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Kim, Jeonghun,Koh, Jong Kwan,Kim, Byeonggwan,Ahn, Sung Hoon,Ahn, Hyungju,Ryu, Du Yeol,Kim, Jong Hak,Kim, Eunkyoung WILEY‐VCH Verlag 2011 Advanced Functional Materials Vol.21 No.24
<P>An iodine‐free solid‐state dye‐sensitized solar cell (ssDSSC) with 6.8% efficiency can be fabricated using conductive polymers and organized mesoporous TiO<SUB>2</SUB>. On page 4633, Eunkyoung Kim, Jong Hak Kim, and co‐workers show the effects of polymer conductivity and transmittance of the interfacial TiO<SUB>2</SUB> layer on energy conversion efficiency. This method can be used for the fabrication of various photovoltaic cells. </P>
Electronic structure of detwinned BaFe2As2from photoemission and first principles
Kim, Yeongkwan,Oh, Hyungju,Kim, Chul,Song, Dongjoon,Jung, Wonsig,Kim, Beomyoung,Choi, Hyoung Joon,Kim, Changyoung,Lee, Bumsung,Khim, Seunghyun,Kim, Hyungjoon,Kim, Keehoon,Hong, Jongbeom,Kwon, Yongseun American Physical Society 2011 Physical review. B, Condensed matter and materials Vol.83 No.6
Unusual Li-ion storage through anionic redox processes of bacteria-driven tellurium nanorods
Kim, Min Gyu,Kim, Dong-Hun,Kim, Taeyang,Park, Sunhwa,Kwon, Gukyoung,Kim, Mi Sug,Shin, Tae Joo,Ahn, Hyungju,Hur, Hor-Gil The Royal Society of Chemistry 2015 Journal of Materials Chemistry A Vol.3 No.33
<▼1><P>Li-ion storage through an anionic redox process of biogenic tellurium nanorods to provide biogeochemistry with new insight into energy science.</P></▼1><▼2><P>The bacterial respiration process enables the facile and morphologically-selective preparation of nanomaterials, along with the removal of environmentally toxic elements. Bacteria-driven metallic tellurium Te(0) nanorods formed extra- and intracellularly by <I>Shewanella oneidensis</I> MR-1, consisting of a helically-twisted atomic-wire bundle structure, exhibited distinct Li-ion uptake properties after direct or glucose-assisted surface-carbonization of bacterial cells. By synchrotron-based <I>in situ</I> structural characterization during cycling, it was demonstrated that the carbonized polycrystalline Te materials experience phase transition to Li2Te through simple Li-ion diffusion and charge compensation by the anionic redox reaction of metallic Te to polyanionic telluride (Ten<SUP>2−</SUP>). On the other hand, the carbonized amorphous Te materials show simple Li-ion accumulation around Te element with only the anionic redox reaction. The gradual generation of electrostatic interactions between Li<SUP>+</SUP> and Ten<SUP>2−</SUP> ion pairs promotes host lattice stabilization, unlike in other metallic anode systems with volume expansion. We report that the unusual anionic redox chemistry of Te with its structural flexibility drives the reversible Li-ion uptake without any critical structural deterioration, highlighting the potential of tellurium as a new energy conversion and storage material.</P></▼2>
Lee, Wonho,Kim, Jae-Han,Kim, Taesu,Kim, Seonha,Lee, Changyeon,Kim, Jin-Seong,Ahn, Hyungju,Kim, Taek-Soo,Kim, Bumjoon J. The Royal Society of Chemistry 2018 Journal of Materials Chemistry A Vol.6 No.10
<P>In this study, we demonstrate that the introduction of small amounts of phenyl-C71-butyric acid methyl ester (PC71BM) into all-polymer solar cells (all-PSCs) increases the photovoltaic performance without compromising mechanical properties. Ternary blend polymer solar cells (ternary-PSCs) consisting of a polymer donor (PTB7-Th) and an acceptor mixture with different weight ratios of a polymeric acceptor (P(NDI2HD-T2)) and PC71BM demonstrate the effects of PC71BM loading on the power conversion efficiency (PCE) and mechanical properties. A significant enhancement in the PCEs of ternary-PSCs, from 6.32% to 7.33%, is observed when PC71BM is added into the active layer as up to 30 wt% of the acceptor mixture. Importantly, the excellent mechanical properties (<I>i.e.</I>, crack onset strain = 11.6%, toughness = 2237 J m<SUP>−3</SUP>) of the blend films are well preserved at PC71BM loadings at or below 30 wt%. In contrast, both the PCE and the mechanical performance of the ternary-PSCs significantly decrease at higher PC71BM loadings (>50 wt%). Detailed morphological analysis<I>via</I>grazing incidence X-ray scattering measurements reveals that PC71BM molecules are well-dispersed in the amorphous portion of the active layer at PC71BM loadings up to 30 wt%. Therefore, both the mechanical and photovoltaic performances of the ternary-PSCs correlate closely with their morphological behavior, particularly in terms of the mixing behavior of PC71BM with polymers. The well-dispersed PC71BM molecules in the amorphous polymer domains facilitate efficient exciton dissociation, whereas the formation of PC71BM aggregates above a critical concentration causes severe mechanical degradation of the ternary-PSCs due to the presence of weak interfaces between the brittle PC71BM and polymer domains. Therefore, the ternary blends with optimal content of polymer/fullerene acceptors represent important candidates for flexible and wearable solar cells that require both high mechanical and photovoltaic performances.</P>
Small-angle X-ray Scattering Beamline BL4C SAXS at Pohang Light Source II
Kwang-Woo Kim,Jehan Kim,Young Duck Yun,Hyungju Ahn,Byoungseok Min,Na Hyung Kim,Seungyu Rah,Hyo-Yun Kim,Chae-Soon Lee,In Deuk Seo,Woul-Woo Lee,Hyeong Joo Choi,Kyeong Sik Jin 한국구조생물학회 2017 Biodesign Vol.5 No.1
BL4C SAXS at the Pohang Light Source II is a small-angle X-ray scattering beamline based on an in-vacuum undulator insertion device, Si(111) DCM, and toroidal focusing mirror. The beamline normally provides high-flux synchrotron radiation X-ray sources with energies from 10.3 to 20.6 keV and a 100 µm (vertical) × 300 µm (horizontal) full width at half-maximum focal spot. The analysis of the SAXS data would be facilitated by means of useful ancillary equipment. The design of the beamline, the key components, and its role are described.
Kim, Yeongsik,Yong, Daeseong,Lee, Wooseop,Jo, Seongjun,Ahn, Hyungju,Kim, Jaeup U.,Ryu, Du Yeol American Chemical Society 2018 Macromolecules Vol.51 No.21
<P>We present a compelling evidence for thickness dependence on the order-to-disorder transition (ODT) behavior in cylinder- and lamella-forming polystyrene-<I>b</I>-poly(2-vinylpyridine) (PS-<I>b</I>-P2VP) films. Such an asymmetric wetting condition that confines the films with selective interactions of the PS/air and P2VP/substrate interfaces generates a parallel orientation of cylindrical and lamellar microdomains. We evaluated thickness-dependent phase transition as a function of interlattice distance (<I>L</I><SUB>0</SUB>) using <I>ex situ</I> grazing incidence small-angle X-ray scattering (GISAXS) and transmission electron microscopy (TEM). Below an onset thickness (<I>t</I><SUB>0</SUB>) above which the ODT temperatures (<I>T</I><SUB>ODT</SUB>s) of the films are independent of film thickness, the <I>T</I><SUB>ODT</SUB>s of cylinder- and lamella-forming PS-<I>b</I>-P2VP films remarkably increase as the film thickness decreases. Our results confirmed that preferential wetting at the PS/air and P2VP/substrate interfaces in very thin films substantially leads to an ordered state over accessible temperature range up to ∼260 °C. More interestingly, the <I>t</I><SUB>0</SUB> of lamellar morphology (∼22<I>L</I><SUB>0</SUB>) is thicker than that of cylindrical morphology (∼10<I>L</I><SUB>0</SUB>), indicating that the interfacial interactions are more influential to a 1D multilayer structure of lamellar microdomains than a 2D hexagonally packed order of parallel cylinders. Our theoretical calculation utilizing the self-consistent field theory (SCFT) of a discrete bead-spring model with finite-range interactions exhibited the similar thickness dependence of ODTs for cylinder- and lamella-forming PS-<I>b</I>-P2VP films confined in such an asymmetric wetting condition.</P> [FIG OMISSION]</BR>
Kim, Eunhye,Ahn, Hyungju,Park, Sungmin,Lee, Hoyeon,Lee, Moongyu,Lee, Sumi,Kim, Taewoo,Kwak, Eun-Ae,Lee, Jun Han,Lei, Xie,Huh, June,Bang, Joona,Lee, Byeongdu,Ryu, Du Yeol American Chemical Society 2013 ACS NANO Vol.7 No.3
<P>The directed assembly of block copolymer nanostructures with large periods exceeding 100 nm remains challenging because the translational ordering of long-chained block copolymer is hindered by its very low chain mobility. Using a solvent-vapor annealing process with a neutral solvent, which was sequentially combined with a thermal annealing process, we demonstrate the rapid evolution of a perpendicularly oriented lamellar morphology in high molecular weight block copolymer films on neutral substrate. The synergy with the topographically patterned substrate facilitated unidirectionally structural development of ultrahigh molecular weight block copolymer thin filmseven for the structures with a large period of 200 nmleading to perfectly guided, parallel, and highly ordered line-arrays of perpendicularly oriented lamellae in the trenched confinement. This breakthrough strategy, which is applicable to nanolithographic pattern transfer to target substrates, can be a simple and efficient route to satisfy the demand for block copolymer assemblies with larger feature sizes on hundreds of nanometers scale.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2013/ancac3.2013.7.issue-3/nn3051264/production/images/medium/nn-2012-051264_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn3051264'>ACS Electronic Supporting Info</A></P>