Publications by authors named "Hyo-Joong Lee"

Recently, halide perovskites have been widely explored for high-efficiency photocatalysis or photoelectrochemical (PEC) cells. Here, in order to make an efficient photoanode electrode for the degradation of pollutants, concretely 2-mercaptobenzothiazole (MBT), nanoscale cesium lead bromide (CsPbBr) perovskite was directly formed on the surface of mesoporous titanium dioxide (meso-TiO) film using a two-step spin-coating process. This photoelectrode recorded a photocurrent of up to 3.

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Zinc sulfide (ZnS) was deposited onto the surface of mesoporous TiO film by a typical successive ionic layer adsorption and reaction (SILAR) process. By inducing a spontaneous cation exchange between ZnS and a target cation (Pb, Cu, Ag, or Bi) dissolved in a chemical bath when they are in contact, it was demonstrated successfully that white translucent ZnS on the substrate could be changed to new brown-colored metal chalcogenides and the amount of ZnS deposited originally by different conditions could be compared in a qualitative way with the degree of color change. By utilizing this simple but effective process, the evolution of a well-known ZnS passivation layer prepared from different chemical baths in quantum dot (QD)-sensitized solar cells could be tracked visually by checking the degree of color change of TiO/ZnS electrodes after the induced specific cation exchange.

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A general and straightforward way of preparing few-nanometer-sized well-separated MAPbI Br (MA=methylammonium) perovskite photosensitizers on the surface of an approximately 1 μm thick mesoporous TiO photoanode was suggested through a two-step sequential deposition of low-concentrated lead halides (0.10-0.30 m PbI or PbBr ) and methylammonium iodide/bromide (MAI/MABr).

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Planar perovskite solar cells using low-temperature atomic layer deposition (ALD) of the SnO electron transporting layer (ETL), with excellent electron extraction and hole-blocking ability, offer significant advantages compared with high-temperature deposition methods. The optical, chemical, and electrical properties of the ALD SnO layer and its influence on the device performance are investigated. It is found that surface passivation of SnO is essential to reduce charge recombination at the perovskite and ETL interface and show that the fabricated planar perovskite solar cells exhibit high reproducibility, stability, and power conversion efficiency of 20%.

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A nanoscale composite sensitizer composed of CuS and CdS quantum dots (QDs) was prepared by a simple but effective layer-by-layer reaction between a metal cation (Cu(2+) or Cd(2+)) and a sulfide anion (S(2-)). The as-prepared composite CuS/CdS QD sensitizer displayed an enhanced photon-to-current conversion over the sensitizing range of the visible spectrum compared to the counterpart of the pure CdS sensitizer. At the optimized ratio of the deposited amounts of CuS and CdS, the best CuS/CdS-sensitized mesoporous TiO2 cell with a polysulfide electrolyte showed an overall power conversion efficiency of 3.

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The aim of the present study was to prepare the particulate taste-masking system to mask the bitter taste of sildenafil citrate (SC), a well-known phosphodiesterase-5 inhibitor used for erectile dysfunction (ED) and pulmonary artery hypertension (PAH). It was evaluated for the taste masking efficiency by the in vitro measurement using electronic tongue (e-tongue) system and the in vivo human panel sensory test. Microcapsules were prepared by microencapsulation with a gastro-soluble polymer, Eudragit(®) E100 (E100), using a spray drying technique at four different weight ratios (2:1, 1:1, 1:2, and 1:3).

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Layer cake: Multilayered CdSe quantum dot (QD) sensitizers are layer-by-layer assembled onto ZnO nanowires by making use of electrostatic interactions to study the effect of the layer number on the photovoltaic properties. The photovoltaic performance of QD-sensitized solar cells critically depends on this number as a result of the balance between light-harvesting efficiency and carrier-recombination probability.

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A multilayer of CdSe quantum dots (QDs) was prepared on the mesoporous surface of a nanoparticulate TiO(2) film by a layer-by-layer (LBL) assembly using the electrostatic interaction of the oppositely charged QD surface for application as a sensitizer in QD-sensitized TiO(2) solar cells. To maximize the absorption of incident light and the generation of excitons by CdSe QDs within a fixed thickness of TiO(2) film, the experimental conditions of QD deposition were optimized by controlling the concentration of salt added into the QD-dissolved solutions and repeating the LBL deposition a few times. A proper concentration of salt was found to be critical in providing a deep penetration of QDs into the mesopore, thus leading to a dense and uniform distribution throughout the whole TiO(2) matrix while anchoring the oppositely charged QDs alternately in a controllable way.

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The assembly of reduced graphene oxide (rGO) and fullerene (C(60)) into hybrid (rGO/C(60)) wires was successfully performed by employing the liquid-liquid interfacial precipitation method. The rGO sheets spontaneously wrapped C(60) wires through the π-π interaction between rGO and C(60). Structural characterization of the rGO/C(60) wires was carried out by using UV/visible spectroscopy, scanning electron microscopy, and transmission electron microscopy.

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A novel multifunctional conjugated polymer (RCP-1) composed of an electron-donating backbone (carbazole) and an electron-accepting side chain (cyanoacetic acid) connected through conjugated vinylene and terthiophene has been synthesized and tested as a photosensitizer in two major molecule-based solar cells, namely dye sensitized solar cells (DSSCs) and organic photovoltaic cells (OPVs). Promising initial results on overall power conversion efficiencies of 4.11% and 1.

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Novel quinoxaline-based organic sensitizers using vertical (RC-21) and horizontal (RC-22) conjugation between an electron-donating triphenylamine unit and electron-accepting quinoxaline unit have been synthesized and used for dye-sensitized solar cells (DSSCs), leading to the relatively high power conversion efficiencies of 3.30 and 5.56% for RC-21 and RC-22, respectively.

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Redox couples based on cobalt complexes were found to be effective in regenerating both inorganic CdSe quantum dot- and organic dye-sensitizers. The hybrid sensitizer composed of CdSe QD and ruthenium sensitizer (Z907Na) dye showed a maximum power conversion efficiency of 4.76% on using cobalt(o-phen)(3)(2+/3+) as a common redox mediator.

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[Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)] (PEDOT:PSS, Baytron P) composite films were prepared under various conditions and their conductivities were studied by the current-sensing atomic force microscopy (CS-AFM) technique. Topographic and current images of pristine and additive-treated PEDOT:PSS as well as electrochemically synthesized PEDOT films were obtained in nanoscale using the CS-AFM. The as-prepared pristine PEDOT:PSS films showed a low population of conductive spots isolated by large insulating regions; both their population and the conductivities increased upon addition of a few additives to the PEDOT:PSS solution before spin-coating.

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Metal sulfide (PbS and CdS) quantum dots (QDs) were prepared over mesoporous TiO2 films by improved successive ionic layer adsorption and reaction (SILAR) processes. The as-prepared QD-sensitized electrodes were combined with a cobalt complex redox couple [Co(o-phen)3]2+/3+ to make a regenerative liquid-type photovoltaic cell. The optimized PbS QD-sensitized solar cells exhibited promising incident photon-to-current conversion efficiency (IPCE) of over 50% and an overall conversion efficiency of 2% at 0.

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Electrical and morphological properties of polypyrrole (PPy) films were studied during and after their electrochemical growth under various experimental conditions on a nanometer scale using a current-sensing atomic force microscope (CS-AFM). Of acetonitrile (ACN) solutions containing various amounts of water, one that contained 1.0% water produced the best quality films in their electrical and morphological properties in terms of homogeneities.

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