Youn Hwan Kim

Design and Fabrication of a Thin-Walled Free-Form Scaffold on the Basis of Medical Image Data and a 3D Printed Template: Its Potential Use in Bile Duct Regeneration

Three-dimensional (3D) printing, combined with medical imaging technologies, such as computed tomography and magnetic resonance imaging (MRI), has shown a great potential in patient-specific tissue regeneration. Here, we successfully fabricated an ultrathin tubular free-form structure with a wall thickness of several tens of micrometers that is capable of providing sufficient mechanical flexibility. Such a thin geometry cannot easily be achieved by 3D printing alone; therefore, it was realized through a serial combination of processes, including the 3D printing of a sacrificial template, the dip coating of the biomaterial, and the removal of the inner template. We demonstrated the feasibility of this novel tissue engineering construct by conducting bile duct surgery on rabbits. Moving from a rational design based on MRI data to a successful surgical procedure for reconstruction, we confirmed that the presented method of fabricating scaffolds has the potential for use in customized bile duct regeneration. In addition to the specific application presented here, the developed process and scaffold are expected to have universal applicability in other soft-tissue engineering fields, particularly those involving vascular, airway, and abdominal tubular tissues.

Synthesis of Conjugated Materials Based on Benzodithiophene - Benzothiadazole and Their Application of Organic Solar Cells

Electron acceptor-donor-acceptor type oligomers based on benzothiadiazole (BT) unit and a (4,8-bis((2-ethylhexyl)oxy)benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl) bis(trimethylstannane) (BDT) unit have been designed and prepared as electron-donating materials, which are 2,6-[5-(7-methyl-benzo[1,2,5]thiadiazol-4-yl)-thiophen-2-yl]-4,8-bis((2-ethylhexyl)oxy)benzo[1,2-b:4,5-b′]dithiophene) (BDT-TBT) and 2,6-[5′-(3′-hexyl-[2,2′]bithiophenyl-5-yl)-7-methyl-benzo[1,2,5]thiadiazole]-4,8-bis((2-ethylhexyl)oxy)benzo[1,2-b:4,5-b′]dithiophene) (BDT-THTBT), for Organic Solar Cells (OSCs) with PC71BM as electron-accepting materials. The HOMO energy level is elevated by the number of thiophene ring as a p-bridge, which lowers the band gap. Inverted-type organic solar cells (OSCs) with a configuration of ITO/ZnO/BDT-TBT (or BDT-THTBT):PC71BM/MoO3/Al are fabricated. OSC based on BDT-THTBT exhibits the highest power conversion efficiency (PCE) of 1.04% with the best Jsc of 4.20 mA/cm2.

Alcohol-soluble conjugated oligomers as the cathode interfacial layer in polymer solar cells

ABSTRACT Two easily accessible fluorene-based conjugated oligo-electrolytes (COEs) FTF- and FBF-NBr have been developed as the cathode interfacial layer (CIL) in inverted type polymer solar cells (iPSCs). CILsare interpretative to improving the power conversion efficiency (PCE) and long-term stability of the polymer photovoltaic cell that utilizes a high work function cathode. Compared to the reference devices without interlayer, FBF- and FTF-NBr exhibit significant improvements of the device parameters by reducing the work function of indium thin oxide (ITO). Conjugatedoligo-electrolytes in this work havelow lying HOMO levels −5.54 eV for FTF-NBr and −5.77 eV for FBF-NBr which are beneficial to hole-blocking ability. The iPSCs with FBF- and FTF-NBr as the inter layer at the cathode side were fabricated to investigate the effect of CIL on the photovoltaic properties. As a result, the PCE of 7.89% with FBF-NBr and 8.05% with FTF-NBr as the CIL has been achieved. Thus, the results indicate that fluorene-based COEs are potential CIL materials for the iPSCs.

New A-D-A type small molecules based on benzodithiophene derivative for organic solar cells

ABSTRACT A synthesized of acceptor-donor-acceptor (A-D-A) type oligomer based on benzodithiophene (BDT) as a donor (D) unit and phenylisoxazol (OX) as an acceptor (A) is to investigate the effect of combination between the strong electron donor and a strong electron acceptor. In addition, we introduce hexylthiophene (HT) ring as a π-bridge to extend the effective conjugation length and increase the solubility. Here we report the performance of 2,6-(4-(thiophen-2-yl)methylene)-3-phenylisoxazol-5(4H)-one)-4,8-bis((2-ethylhexyl)oxy)benzo[1,2-b:4,5-b′]dithiophene) (BDT-HTOX) employing as the electron donor in the inverted organic solar cells and PC71BM as the electron acceptor unit. UV-Vis absorption and electrochemical measurements investigated the optoelectronic properties that revealing the HUMO/LUMO level at −3.72 eV/−5.44 eV with an optical band gap of 1.72 eV for BDT-HTOX. Maximum power conversion efficiency based on BDT-HTOX is showed up to 0.80% with a short-circuit current density (Jsc) of –3.26 mA/cm2, Voc of 0.88 V, and fill factor (FF) of 27.9% using chlorobenzene as a solvent for solution processed organic solar cells.

A-π-D-π-A type oligomer based on carbazole and benzothiadiazole for organic solar cells

ABSTRACT An acceptor-donor-acceptor (A-p-D-p-A) type oligomer based on benzothiadiazole and 2,7 carbazole, 2,7-Bis(5-{7–2[-(4-decyloxy-phenyl)-vinyl]-benzo[1,2,5]thiadiazol-4-yl}-thiophen-2-yl)-9-(2-octyl-dodecyl)-9 H-carbazole (CzBT-DP), is synthesized by the Suzuki Coupling reaction. In addition, to extend the effective of conjugated length, we introduce thiophene (T) ring as a p-bridge and stilbene in the end of the conjugated chain. Optical, electrical and thermal properties and photovoltaic performances of CzBT-DP is systematically investigated. UV-vis absorption spectra and cyclic voltammograms (CV) reveal that HOMO/LUMO level of CzBT-DP is −5.37 eV/−3.38eV with an optical band gap of 1.99 eV, respectively, due to the addition of conjugated chain using stilbene compound system. The HOMO energies of CzBT-DP were calculated from the measured onset potential of oxidation by assuming the energy level of ferrocene (Fc) as −4.8 eV by CV. Addition of thiophene affects the HOMO level which makes CzBT-DP has high-lying HOMO level. Due to higher LUMO energy values above 0.3 eV than PC71 BM, CzBT-DP could be applied to BHJ OSCs as the donor [1]. Inverted type organic solar cells (OSCs) with a configuration of ITO/ZnO/CzBT-DP:PC71BM/MoO3/Al are fabricated. Figure 1 shows the current density-voltage (J-V) characteristics of the optimized BHJ OSCs based on CzBT-DP:PC71BM blend ratios from 3:2 to 3:6 (w/w). Maximum power conversion efficiency (PCE) is 0.64% with a short-circuit current density (Jsc) of 1.78 mA/cm2, Voc of 0.94 V, and fill factor (FF) of 38.3%. The best blend ratio between CzBT-DP and PC71BM having the best PCE appeared at 3:3 (w/w).

Synthesis and characterization conjugated oligomer based on phenothiazine derivative

ABSTRACT An acceptor-donor-acceptor (A-D-A) type oligomer based on benzothiadiazole and phenothiazine, 3,7-bis-[5-(7-methyl-benzo[1,2,5]thiadiazol-4-yl)-thiophen-2-yl]-10-(2-octyl-dodecyl)-10H-phenothiazine (PTBT), is synthesized by the Suzuki Coupling reaction. In addition, we introduce thiophene (T) ring as a π-bridge to extend the effective conjugation length. To investigate the effect of combination between strong electron donor and strong electron withdrawing on the diverse properties of conjugated oligomer on PTBT, optical and electrochemical properties are examined using UV-Vis absorption spectra and cyclic volatommograms (CV) that revealing HOMO/LUMO level at −5.36 eV/−3.18 eV with an optical band gap of 2.18 eV, respectively. Inverted-type organic solar cells (OSCs) with a configuration of ITO/ZnO/PTBT:PC71BM/MoO3/Al are fabricated. Maximum power conversion efficiency of the organic solar cells (OSCs) based on PTBT is showed up to 0.44% with a short-circuit current density (Jsc) of – 1.63 mA/cm2, Voc of 0.87 V, and fill factor (FF) of 30.9%.

Synthesis of low bandgap small molecules containing fluorinated benzothiadiazole and phenothiazine for photovoltaic applications

ABSTRACT A series of small molecules (SMs) containing fluorinated benzothiadiazole (BT) and phenothiazine (PT) were synthesized via the Suzuki coupling reaction. For exploring the effect of auxiliary electron-accepting moieties on the chemical structures, one or two fluorine atoms were selectively incorporated into the central electron-withdrawing BT unit of the non-fluorinated standard small molecule (BDP) to afford BDP-F and BDP-FF, respectively. Because of the favorable contributions of the fluorine atoms, the optimized inverted-type photovoltaic devices containing the SMs as active components exhibited improvement in PCE with increasing fluorine substitution, i.e., 0.49%, 0.54%, and 0.78% for BDP, BDP-F, and BDP-FF, respectively.

Cathode modification by the electrostatically self-assembled poly(4-vinylpyridine) derivative for enhancing the performance of polymer solar cells

ABSTRACT A non-conjugated polyelectrolyte, poly(4-vinyl N-ethyl pyridinium bromide) (PVPy-EtBr), is applied to polymer solar cells (PSCs) as a cathode buffer layer either inverted or conventional type polymer solar cells to improve the performances. The Kelvin probe microscopy measurement support the formation of favorable interface dipole at the cathode interface, indicating the reduction of a Schottky barrier for an electron collection from the active layer to the cathode treated with electrostatically self-assembly of PVPy-EtBr. Inverted type PSC with PVPy-EtBr as a cathode buffer layer demonstrate the power conversion efficiency (PCE) of 3.49%, which is better than the device without interlayer (PCE = 2.95%). Most increase in the PCE of the devices with interlayer is resulted from enhancement of the Jsc. This is due to that the reduction of a Schottky barrier at the cathode interface. Conventional type PSC with PVPy-EtBr (3.45%) at the cathode interface also exhibit better the PCE compared to that of the device without interlayer (2.88%).

Investigation of the effect of 2,6-pyridinedimethanol as the cathode buffer layer on the photovoltaic properties

ABSTRACT 2,6-pyridinedimethanol (Py-diOH) is applied to the cathode interlayer in inverted polymer solar cells (PSCs) based on the blend of PTB7:PC71BM. A layer of Py-diOH generates a favorable interface dipole at the cathode interface. The power conversion efficiency of the devices with the interlayer reaches up to 7.44% with a Jsc of 14.65 mA/cm2, a Voc of 0.71 V, and a FF of 67.9%, respectively The PCE of the device with Py-2OH is very similar to that of the device with ZnO as the electron collection layer. It is possible to obtain high efficiency PSCs without any high temperature heat treatment.