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Kim, Sun Hong,Seo, Hyunseon,Kang, Jiheong,Hong, Jaeyoung,Seong, Duhwan,Kim, Han-Jin,Kim, Jaemin,Mun, Jaewan,Youn, Inchan,Kim, Jinseok,Kim, Yu-Chan,Seok, Hyun-Kwang,Lee, Changhee,Tok, Jeffrey B.-H.,Bao American Chemical Society 2019 ACS NANO Vol.13 No.6
<P>Both self-healable conductors and stretchable conductors have been previously reported. However, it is still difficult to simultaneously achieve high stretchability, high conductivity, and self-healability. Here, we observed an intriguing phenomenon, termed ?electrical self-boosting?, which enables reconstructing of electrically percolative pathways in an ultrastretchable and self-healable nanocomposite conductor (over 1700% strain). The autonomously reconstructed percolative pathways were directly verified by using microcomputed tomography and <I>in situ</I> scanning electron microscopy. The encapsulated nanocomposite conductor shows exceptional conductivity (average value: 2578 S cm<SUP>?1</SUP>; highest value: 3086 S cm<SUP>?1</SUP>) at 3500% tensile strain by virtue of efficient strain energy dissipation of the self-healing polymer and self-alignment and rearrangement of silver flakes surrounded by spontaneously formed silver nanoparticles and their self-assembly in the strained self-healing polymer matrix. In addition, the conductor maintains high conductivity and stretchability even after recovered from a complete cut. Besides, a design of double-layered conductor enabled by the self-bonding assembly allowed a conducting interface to be located on the neutral mechanical plane, showing extremely durable operations in a cyclic stretching test. Finally, we successfully demonstrated that electromyogram signals can be monitored by our self-healable interconnects. Such information was transmitted to a prosthetic robot to control various hand motions for robust interactive human-robot interfaces.</P> [FIG OMISSION]</BR>
Kim, Jun Young,Cho, Eunae,Kim, Jaehoon,Shin, Hyeonwoo,Roh, Jeongkyun,Thambidurai, Mariyappan,Kang, Chan-Mo,Song, Hyung-Jun,Kim, SeongMin,Kim, Hyeok,Lee, Changhee Optical Society of America 2015 Optics express Vol.23 No.19
<P>We demonstrate that nanocrystalline Al-doped zinc oxide (n-AZO) thin film used as an electron-extraction layer can significantly enhance the performance of inverted polymer solar cells based on the bulk heterojunction of poly[[9-(1-octylnonyl)-9H-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5-thiophenediyl] (PCDTBT) and [6,6]-phenyl C<sub>71</sub>-butyric acid methyl ester (PC<sub>70</sub>BM). A synergistic study with both simulation and experiment on n-AZO was carried out to offer a rational guidance for the efficiency improvement. As a result, An n-AZO film with an average grain size of 13 to 22 nm was prepared by a sol-gel spin-coating method, and a minimum resistivity of 2.1 ?? 10<sup>-3</sup> 곽·cm was obtained for an Al-doping concentration of 5.83 at.%. When an n-AZO film with a 5.83 at.% Al concentration was inserted between the ITO electrode and the active layer (PCDTBT:PC<sub>70</sub>BM), the power conversion efficiency increased from 3.7 to 5.6%.</P>
Kim, Jung Yong,Noh, Seunguk,Nam, Young Min,Kim, Jun Young,Roh, Jeongkyun,Park, Myeongjin,Amsden, Jason J.,Yoon, Do Y.,Lee, Changhee,Jo, Won Ho American Chemical Society 2011 ACS APPLIED MATERIALS & INTERFACES Vol.3 No.11
<P>The effect of a nanoscale boron subphthalocyanine chloride (SubPc) interfacial layer on the performance of inverted polymer solar cells based on poly (3-hexyl thiophene) (P3HT) and [6,6]-phenyl-C<SUB>71</SUB>-butyric acid methyl ester (PC<SUB>71</SUB>BM) was studied. When a 1 nm SubPc layer was introduced between the active layer (P3HT:PC<SUB>71</SUB>BM) and MoO<SUB><I>x</I></SUB> in the device with ITO/ZnO/P3HT:PC<SUB>71</SUB>BM/SubPc/MoO<SUB><I>x</I></SUB>/Al configuration, the power conversion efficiency (PCE) was increased from 3.42 (without SubPc) to 3.59%. This improvement is mainly attributed to the enhanced open-circuit voltage from 0.62 to 0.64 V. When the Flory–Huggins interaction parameters were estimated from the solubility parameters through the contact angle measurement, it revealed that the interaction between SubPc and PC<SUB>71</SUB>BM is more attractive than that between SubPc and P3HT at the interface of P3HT:PC<SUB>71</SUB>BM/SubPc, through which charges are well transported from the active layer to the anode. This is supported by a decrease of the contact resistance from 5.49 (SubPc 0 nm) to 0.94 MΩ cm (SubPc 1 nm). The photoelectron spectra provide another evidence for the enhanced PCE, exhibiting that the 1 nm thick SubPc layer extracts more photoelectrons from the active layer than other thicknesses.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2011/aamick.2011.3.issue-11/am2009458/production/images/medium/am-2011-009458_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am2009458'>ACS Electronic Supporting Info</A></P>
Mobility of electrons and holes in an n-type organic semiconductor perylene diimide thin film
Kim, Jung Yong,Chung, In Jae,Lee, Changhee,Kim, Young Chul,Kim, Jai Kyeong,Yu, Jae-Woong Elsevier 2005 Current Applied Physics Vol.5 No.6
<P><B>Abstract</B></P><P><I>N</I>,<I>N</I>′-diphenylbutyl-3,4,9,10-perylenebiscarboximide (PTCDI-C4Ph) were characterized by optical and electrochemical methods. A device with an ITO/PTCDI-C4Ph (≈2μm)/Al structure was fabricated to measure mobility by time-of-flight techniques. This vacuum deposited organic layer was an amorphous state. Electrons were observed faster than holes. The electron and hole mobilities were 1.8×10<SUP>−4</SUP>cm<SUP>2</SUP>/Vs and 1.1×10<SUP>−4</SUP>cm<SUP>2</SUP>/Vs under the electric field of 500(V/cm)<SUP>1/2</SUP>, respectively. This result shows that this organic compound is a good candidate for an n-type conduction.</P>
Active Synchronizing Control of a Microgrid
Changhee Cho,Jin-Hong Jeon,Jong-Yul Kim,Soonman Kwon,Kyongyop Park,Sungshin Kim IEEE 2011 IEEE TRANSACTIONS ON POWER ELECTRONICS - Vol.26 No.12
<P>A microgrid is an aggregation of multiple distributed generators (DGs), such as renewable energy sources, conventional generators, and energy storage systems that provide both electric power and thermal energy. Typically, a microgrid operates in parallel with the main grid. However, there are cases in which a microgrid operates in an islanded mode, or in a disconnected state. Islanded microgrid can change its operational mode to grid-connected operation by reconnection to the grid, which is referred to as synchronization. Generally, a single machine simply synchronizes with the grid using a synchronizer. However, the synchronization of microgrids that operate with multiple DGs and loads cannot be controlled by a traditional synchronizer. It is needed to control multiple generators and energy storage systems in a coordinated way for the microgrid synchronization. This is not a simple problem, considering that a microgrid consists of various power electronics-based DGs as well as alternator-based generators that produce power together. This paper proposes an active synchronizing control scheme that adopts the network-based coordinated control of multiple DGs. From the simulation results using Simulink dynamic models, it is shown that the scheme provides the microgrid with a deterministic and reliable reconnection to the grid. The proposed method is verified by using the test cases with the experimental setup of a practical microgrid pilot plant.</P>
Kim, Jaehoon,Jung, Heeyoung,Song, Jiyun,Kim, Kyunghwan,Lee, Changhee American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.28
<P>Stable and robust open-circuit voltage (V-oc) is essential to achieve a long lifetime for polymer solar cells (PSCs). Here, we investigate the Voc burn-in loss mechanism on the basis of the analysis of electroluminescence quantum efficiency (EQE(EL)) and impedance measurements in amorphous PSCs, with an inverted structure having different electron transport layers (ETLs) of ZnO nanoparticles (NPs) and the sol gel processed ZnO layer. We found that both charge recombination and energetic disorder account for a substantial proportion of the Voc burn-in loss. Moreover, varying the ETL significantly affected the degree of V-oc burn in loss, although relative contribution of these two factors remained constant. To accurately extract charge recombination induced V-oc loss, we applied a novel yet effective method that relates the EQEEL of PSCs to charge recombination-induced V-oc loss. Additional analyses, including those focused on light intensity (P-light)-dependent V-oc and density of states, will provide an inclusive perspective on the degradation mechanism of V-oc and development of stable PSCs.</P>
Kim, Juneseob,Lee, Changhee,Choi, Hanshin,Jo, Hyungho,Kim, Hwijun Elsevier 2007 Materials science & engineering. properties, micro Vol.449 No.-
<P><B>Abstract</B></P><P>In this study, vacuum plasma spraying (VPS) was chosen for making Ni–Ti–Zr–Si–Sn bulk metallic glass (BMG) coating and the process parameters were optimized in view of phase composition of as-sprayed BMG overlay. When it comes to the phase evolution of BMG particle in thermal spraying process, the crystallization does occur by chemical instability and/or thermal instability. For the VPS process, the chemical instability such as in-flight particle oxidation can be neglected and thus the crystallization of BMG feedstock can be considered to result from the thermal instability. Actually, the crystalline phase fraction of the as-sprayed coatings was largely affected by the plasma gas composition which determines the plasma jet characteristics and also in-flight particle melting state. As the gas enthalpy is increased with the increase of hydrogen gas flow rate, number density of unmelted particle within the coating and crystalline phase fraction were consistently decreased. It implied that the phase composition of VPS BMG coating was largely dependent on the melting state of the impacting BMG particle.</P>
Kim, Jinwoo,Jeong, Jaewook,Cho, Hyun Duk,Lee, Changhee,Kim, Seul Ong,Kwon, Soon-Ki,Hong, Yongtaek Institute of Physics [etc.] 2009 Journal of Physics. D, Applied Physics Vol.42 No.11
<P>We report organic thin-film transistors (OTFTs) made by simple solution processes in an ambient air environment. Inkjet-printed silver electrodes were used for bottom-gate and bottom-contacted source/drain electrodes. A spin-coated cross-linked poly(4-vinylphenol) (PVP) and a spin-coated 6,13-<I>bis</I>(triisopropylsilylethynyl) pentacene (TIPS-pentacene) were used as a gate dielectric layer and an active layer, respectively. A high-boiling-point solvent was used for TIPS-pentacene and the resulting film showed stem-like morphology. X-ray diffraction (XRD) measurement showed the spin-coated active layer was well crystallized, showing the (0 0 1) plane. The reasonable mobility, on/off ratio and threshold voltage of the fabricated device, which are comparable to those of the previously reported TIPS-pentacene OTFT with gold electrodes, show that the printed silver electrodes worked successfully as gate and source/drain electrodes. Furthermore, the device showed a subthreshold slope of 0.61 V/dec in the linear region (<I>V</I><SUB>DS</SUB> = −5 V), which is the lowest value for spin-coated TIPS-pentacene TFT ever reported, and much lower than that of the thermally evaporated pentacene OTFTs. It is thought that the surface energy of the PVP dielectric layer is well matched with that of a well-ordered TIPS-pentacene (0 0 1) surface when a high-boiling-point solvent and a low-temperature drying process are used, thereby making good interface properties, and showing higher performances than those for pentacene TFT with the same structure.</P>