Sang-Won Park

Bio: Sang-Won Park is an academic researcher from Sungkyunkwan University. The author has contributed to research in topics: Nitric oxide synthase & Copolyester. The author has an hindex of 11, co-authored 25 publications receiving 3009 citations. Previous affiliations of Sang-Won Park include Jaseng Hospital of Korean Medicine.

6.5% efficient perovskite quantum-dot-sensitized solar cell

Abstract: Highly efficient quantum-dot-sensitized solar cell is fabricated using ca. 2–3 nm sized perovskite (CH3NH3)PbI3 nanocrystal. Spin-coating of the equimolar mixture of CH3NH3I and PbI2 in γ-butyrolactone solution (perovskite precursor solution) leads to (CH3NH3)PbI3 quantum dots (QDs) on nanocrystalline TiO2 surface. By electrochemical junction with iodide/iodine based redox electrolyte, perovskite QD-sensitized 3.6 μm-thick TiO2 film shows maximum external quantum efficiency (EQE) of 78.6% at 530 nm and solar-to-electrical conversion efficiency of 6.54% at AM 1.5G 1 sun intensity (100 mW cm−2), which is by far the highest efficiency among the reported inorganic quantum dot sensitizers.

Protective mechanism of glycyrrhizin on acute liver injury induced by carbon tetrachloride in mice.

Abstract: Glycyrrhizin is the major active component extracted from licorice (Glycyrrhiza glabra) roots, one of the most widely used herbal preparations for the treatment of liver disorders. This study evaluated the potential beneficial effect of glycyrrhizin in a mouse model of carbon tetrachloride (CCl(4))-induced liver injury. The mice were treated intraperitoneally with CCl(4) (0.5 ml/kg). They received glycyrrhizin (50, 100, 200, 400 mg/kg) 24 h and 0.5 h before and 4 h after administering CCl(4). The serum activities of aminotransferase and the hepatic level of malondialdehyde were significantly higher 24 h after the CCl(4) treatment, while the concentration of reduced glutathione was lower. These changes were attenuated by glycyrrhizin. CCl(4) increased the level of circulating tumor necrosis factor-alpha markedly, which was reduced by glycyrrhizin. The levels of hepatic inducible nitric oxide synthase, cyclooxygenase-2, and heme oxygenase-1 protein expression were markedly higher after the CCl(4) treatment. Glycyrrhizin diminished these alterations for inducible nitric oxide and cyclooxygenase-2 but the protein expression of heme oxygenase-1 was further elevated by the treatment of glycyrrhizin. CCl(4) increased the level of tumor necrosis factor-alpha, inducible nitric oxide synthase, cyclooxygenase-2, and heme oxygenase-1 mRNA expressions. The mRNA expression of heme oxygenase-1 was augmented by the glycyrrhizin treatment, while glycyrrhizin attenuated the increase in tumor necrosis factor-alpha, inducible nitric oxide synthase, and cyclooxygenase-2 mRNA expressions. These results suggest that glycyrrhizin alleviates CCl(4)-induced liver injury, and this protection is likely due to the induction of heme oxygenase-1 and the downregulation of proinflammatory mediators.

Effect of GCSB-5, a Herbal Formulation, on Monosodium Iodoacetate-Induced Osteoarthritis in Rats.

Abstract: Therapeutic effects of GCSB-5 on osteoarthritis were measured by the amount of glycosaminoglycan in rabbit articular cartilage explants in vitro, in experimental osteoarthritis induced by intra-articular injection of monoiodoacetate in rats in vivo. GCSB-5 was orally administered for 28 days. In vitro, GCSB-5 inhibited proteoglycan degradation. GCSB-5 significantly suppressed the histological changes in monoiodoacetate-induced osteoarthritis. Matrix metalloproteinase (MMP) activity, as well as, the levels of serum tumor necrosis factor-α, cyclooxygenase-2, inducible nitric oxide synthase protein, and mRNA expressions were attenuated by GCSB-5, whereas the level of interleukin-10 was potentiated. By GCSB-5, the level of nuclear factor-κB p65 protein expression was significantly attenuated but, on the other hand, the level of inhibitor of κB-α protein expression was increased. These results indicate that GCSB-5 is a potential therapeutic agent for the protection of articular cartilage against progression of osteoarthritis through inhibition of MMPs activity, inflammatory mediators, and NF-κB activation.

Protective Effects of Human Placenta Extract on Cartilage Degradation in Experimental Osteoarthritis

Abstract: This study investigated the effect of human placenta extract (HPE) on cartilage degradation in vitro MG-63 cells, articular cartilage explants, and in vivo monoiodoacetate (MIA)-induced osteoarthritis (OA). Matrix metalloproteinase (MMP)-2 activity was measured in HPE-treated osteoblastic MG-63 cells. Articular cartilage explants in rabbit were cultured, and the degree of proteoglycan (PG) degradation was assessed by measuring the amount of glycosaminoglycan (GAG) released into the culture medium. Experimental osteoarthritis was induced by intra-articular injection of 3 mg MIA in rats. Beginning 14 d post-MIA injection, HPE was administered intra-articularly once a day for 14 d. The knee joints were assessed by roentgenography, histology, and gelatinase activity. HPE inhibited PG degradation in articular cartilage explants. HPE significantly reduced deformity of knee joints and suppressed the histological change in MIA-induced OA. HPE inhibited MMP-2 activity in MG-63 cells. MMP-2 and -9 activities were also reduced in the cartilages of HPE-treated knee joints. Our results indicate that HPE has therapeutic effects on OA by protecting cartilage.

Efficient Hybrid Solar Cells Based on Meso-Superstructured Organometal Halide Perovskites

Abstract: The energy costs associated with separating tightly bound excitons (photoinduced electron-hole pairs) and extracting free charges from highly disordered low-mobility networks represent fundamental losses for many low-cost photovoltaic technologies. We report a low-cost, solution-processable solar cell, based on a highly crystalline perovskite absorber with intense visible to near-infrared absorptivity, that has a power conversion efficiency of 10.9% in a single-junction device under simulated full sunlight. This "meso-superstructured solar cell" exhibits exceptionally few fundamental energy losses; it can generate open-circuit photovoltages of more than 1.1 volts, despite the relatively narrow absorber band gap of 1.55 electron volts. The functionality arises from the use of mesoporous alumina as an inert scaffold that structures the absorber and forces electrons to reside in and be transported through the perovskite.

Sequential deposition as a route to high-performance perovskite-sensitized solar cells

Abstract: Following pioneering work, solution-processable organic-inorganic hybrid perovskites-such as CH3NH3PbX3 (X = Cl, Br, I)-have attracted attention as light-harvesting materials for mesoscopic solar cells. So far, the perovskite pigment has been deposited in a single step onto mesoporous metal oxide films using a mixture of PbX2 and CH3NH3X in a common solvent. However, the uncontrolled precipitation of the perovskite produces large morphological variations, resulting in a wide spread of photovoltaic performance in the resulting devices, which hampers the prospects for practical applications. Here we describe a sequential deposition method for the formation of the perovskite pigment within the porous metal oxide film. PbI2 is first introduced from solution into a nanoporous titanium dioxide film and subsequently transformed into the perovskite by exposing it to a solution of CH3NH3I. We find that the conversion occurs within the nanoporous host as soon as the two components come into contact, permitting much better control over the perovskite morphology than is possible with the previously employed route. Using this technique for the fabrication of solid-state mesoscopic solar cells greatly increases the reproducibility of their performance and allows us to achieve a power conversion efficiency of approximately 15 per cent (measured under standard AM1.5G test conditions on solar zenith angle, solar light intensity and cell temperature). This two-step method should provide new opportunities for the fabrication of solution-processed photovoltaic cells with unprecedented power conversion efficiencies and high stability equal to or even greater than those of today's best thin-film photovoltaic devices.

Lead Iodide Perovskite Sensitized All-Solid-State Submicron Thin Film Mesoscopic Solar Cell with Efficiency Exceeding 9%

Abstract: We report on solid-state mesoscopic heterojunction solar cells employing nanoparticles (NPs) of methyl ammonium lead iodide (CH3NH3)PbI3 as light harvesters. The perovskite NPs were produced by reaction of methylammonium iodide with PbI2 and deposited onto a submicron-thick mesoscopic TiO2 film, whose pores were infiltrated with the hole-conductor spiro-MeOTAD. Illumination with standard AM-1.5 sunlight generated large photocurrents (JSC) exceeding 17 mA/cm2, an open circuit photovoltage (VOC) of 0.888 V and a fill factor (FF) of 0.62 yielding a power conversion efficiency (PCE) of 9.7%, the highest reported to date for such cells. Femto second laser studies combined with photo-induced absorption measurements showed charge separation to proceed via hole injection from the excited (CH3NH3)PbI3 NPs into the spiro-MeOTAD followed by electron transfer to the mesoscopic TiO2 film. The use of a solid hole conductor dramatically improved the device stability compared to (CH3NH3)PbI3 -sensitized liquid junction cells.

Long-Range Balanced Electron- and Hole-Transport Lengths in Organic-Inorganic CH3NH3PbI3

Abstract: Low-temperature solution-processed photovoltaics suffer from low efficiencies because of poor exciton or electron-hole diffusion lengths (typically about 10 nanometers). Recent reports of highly efficient CH3NH3PbI3-based solar cells in a broad range of configurations raise a compelling case for understanding the fundamental photophysical mechanisms in these materials. By applying femtosecond transient optical spectroscopy to bilayers that interface this perovskite with either selective-electron or selective-hole extraction materials, we have uncovered concrete evidence of balanced long-range electron-hole diffusion lengths of at least 100 nanometers in solution-processed CH3NH3PbI3. The high photoconversion efficiencies of these systems stem from the comparable optical absorption length and charge-carrier diffusion lengths, transcending the traditional constraints of solution-processed semiconductors.

The emergence of perovskite solar cells

Abstract: Within the space of a few years, hybrid organic–inorganic perovskite solar cells have emerged as one of the most exciting material platforms in the photovoltaic sector. This review describes the rapid progress that has been made in this area.