Sung-Hwan Han

Enhanced conversion efficiency in dye-sensitized solar cells based on hydrothermally synthesized TiO2-MWCNT nanocomposites.

A 50% enhancement in the conversion efficiency (4.9-7.37%) is realized in dye-sensitized solar cells using hydrothermally synthesized TiO(2)-multiwalled carbon nanotube (MWCNT) nanocomposites as compared to hydrothermally synthesized TiO(2) without MWCNT and Degussa P25. Several characterizations have been employed to reveal the nature of the modification imparted to the MWCNTs under hydrothermal processing conditions and the resulting TiO(2)-MWCNT conjugation through -COOH groups. Efficient charge transfer in the nanocomposite and efficient electron transport by MWCNT (significantly higher incident-photon-to-current conversion efficiency) are suggested to be the possible reasons for the enhancement.

Achievement of 4.51% conversion efficiency using ZnO recombination barrier layer in TiO2 based dye-sensitized solar cells

The authors report the use of chemically deposited ZnO recombination barrier layer for improved efficiency of TiO2 based dye-sensitized solar cells. The ZnO layers of different thicknesses were deposited on spin coated porous TiO2. The presence of ZnO over TiO2 was confirmed by x-ray diffraction, electron dispersive x-ray analysis, and supported by x-ray photoelectron spectroscopy, proved inherent energy barrier between the porous TiO2 electrode and lithium iodide electrolyte. They found that TiO2 based dye-sensitized solar cell with 30nm ZnO layer thickness showed 4.51% efficiency due to the formation of efficient recombination barrier at electrode/electrolyte interface. Further increase in ZnO barrier thickness may leak the electrons injected from the dye due to its low electron effective mass of 0.2me.

Enhanced charge collection and reduced recombination of CdS∕TiO2 quantum-dots sensitized solar cells in the presence of single-walled carbon nanotubes

This paper reports the modification of CdS∕TiO2 quantum-dot sensitized solar cells by using single-walled carbon nanotubes (SWCNTs) on indium-doped tin oxide (ITO) electrodes. The presence of the SWCNT layers on an ITO electrode increased the short-circuit current under the irradiation condition and also reduced the charge recombination process under the dark condition. The power conversion efficiency of CdS∕TiO2 on ITO increased 50.0% in the presence of SWCNTs due to the improved charge-collecting efficiency and reduced recombination.

Enhanced conversion efficiency in dye-sensitized solar cells based on ZnO bifunctional nanoflowers loaded with gold nanoparticles

The ZnO nanoflowers loaded with gold (Au) nanoparticles (NPs) are synthesized by a hydrothermal route using mixed precursors and controlled conditions. The dye-sensitized solar cells based on the ZnO nanoflowers with Au NPs show power conversion efficiency of 2.5%, which is considerably higher than that of ZnO nanoflowers without Au NPs. Detailed characterizations are performed, presented, and discussed.

A three-dimensional gold nanodendrite network porous structure and its application for an electrochemical sensing.

A three dimensional (3D) gold (Au) nanodendrite network porous structure constructed by a simple electrochemical synthetic method has been presented, and its utility for sensitive electrochemical measurement was demonstrated in this study. The 3D nanodendrite network porous structure was constructed on a platinum surface through electrodeposition of Au under the presence of hydrogen bubbles generated from the same surface. Iodide, used as a co-reagent, played an important role in the construction of the nanodendrite network by preventing continual growth of Au into larger agglomerates as well as inhibiting coalescence of neighboring nanodendrites. An electrochemical sensor incorporating the structure was built and used to detect As(III) in ultra low concentration range. For the purpose of comparison, bare gold and gold nanoparticle-incorporated electrodes were also prepared. With the use of 3D nanodendrite network porous structure, a much more sensitive detection of As(III) was possible due to its large surface area.

TiO2 nanotubes with a ZnO thin energy barrier for improved current efficiency of CdSe quantum-dot-sensitized solar cells

This paper reports the formation of a thin ZnO energy barrier between a CdSe quantum dot (Q dots) sensitizer and TiO2 nanotubes (TONTs) for improved current efficiency of Q dot-sensitized solar cells. The formation of a ZnO barrier between TONTs and the Q dot sensitizer increased the short-circuit current under illumination and also reduced the dark current in a dark environment. The power conversion efficiency of Q dot-sensitized TONT solar cells increased by 25.9% in the presence of the ZnO thin layer due to improved charge-collecting efficiency and reduced recombination.

Nanocrystalline CdS-water-soluble conjugated-polymers: High performance photoelectrochemical cells

Enhanced photoelectrochemical cell performance of nanocrystalline CdS-water-soluble conjugated-polymer sensitizers was demonstrated. The water-soluble polymers with quaternary pyridinium salts can be easily layered after dipping nanocrystalline CdS films in the aqueous polymer solution. The 2.37% energy conversion efficiency of CdS-poly(2-ethynyl-N-carboxypropylpyridiniumbromide) (LM 3) conjugated-polymer sensitizer was significantly higher than that of the bare (0.57%) and CdS-poly(2-ethynyl-N-aminopropylpyridiniumbromide) (LM 2) conjugated-polymer sensitizer (2.15%) under AM1.5 condition (80mW∕cm2).

Enhanced photovoltaic performance of Cu-based metal-organic frameworks sensitized solar cell by addition of carbon nanotubes

In the present work, TiO2 nanoparticle and multi-walled carbon nanotubes composite powder is prepared hydrothermally. After doctor blading the paste from composite powder, the resulted composite film is sensitized with Cu-based metal-organic frameworks using a layer-by-layer deposition technique and the film is characterized using FE-SEM, EDX, XRD, UV/Visible spectrophotometry and photoluminescence spectroscopy. The influence of the carbon nanotubes in photovoltaic performance is studied by constructing a Grätzel cell with I3−/I− redox couple containing electrolyte. The results demonstrate that the introduction of carbon nanotubes accelerates the electron transfer, and thereby enhances the photovoltaic performance of the cell with a nearly 60% increment in power conversion efficiency.

High‐Performance Air‐Stable Single‐Crystal Organic Nanowires Based on a New Indolocarbazole Derivative for Field‐Effect Transistors

A new indolocabazole derivative possessing an extended aromatic core and solubilizing long aliphatic chains effectively self-assembles and crystallizes within the nanoscale channels to form single-crystal nanowires via a direct printing method from an ink solution. Single-crystal organic nanowire transistor arrays based on the π-extended indolocarbazole derivative exhibit an excellent hole mobility of 1.5 cm² V⁻¹ s⁻¹ and outstanding environmental stability.

Hydrogel-Assisted Polyaniline Microfiber as Controllable Electrochemical Actuatable Supercapacitor

Flexible, controllable, and stable electrochemical supercapacitors serving as actuators at low operating voltage combining the advantages of the high power of the dielectric capacitors and the high specific energy of rechargeable batteries are important in artificial muscle technology, hybrid electric vehicles, and in short-term power sources for mobile electronic devices [Baughman, Science, 300, 268 (2003); Winter and Brodd, Chem. Rev. (Washington, D.C.), 104, 4245 (2004); Ebron, et al., Science, 311, 1580 (2006)]. High capacitance, a surprising 99% inner charge contribution and actuation in the hydrogel-assisted actuatable electrochemical supercapacitor (HAES) microfiber fabricated through wet spinning of a chitosan solution, followed by the in situ chemical polymerization of aniline was made possible through the perfect utilization of the large surface area provided by the nanostructured polyaniline grown inside as well as on the surface of the fiber. The HAES electrodes with an actuation strain of 0.33% showed 703 F/g specific capacitance in 1 M methane sulfonic acid, and more than 3000 cycles durability. The change in impedance as well as capacitance was achieved by the controlled strain as a function of applied stress, which can establish a direct relationship between the actuation strain and specific capacitance of electrochemical supercapacitors.