Woongsik Jang

Electrophysiological study for comparing the effect of biological activity between type A botulinum toxins in rat gastrocnemius muscle

Background: New cosmetic applications and products based on the effects of botulinum toxin (BTX) treatment have stimulated demand for this class of natural compounds. This demand generates the need for appropriate standardized protocols to test and compare the effectiveness of new BTX preparations. Objectives: Based on the previously described electrophysiological methods, we measured and compared the inhibitory effects of two BTX type A (BTX-A) preparations on neuromuscular transmission through split-body test. Methods: The effectiveness was evaluated in terms of the compound muscle action potential (CMAP) and conduction velocity after BTX-A injection. We used a split-body method to compare two different BTX-As in the rat. Results: Based on the changes in the CMAP, the two different BTX-As induced paralytic effect on the rat tibialis anterior muscle. However, the two different BTX-A preparations did not differ significantly in effectiveness and did not induce a delay in conduction velocity. Conclusions: The new BTX-A preparation used in this electrophysiological study had similar effect compared with the previously marketed BTX-A.[AQ: Please approve the edits made to the sentence “The new BTX-A preparation…”) We propose that a split-body electrophysiological protocol will be useful in establishing the comparative effectiveness of new BTX products.

Morphology fixing agent for [6,6]-phenyl C61-butyric acid methyl ester (PC60BM) in planar-type perovskite solar cells for enhanced stability

Here, we report that the delamination of [6,6]-phenyl C61-butyric acid methyl ester (PC60BM) from the CH3NH3PbI3 (MAPbI3) layer is a critical reason for the degradation of inverted perovskite solar cells (PSCs). In this work, an ∼10 nm-thick titanium oxide (TiOx) layer can function as a morphology-fixing agent for preventing PC60BM delamination, which in turn induces greatly improved long-term stability of the PSCs. In addition, the devices with the TiOx layer exhibited increased open circuit voltages, current densities, and fill factors, which correspond to improved initial device efficiency. Surface morphology changes of the PC60BM layer on the MAPbI3 layer during long-term operation of PSCs were confirmed by SEM and AFM, and were also found to be correlated with various electrical properties of the devices such as the hole mobility and charge generation and extraction efficiencies from the space-charge-limited current (SCLC) measurements and Jph versus Vint characterizations.

Vacuum-process-based dry transfer of active layer with solvent additive for efficient organic photovoltaic devices

Stamping transfer process for fabricating organic electronics has recently been demonstrated to improve device performance because it allows the control of morphology, patterning, and transfer of various materials. However, it still has issues related to reproducibility because complex solvent conditions, that is, several active layers consisting of solvent additives or mixtures used for improving morphology, unfavorably affect the film transfer. To transfer uniform thin films, poly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl}):[6,6]-phenyl-C71-butyric acid methyl ester (PTB7:PC71BM)-based organic photovoltaic cells were fabricated in this study by utilizing the optimized surface energy of the hydrophilic 2-hydroxyethyl methacrylate–polyurethane acrylate stamp. Upon application of vacuum treatment based on dry transfer, a bulk-heterojunction (BHJ) layer with the solvent additive, 1,8-diiodooctane, was completely transferred onto a poly-(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) layer without any change in its domain distribution and composition. Consequently, BHJ devices fabricated by stamping transfer showed power conversion efficiency comparable to those of devices fabricated by spin-coating. We also observed significant improvement in long-term stability of the PTB7:PC71BM-based photovoltaic cells fabricated by stamping transfer under dry conditions.

Dry-Stamping-Transferred PC71BM Charge Transport Layer via an Interface-Controlled Polyurethane Acrylate Mold Film for Efficient Planar-Type Perovskite Solar Cells

The study of interlayers is important to enhance the performance of inverted perovskite solar cells (PSCs) because interlayers in PSCs align energy levels and improve charge transport. However, previous research into applying interlayers for PSCs has focused only on wet-coated methods, such as spin coating, to form the interlayer. Here, we fabricated planar-type PSCs deposited with a 6,6-phenyl-C71 butyric acid methyl ester (PC71BM) layer onto a CH3NH3PbI3 (MAPbI3) layer by stamping transfer through a relatively dry process condition. We demonstrated the effects of a stamping-transferred PC71BM layer using polyurethane acrylate (PUA), the surface energy of which was modified by 2-hydroxyethyl methacrylate (HEMA) to increase the transfer reproducibility. In PSCs with a stamping-transferred PC71BM layer, we observed an enhanced JSC and a comparable power conversion efficiency (PCE), which were caused by an enhanced coverage of the electron transport layer onto the MAPbI3 layer with preserved crystallinity, which occurs owing to improved electron mobility and exciton dissociation. The optimized device PCE through the dry-transferred PC71BM exhibited a JSC, fill factor, and PCE of 21.65 mA/cm2, 76.0%, and 15.46%, respectively. Moreover, morphological analysis and electrical measurements confirmed the improved durability of dry-stamping-transferred PSCs.

Counterbalancing of morphology and conductivity of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate based flexible devices

The importance of conductive polymer electrodes with a balance between the morphology and electrical conductivity for flexible organic photovoltaic properties has been demonstrated. Highly transparent PEDOT:PSS anodes with controlled conductivity and surface properties were realized by insertion of dimethyl sulfoxide (DMSO) and a fluorosurfactant (Zonyl) as efficient additives and used for flexible organic photovoltaic cells (OPVs) which are based on a bulk-heterojunction of polythieno[3,4-b]-thiophene-co-benzodithiophene (PTB7):[6,6]phenyl-C71-butyric acid methyl ester (PC71BM). We investigated the correlation between the electrical properties of PEDOT:PSS electrodes and their influences on the surface morphology of the active materials (PTB7:PC71BM). When the device was prepared from the PEDOT:PSS layer functioning as an anode of OPV through an optimized ratio of 5 vol% of DMSO and 0.1 wt% of fluorosurfactant, the devices exhibited improved fill factor (FF) due to the enhanced coverage of PEDOT:PSS films. These results correlate with reduced photoluminescence and increased charge extraction as seen through Raman spectroscopy and electrical analysis, respectively. The conductive polymer electrode with the balance between the morphology and electrical conductivity can be a useful replacement for brittle electrodes such as those made of indium tin oxide (ITO) as they are more resistant to cracking and bending conditions, which will contribute to the long-term operation of flexible devices.

Alignment of Cascaded Band-Gap via PCBM/ZnO Hybrid Interlayers for Efficient Perovskite Photovoltaic Cells

In this study, we investigated methylammonium lead iodide (MAPbI3)-perovskite solar cells (PSCs) with hybrid PC70BM/ZnO interlayers. The pristine device which had a PC70BM electron transport layer sandwiched between ITO/PEDOT:PSS/MAPbI3 and TiOx/Al electrodes exhibited PCE of 12.72% with a VOC of 0.98 V, Jsc of 18.41 mA/cm2, and FF of 71%. The new device with hybrid PC70BM/ZnO interlayers exhibited higher PCE of 14.17% with a VOC of 0.98 V, JSC of 20.08 mA/cm2, and FF of 72% due to the incorporation of ZnO nanoparticles in PC70BM electron transport layer (ETL) with high electron mobility and cascade band gap alignment. Here, we demonstrated that lower photoluminescence (PL) intensity of the device with hybrid interlayers could improve the JSC value of perovskite solar cells due to enhanced charge-generation efficiency. Contact resistance can be reduced by mixing ZnO nanoparticles with PC70BM electron transport layer without additional ZnO layer insertion.

Nanopatterned bulk-heterojunction photovoltaic cells using polyurethane acrylate (PUA) film replica of colloidal crystal arrays via stamping transfer process

Bulk heterojunction (BHJ) films with nanopattern structure have been fabricated using a stamping transfer process with polyurethane acrylate (PUA) replica film based on 3-dimensional colloidal crystals. The uniformly arrayed nanostructure of the PUA film was investigated by SEM analysis. Compared to the organic photovoltaic cells wtih plain BHJ of poly(3-hexylthiophene-2,5-diyl) (P3HT) and indene-C60 bisadduct (ICBA), the device from the nanopatterned BHJ exhibit improved E-field distribution intensity, as assessed using a finite-difference time-domain (FDTD) method. The current density (JSC) and power conversion efficiency (PCE) of the device were respectively increased by up to 27% and 20% due to the enhanced interfacial contact area and plasmonic effect, which can brought about effective light harvesting between the BHJ active layer and cathode. Through a simple low-temperature transfer process using a PUA mold, we can fabricate reproducible nanopatterned BHJ devices that have improved light absorption within the active layer of the devices.