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Kim, Min Je,Park, Jae Hoon,Kang, Boseok,Kim, Dongjin,Jung, A-Ra,Yang, Jeehye,Kang, Moon Sung,Lee, Dong Yun,Cho, Kilwon,Kim, Hyunjung,Kim, BongSoo,Cho, Jeong Ho American Chemical Society 2016 The Journal of Physical Chemistry Part C Vol.120 No.26
<P>The performances of organic thin film transistors (OTFTs) produced by polymer solution casting are tightly correlated with the morphology and chain-ordering of semiconducting polymer layers, which depends on the processing conditions applied. The slow evaporation of a high boiling point (bp) solvent permits sufficient time for the assembly of polymer chains during the process, resulting in improving the film crystallinity and inducing favorable polymer chain orientations for charge transport. The use of high bp solvents, however, often results in dewetting of thin films formed on hydrophobic surfaces, such as the commonly used octadecyltrichlorosilane (ODTS)-treated SiO2 gate dielectric. Dewetting hampers the formation of uniform and highly crystalline semiconducting active channel layers. In this manuscript, we demonstrated the formation of highly crystalline dithienothienyl diketopyrrolopyrrole (TT-DPP)-based polymer films using a flow-coating method to enable the fabrication of ambipolar transistors and inverters. Importantly, unlike conventional spin-coating methods, the flow-coating method allowed us to use high bp solvents, even on a hydrophobic surface, and minimized the polymer solution waste. The crystalline orientations of the TT-DPP-based polymers were tuned depending on the solvent used (four different bp solvents were tested) and the employment of a thermal annealing step. The use of high bp solvents and thermal annealing of the polymer films significantly enhanced the crystalline microstructures in the flow-coated films, resulting in considerable carrier mobility increase in the OTFTs compared to the spin-coated films. Our simple, inexpensive, and scalable flow-coating method, for the first time employed in printing semiconducting polymers, presents a significant step toward optimizing the electrical performances of organic ambipolar transistors through organic semiconducting layer film crystallinity engineering.</P>
Kim, Min Je,Jung, A-Ra,Lee, Myeongjae,Kim, Dongjin,Ro, Suhee,Jin, Seon-Mi,Nguyen, Hieu Dinh,Yang, Jeehye,Lee, Kyung-Koo,Lee, Eunji,Kang, Moon Sung,Kim, Hyunjung,Choi, Jong-Ho,Kim, BongSoo,Cho, Jeong H American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.46
<P>We report high-performance top-gate bottom-contact flexible polymer field-effect transistors (FETs) fabricated by flow-coating diketopyrrolopyrrole (DPP)-based and naphthalene diimide (NDI)-based polymers (P(DPP2DT-T2), P(DPP2DT-TT), P(DPP2DT-DTT), P(NDI2OD-T2), P(NDI2OD-F2T2), and P(NDI2OD-Se2)) as semiconducting channel materials. All of the polymers displayed good FET characteristics with on/off current ratios exceeding 10(7). The highest hole mobility of 1.51 cm(2) V-1 s(-1) and the highest electron mobility of 0.85 cm(2) V-1 s(-1) were obtained from the P(DPP2DT-T2) and P(NDI2OD-Se2) polymer FETs, respectively. The impacts of the polymer structures on the FET performance are well-explained by the interplay between the crystallinity, the tendency of the polymer backbone to adopt an edge-on orientation, and the interconnectivity of polymer fibrils in the film state. Additionally, we demonstrated that all of the flexible polymer-based FETs were highly resistant to tensile stress, with negligible changes in their carrier mobilities and on/off ratios after a bending test. Conclusively, these high-performance, flexible, and durable FETs demonstrate the potential of semiconducting conjugated polymers for use in flexible electronic applications.</P>
Kim, Jihwan,Kim, Bum-Kyu,Kim, Hong-Seok,Hwang, Ahreum,Kim, Bongsoo,Doh, Yong-Joo American Chemical Society 2017 NANO LETTERS Vol.17 No.11
<P>We report on the fabrication and electrical transport properties of superconducting junctions made of beta-Ag2Se topological insulator (Tl) nanowires in contact with Al superconducting electrodes. The temperature dependence of the critical current indicates that the superconducting junction belongs to a short and diffusive junction regime. As a characteristic feature of the narrow junction, the critical current decreases monotonously with increasing magnetic field. The stochastic distribution of the switching current exhibits the macroscopic quantum tunneling behavior, which is robust up to T = 0.8 K. Our observations indicate that the Tl nanowire-based Josephson junctions can be a promising building block for the development of nanohybrid superconducting quantum bits.</P>
Kim, Beom Joon,Lee, Hyo-Sang,Lee, Joong Seok,Cho, Sanghyeok,Kim, Hyunjung,Son, Hae Jung,Kim, Honggon,Ko, Min Jae,Park, Sungnam,Kang, Moon Sung,Oh, Se Young,Kim, BongSoo,Cho, Jeong Ho American Chemical Society 2013 JOURNAL OF PHYSICAL CHEMISTRY C - Vol.117 No.22
<P>We characterized the electrical properties of ambipolar polymer field-effect transistors (PFETs) based on the low-band-gap polymer, pNAPDO-DPP-EH. The polymer consisted of electron-rich 2,6-di(thienyl)naphthalene units with decyloxy chains (NAPDO) and electron-deficient diketopyrrolopyrrole units with 2-ethylhexyl chains (DPP-EH). The as-spun pNAPDO-DPP-EH PFET device exhibited ambipolar transport properties with a hole mobility of 3.64 × 10<SUP>–3</SUP> cm<SUP>2</SUP>/(V s) and an electron mobility of 0.37 × 10<SUP>–3</SUP> cm<SUP>2</SUP>/(V s). Thermal annealing of the polymer film resulted in a dramatic increase in the carrier mobility. Annealing at 200 °C yielded hole and electron mobilities of 0.078 and 0.002 cm<SUP>2</SUP>/(V s), respectively. The mechanism by which the mobility had improved was investigated via grazing incidence X-ray diffraction studies, atomic force microscopy, and temperature-dependent transport measurements. These results indicated that thermal annealing improved the polymer film crystallinity and promoted the formation of a longer-range lamellar structure that lowered the thermal activation energy for charge hopping. Thermal annealing, moreover, reduced charge trapping in the films and thus improved the electrical stability of the PFET device. This work underscores the fact that long-range ordering in a crystalline polymer is of great importance for efficient charge transport and high electrical stability.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2013/jpccck.2013.117.issue-22/jp400664r/production/images/medium/jp-2013-00664r_0010.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp400664r'>ACS Electronic Supporting Info</A></P>
Kim, Minjin,Kim, Jihwan,Lee, In-Ho,Han, Woo Hyun,Park, Yun Chang,Kim, Woo Youn,Kim, Bongsoo,Suh, Junho Royal Society of Chemistry 2019 Nanoscale Vol.11 No.12
<P>We report a ternary silver chalcogenide, Ag2Se0.5Te0.5, as a new topological material with improved quantum transport properties. Single-crystalline nanostructures of ternary silver chalcogenides Ag2SexTe1−x are synthesized with a tunable chemical composition <I>via</I> the chemical vapor transport method. Quantum transport studies reveal that Ag2Se0.5Te0.5 nanowires present topological surface states with higher electron mobility and longer mean free path compared to binary Ag-chalcogenides. First-principles calculations also indicate that Ag2Se0.5Te0.5 is a topological insulator, and the observed enhancement in transport properties could imply reduced bulk carrier contribution in the new ternary silver chalcogenide.</P>
Kim, Ji-Hoon,Song, Chang Eun,Shin, Nara,Kang, Hyunbum,Wood, Sebastian,Kang, In-Nam,Kim, Bumjoon J.,Kim, BongSoo,Kim, Ji-Seon,Shin, Won Suk,Hwang, Do-Hoon American Chemical Society 2013 ACS APPLIED MATERIALS & INTERFACES Vol.5 No.24
<P>Two semiconducting conjugated polymers were synthesized via Stille polymerization. The structures combined unsubstituted or (triisopropylsilyl)ethynyl (TIPS)-substituted 2,6-bis(trimethylstannyl)benzo[1,2-<I>b</I>:4.5-<I>b</I>′]dithiophene (BDT) as a donor unit and benzotriazole with a symmetrically branched alkyl side chain (DTBTz) as an acceptor unit. We investigated the effects of the different BDT moieties on the optical, electrochemical, and photovoltaic properties of the polymers and the film crystallinities and carrier mobilities. The optical-band-gap energies were measured to be 1.97 and 1.95 eV for PBDT-DTBTz and PTIPSBDT-DTBTz, respectively. Bulk heterojunction photovoltaic devices were fabricated and power conversion efficiencies of 5.5% and 2.9% were found for the PTIPSBDT-DTBTz- and PBDT-DTBTz-based devices, respectively. This difference was explained by the more optimal morphology and higher carrier mobility in the PTIPSBDT-DTBTz-based devices. This work demonstrates that, under the appropriate processing conditions, TIPS groups can change the molecular ordering and lower the highest occupied molecular orbital level, providing the potential for improved solar cell performance.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2013/aamick.2013.5.issue-24/am401926h/production/images/medium/am-2013-01926h_0013.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am401926h'>ACS Electronic Supporting Info</A></P>
Kim, Jae-Yup,Kim, Jin Young,Lee, Doh-Kwon,Kim, BongSoo,Kim, Honggon,Ko, Min Jae American Chemical Society 2012 The Journal of Physical Chemistry Part C Vol.116 No.43
<P>The photovoltaic performance of dye-sensitized solar cells (DSSCs) employing SnO<SUB>2</SUB> electrodes was investigated while increasing the content of 4-<I>tert</I>-butylpyridine (TBP) in the conventional liquid-type electrolyte. As the added TBP content increased, the open circuit voltage (<I>V</I><SUB>oc</SUB>) and conversion efficiency were highly enhanced while the short circuit current (<I>J</I><SUB>sc</SUB>) was not much affected. With the electrolyte of 2.0 M TBP, the <I>V</I><SUB>oc</SUB> and conversion efficiency were increased by 26 and 33%, respectively, compared with the conventional electrolyte (0.5 M TBP). The electrochemical impedance spectra revealed that the enhancement of <I>V</I><SUB>oc</SUB> resulted from the negative shift of the SnO<SUB>2</SUB> conduction band potential and the increase in resistance of electron recombination by 1 order of magnitude. It is noteworthy that the optimized concentration of TBP for the SnO<SUB>2</SUB> electrode is greatly larger than that for the TiO<SUB>2</SUB> electrode. This may be due to the much faster electron recombination rate and more positive conduction band potential of the SnO<SUB>2</SUB> electrode. The SnO<SUB>2</SUB> electrode modified with TiO<SUB>2</SUB> shell showed only slightly enhanced performance due to the similar effects of shell layer and those of the TBP. In contrast to the SnO<SUB>2</SUB>, TiO<SUB>2</SUB> electrodes did not show performance enhancement with the electrolyte of TBP concentration larger than 0.5 M. The impedance spectra of symmetric dummy cells employing Pt counter electrodes indicated that the catalytic effect of Pt was deteriorated, and the resistance of electrolyte diffusion was increased by the higher concentration of TBP. This brings up the need for development of a counter electrode that TBP is not easily adsorbed on, and alternative additives to TBP which are not highly viscous.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2012/jpccck.2012.116.issue-43/jp307783q/production/images/medium/jp-2012-07783q_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp307783q'>ACS Electronic Supporting Info</A></P>