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RISS 인기검색어
- 검색키워드
- 저자 : Bonkee Kim (검색결과 4 건)
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Kim, Jigeon,Koo, Bonkee,Kim, Wook Hyun,Choi, Jongmin,Choi, Changsoon,Lim, Sung Jun,Lee, Jong-Soo,Kim, Dae-Hwan,Ko, Min Jae,Kim, Younghoon Elsevier 2019 Nano energy Vol.66 No.-
<P><B>Abstract</B></P> <P>Fully inorganic CsPbI<SUB>3</SUB> perovskite quantum dots (CsPbI<SUB>3</SUB>-PQDs) are known as the best-performing photovoltaic absorber in colloidal quantum dot solar cells. This is achieved by improving the cubic-phase-stabilization and electronic-coupling in CsPbI<SUB>3</SUB>-PQD solids. In conventional approaches, the hydrolysis of methyl acetate (MeOAc) resulting in acetic acid and methanol as intermediate substances plays a key role in replacing long-chain hydrocarbons with short-chain ligands, which improves charge transport in the CsPbI<SUB>3</SUB>-PQD solids. However, CsPbI<SUB>3</SUB>-PQDs suffer from lattice distortion and instability under acidic conditions including protons and polar media, leading to CsPbI<SUB>3</SUB>-PQD fusion and poor photovoltaic performance. Herein, we report that electronic coupling and photovoltaic performance of CsPbI<SUB>3</SUB>-PQD solids are improved by efficient removal of long-chain oleate ligands using a solution of sodium acetate (NaOAc) in MeOAc, which results in the direct generation of OAc ions without forming protons and methanol. NaOAc-based ligand exchange of CsPbI<SUB>3</SUB>-PQDs enables preservation of their nanocrystal size without fusion and minimization of surface trap states originating from metal hydroxide formation on their surfaces. Consequently, the best solar cell comprising NaOAc-treated CsPbI<SUB>3</SUB>-PQDs shows an improved device performance with a power conversion efficiency (<I>PCE</I>) of 13.3%, as compared with a lead nitrate-treated control device (12.4% <I>PCE</I>).</P> <P><B>Highlights</B></P> <P> <UL> <LI> NaOAc directly generates short-chain OAc ions to exchange the oleate ligands of CsPbI<SUB>3</SUB>-PQDs. </LI> <LI> Our strategy enables minimizing the formation of protons and methanol during the ligand exchange. </LI> <LI> NaOAc-based ligand exchange enables preserving nanocrystal size and minimizing surface traps. </LI> <LI> Resultant CsPbI<SUB>3</SUB>-PQD solids show enhanced electronic coupling with improved charge transport. </LI> <LI> NaOAc-treated CsPbI<SUB>3</SUB>-PQD solar cells show improved photovoltaic performance up to 13.33% PCE. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>We demonstrate that sodium acetate (NaOAc) directly generates short-chain OAc ions to exchange the long-chain oleate ligands of CsPbI<SUB>3</SUB> perovskite quantum dots (CsPbI<SUB>3</SUB>-PQDs). NaOAc-based ligand exchange enables preservation of CsPbI<SUB>3</SUB>-PQD size, minimization of surface trap states, and enhancement of electronic coupling in the resultant CsPbI<SUB>3</SUB>-PQD solids. Consequently, NaOAc-treated CsPbI<SUB>3</SUB>-PQD solar cells show improved device performance with 12.4% power conversion efficiency.</P> <P>[DISPLAY OMISSION]</P>
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Transparent 3 nm-thick MoS<sub>2</sub> counter electrodes for bifacial dye-sensitized solar cells
Jeong, Taehee,Ham, So-Yeon,Koo, Bonkee,Lee, Phillip,Min, Yo-Sep,Kim, Jae-Yup,Ko, Min Jae Elsevier 2019 Journal of industrial and engineering chemistry Vol.80 No.-
<P><B>Abstract</B></P> <P>Molybdenum disulfide (MoS<SUB>2</SUB>) counter electrode (CE) is considered one of the most viable alternatives to Pt CE in dye-sensitized solar cells (DSSCs) owing to its abundance, low cost, and superior electrocatalytic activity. However, mostly, MoS<SUB>2</SUB> CEs for DSSCs are prepared by conventional chemical reactions and annealing at a high temperature. By these conventional processes, deposition of sufficiently thin and transparent MoS<SUB>2</SUB> layers is challenging; therefore, bifacial DSSCs employing transparent MoS<SUB>2</SUB> CEs have not been studied. Here, we report transparent few-nanometer-thick MoS<SUB>2</SUB> CEs prepared by atomic layer deposition at a relatively low temperature (98°C) for bifacial DSSC applications. MoS<SUB>2</SUB> nanofilms with precisely controlled thicknesses of 3–16nm are conformally coated on transparent conducting oxide glass substrates. With increase in the MoS<SUB>2</SUB> nanofilm thickness, the MoS<SUB>2</SUB> CE electrocatalytic activity for the iodide/triiodide redox couple enhances, but its transparency decreases. Notably, the application of a thinner MoS<SUB>2</SUB> nanofilm in a bifacial DSSC leads to lower conversion efficiency under front-illumination, but higher conversion efficiency under back-illumination. In particular, only the 3nm-thick MoS<SUB>2</SUB> nanofilm shows reasonable photovoltaic performances under both front- and back-illumination conditions.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
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Baek, Hyunhee,Lee, Chanwoo,Park, Jeongju,Kim, Younghoon,Koo, Bonkee,Shin, Hyunjung,Wang, Dayang,Cho, Jinhan The Royal Society of Chemistry 2012 Journal of materials chemistry Vol.22 No.11
<P>Electrochemical properties of enzymes are of fundamental and practical importance in bio-electrochemical applications. These redox properties, which can cause the reversible changes in the current according to their redox reactions in solution, often depend on the chemical activity of transition metal ions as cofactors within the active sites of enzymes. Here, we demonstrate that the reversible resistance changes in enzyme-based multilayer films can be caused by the externally applied voltage as a result of charge trap/release of haem Fe<SUP>III</SUP>/Fe<SUP>II</SUP> redox couples in dry form. It is also demonstrated that the electrically bistable switching properties of redox enzymes can be applied to nonvolatile memory devices requiring low power consumption. For this study, cationic poly(allylamine hydrochloride) (PAH) was alternately layer-by-layer assembled with anionic catalase enzyme onto Pt-coated substrates until the desired number of layers was deposited. A top electrode was deposited onto (PAH/catalase)<SUB><I>n</I></SUB> multilayer films to complete device fabrication. When an external bias was applied to the devices, a switching phenomenon depending on the voltage polarity (<I>i.e.</I>, bipolar switching) was observed at low operating voltages (RESET at 1.8 V and SET voltage at −1.5 V), fast switching speed at the nanosecond level, and an ON/OFF current ratio of ∼10<SUP>2</SUP>. In the case of inserting insulating layers of about 2 nm thickness between adjacent catalase (CAT) layers, these devices exhibited the higher memory performance (ON/OFF current ratio of ∼10<SUP>6</SUP>) and the lower power consumption than those of (PAH/CAT)<SUB>15</SUB> multilayer devices.</P> <P>Graphic Abstract</P><P>We demonstrate that the redox enzymes can be used as electrically active materials for nonvolatile memory devices and that, furthermore their switching behavior originates from redox sites within enzymes. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c2jm16231h'> </P>
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