Hye-Na Kim

Enhanced Photovoltaic Properties of Nb2O5-Coated TiO2 3D Ordered Porous Electrodes in Dye-Sensitized Solar Cells

This paper describes the use of Nb₂O₅-coated TiO₂ 3D ordered porous electrodes in dye-sensitized solar cells. We employed bilayer inverse opal structures as a backbone of 3D porous structures, and the number of Nb₂O₅ coatings was controlled, determining the concentration of Nb₂O₅ coating. XPS measurements confirmed the formation of Nb₂O₅. The uniformity of the Nb₂O₅ coating was characterized by elemental mapping using SEM and TEM measurements. Photovoltaic measurement on dye-sensitized solar cells (DSSCs) that incorporated Nb₂O₅/TiO₂ inverse opal electrodes yielded a maximum efficiency of 7.23% for a 3.3 wt % Nb₂O₅ coating on a TiO₂ IO structure. The Nb₂O₅ significantly increased the short-circuit current density (J(SC)). Electrochemical impedance spectroscopy was used to measure the J(SC), revealing an enhanced electron injection upon deposition of the Nb₂O₅ coating.

Insertion mechanism of cell-penetrating peptides into supported phospholipid membranes revealed by X-ray and neutron reflection

X-Ray and neutron reflectivity measurements on systems composed of a 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) bilayer and transcription-activating-factor derived peptides (TDPs) have allowed us to determine the mechanism of membrane translocation. By monitoring the structural changes of the bilayers caused by the binding of TDPs while systemically varying temperature and TDP concentration, our results revealed the detailed molecular structures of the stepwise interactions that occurred during the translocation of TDP across the lipid bilayers. While little indication of membrane perturbation was observed at low TDP concentrations, we found that the TDP movement across the membrane induced defect formations in the membrane at higher TDP concentrations.

Surface modification of 2D/3D SU-8 patterns with a swelling–deswelling method

The grafting of PEG onto 2D and 3D SU-8 patterns with a swelling–deswelling approach has been demonstrated. The grafting density can be controlled by varying the amount of solvent used in the swelling. The grafting of the PEG-PPG-PEG block copolymers was confirmed directly with fluorescence characterization, and the control of the grafting density was assessed by performing contact-angle measurements. We also achieved the introduction of DNA molecules onto SU-8 patterns with the same approach. The swelling–deswelling approach is an inert and facile surface modification method, and can be extended to various SU-8 patterns for lab-on-a-chip applications and MEMS.

Characterization of charge transport properties of a 3D electrode for dye-sensitized solar cells.

Electron transport and recombination in three-dimensionally-ordered (3D-ordered) structure electrodes were investigated using intensity-modulated photocurrent and photovoltage spectroscopy. The surface-modified TiO2 inverse opal structure was applied as a 3D electrode. The morphology, crystalline structure and surface states of the 3D-ordered structure were characterized by SEM, TEM and XPS and compared to those of the conventional nanoparticulate TiO2 structure. The performance of the 3D electrode was also evaluated by comparing the transport time and recombination lifetime to those of the conventional electrodes. Remarkably, the recombination lifetime in inverse opal was found to be greater than in nanocrystalline TiO2 by 4.3-6.2 times, thus improving the electron collection efficiency by 10%. Comparing the photovoltaic performance, although the dye adsorption of the 3D-ordered porous electrode is lower, the electrode achieves a photocurrent density comparable to that of a nanoparticulate TiO2 electrode due to the higher light scattering as well as the higher collection efficiency.

Bottom-up Growth of Hierarchical Electrodes for Highly Efficient Dye-Sensitized Solar Cells

The nonconventional bottom-up growth of TiO2 was first demonstrated in the preparation of hierarchical TiO2 electrodes for use in highly efficient dye-sensitized solar cells. The simple immersion of a substrate in a precursor solution enabled the growth of TiO2 particulate films. Here, we have implemented a hierarchical growth strategy in which two stages of controlled growth yielded first macroscale TiO2 particles, followed by mesoscale TiO2 particles. We successfully fabricated electrode films up to 20 μm thick via a growth rate of 0.3 μm/min. The specific area of the electrodes was controlled via the deposition of mesoscale TiO2 particles. The deposited particles displayed a rutile phase with an average size of several tens of nanometers in diameter, as confirmed by XRD and high-resolution TEM imaging. After depositing the second layer of mesoscale TiO2 particles, the photocurrent density increased by a factor of 3. A maximum efficiency of 6.84% was obtained for the hierarchically structured TiO2 electrodes under 1 sun illumination. The hierarchical TiO2 electrodes were compared with macroporous TiO2 electrodes, revealing that the higher photocurrent density could be attributed to a longer electron recombination lifetime and a high specific area. The longer recombination lifetime was supported by the presence of fewer defective TiO2 surfaces, as confirmed by the XPS spectrum.