>2</SUB> nanoparticles were included in the TCE film. The resulting TiO<SUB>2</SUB>/AgNW/PEDOT:PSS hybrid film showed electrical sheet resistivity of 23Ω/sq., similar to that of a commercial TCE film. When +2.0V was applied to the hybrid film, the response current was stable, maintaining a value of 2.0mA. We found that the hybrid film could be used as an EC device, without using commercial TCE film. Antimony-doped tin oxide on indium-doped tin oxide-glass as an ion-storage layer was combined with the hybrid film, with 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-TFSI) injected into the EC device as an ionic liquid electrolyte. The optical transmittance difference between the colored and bleached states was 23% at 630nm; under applied voltages of −2.0V and +2.0V, the coloration efficiency was 127.83cm<SUP>2</SUP>/C. Moreover, cyclic transmittance with switching voltage for 3h showed stable optical transmittance of 31% at 630nm. Cyclic voltammetry measurements indicated stable behavior over 50 cycles. Thus, the proposed TCE configuration (TiO<SUB>2</SUB>/AgNW/PEDOT:PSS) shows great potential as a substitute for commercial TCEs, the cost of which depends on the availability of rare-earth materials.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Tri-composite film composed of TiO<SUB>2</SUB>/AgNW/PEDOT:PSS for transparent conductive electrode (TCE),was developed to be used for electrochromic device. </LI> <LI> This Tri-composite film showed low electrical sheet resistivity, comparable to that of TCE and maintained stable response current with voltage application of +2.0V. </LI> <LI> This electrochromic device using ITO-free TCE, showed coloration efficiency of 127.83cm<SUP>2</SUP>/C. </LI> <LI> Dry deposited TiO2 film shows nanoporous <I>p</I>-<I>n</I> heterostructure to improve electrochemical performance of the device. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

One Million Cycle Durability Test of Electrochromic Devices Using Charge Balance Control

In-Gyu Choi,Dahyun Choi,Jang-Yeob Lee,Minji Lee,Sung-Ik Park,Doo-Man Chun,Caroline Sunyong Lee,Won-Shik Chu 한국정밀공학회 2020 International Journal of Precision Engineering and Vol.7 No.1

We fabricated 10 mm × 10 mm WO3 electrochromic devices (ECDs) using a nanoparticle deposition system (NPDS), which is a coating method that uses kinetic spray. NPDS has the advantage of mass production due to its relatively low pressure and low temperature working conditions but can result in porous surfaces, which has a negative effect on device durability. We developed an optical transmittance measurement and voltage control system that allows dynamic control. Transmittance was measured by Optical Power Meter, 2936-R Newport, while voltage was dynamically applied by NI9477, National Instrument. Current was measured by high resolution current, National Instrument. This system enables ECDs to be feedback controlled depending on the measured electronic properties. We then characterized the WO3 ECDs, focusing on the relationship between transmittance and current under well-known static operating conditions. Finally, we proposed a new algorithm to extend durability performance by adopting charge balance control and conducted an accelerated life test over 1,000,000 cycles. According to our results, the optical performance was maintained until the test ended, and there was a 45.4% difference in the maximum and minimum transmittance of the sample after the accelerated life test. Therefore, the charge balance control enhanced the lifetime of the ECDs by avoiding negative charge accumulation, verifying that the durability of ECDs could be enhanced by adopting dynamic control.

Higher food literacy scores are associated with healthier diet quality in children and adolescents: the development and validation of a two-dimensional food literacy measurement tool for children and adolescents

Dahyun Park,Mi-Kyung Choi,Yoo Kyoung Park,Clara Yongjoo Park,Min-Jeong Shin 한국영양학회 2022 Nutrition Research and Practice Vol.16 No.2

BACKGROUND/OBJECTIVES: Most child and adolescent food literacy measurement tools focus on nutrition and food safety. However, the importance of aspects related to the food system such as food distribution and food waste and their effects on environmental sustainability is growing. We therefore developed and validated a two-dimensional tool for children (8–12 years old) and adolescents (13–18 years old) that can comprehensively measure food literacy. The association of food literacy with diet quality and self-reported health was assessed. SUBJECTS/METHODS: First, we developed a food literacy conceptual framework that contains food system and literacy dimensions through a literature review, focus group interviews, and expert review. After a face validity study, we conducted the main survey (n = 200) to validate the questionnaire. Construct validity and reliability were assessed using exploratory factor analysis (EFA), confirmatory factor analysis (CFA), and Cronbach"s alpha. RESULTS: As a result of the Delphi study, content validity was confirmed for the remaining 30 items after two items were excluded (content validity ratio = 0.86). Eleven items were excluded from the EFA results, while the CFA results indicated appropriate fit indices for the proposed model (comparative fit index = 0.904, root mean square error of approximation = 0.068). The final food literacy questionnaire consisted of 19 questions and comprised 5 factors: production, distribution, selection, preparation and cooking, and intake. Food literacy was positively associated with diet quality, as assessed by the Nutrition Quotient score, in both children and adolescents and with self-reported health in adolescents. CONCLUSIONS: Based on this integrated conceptual framework, a two-dimensional 19-item food literacy measurement tool was developed and verified for practical use to improve the diet quality and food-related environmental sustainability awareness of children and adolescents.

Association Between Serum Triglycerides and Cerebral Amyloidosis in Cognitively Normal Elderly

Choi, Hyo Jung,Byun, Min Soo,Yi, Dahyun,Choe, Young Min,Sohn, Bo Kyung,Baek, Hye Won,Lee, Jun Ho,Kim, Hyun Jung,Han, Ji Young,Yoon, Eun Jin,Kim, Yu Kyeong,Woo, Jong Inn,Lee, Dong Young Elsevier 2016 The American journal of geriatric psychiatry Vol.24 No.8

Single-cell capacitance analysis of NIH/3T3 cells using an impedance biosensor

Kang Dahyun,Kim Yeeun,Lee Gayoung,Choi Jisoo,Yang Jeongmok,Jang Moongyu 한국물리학회 2023 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.83 No.11

Biosensors have emerged as promising tools for the analysis of single-cell growth. This study focuses on the fabrication of an impedance biosensor to monitor the growth of NIH/3T3 cells by measuring changes in their capacitance over time. The results showed an increase in capacitance corresponding to the growth of the cells. However, it was observed that the capacitance behaved diferently in the early (0–2.33 h) and late (2.33–48 h) stages of cell growth. In the early stage, the cells in the medium were still in a sinking state, whereas in the late stage, most of the cells were in contact with the sensor surface, undergoing growth and division. As a result, the late-stage capacitance was higher than the early stage capacitance. The average capacitance values of a single cell were recorded at diferent frequencies and showed the same phenomenon at all frequencies.

탄소 나노 튜브를 활용한 고정밀도 및 전기전도성의 복합재 3D 프린팅

임다현(Dahyun Daniel Lim),이재민(Jaemin Lee),최원준(Wonjoon Choi) 대한기계학회 2020 대한기계학회 춘추학술대회 Vol.2020 No.12

연속 회분식 반응조 운전(SBR)에서 아세트아미노펜(Acetaminophen)이 미치는 영향

이다현(Dahyun Lee),최정동(Jeongdong Choi) 대한환경공학회 2022 대한환경공학회 학술발표논문집 Vol.2022 No.11