Publications (22)109.94 Total impact
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Article: Suppressed recombination in quantum dot-sensitized solar cells with blocking layers on FTO substrates.
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ABSTRACT: The compact and thin TiO2 blocking layers (c-TiO2) were formed on F-doped SnO2 (FTO) substrate in quantum dots-sensitized solar cells (QSSCs) by chemical deposition. The c-TiO2 layers induced indirect contact between electrolyte and FTO electrode, which reduced leakage in QSSCs. The QSSCs showed power conversion efficiency (Eff) of 3.85% in the presence of c-TiO2 layers which leads to 21% improved compared to that without c-TiO2 layers (Eff = 3.18%). The presence of the c-TiO2 layers in QSSCs also improved the stability under illumination.Journal of Nanoscience and Nanotechnology 02/2012; 12(2):1492-6. · 1.56 Impact Factor -
Article: Voltage-enhancement mechanisms of an organic dye in high open-circuit voltage solid-state dye-sensitized solar cells.
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ABSTRACT: Sensitization of solid-state dye-sensitized solar cells (SSDSSCs) with a new, organic donor-π-acceptor dye with a large molar absorption coefficient led to an open-circuit voltage of over 1 V at AM1.5 solar irradiance (100 mW/cm(2)). Recombination of electrons in the TiO(2) film with the oxidized species in the hole-transfer material (HTM) was significantly slower with the organic dye than with a standard ruthenium complex dye. Density functional theory indicated that steric shielding of the electrons in the TiO(2) by the organic dye was important in reducing recombination. Preventing the loss of photoelectrons resulted in a significant voltage gain. There was no evidence that the organic dye contributed to the high voltage by shifting the band edges to more negative electrode potentials. Compared with an iodide-based liquid electrolyte, however, the more positive redox potential of the solid-state HTM used in the SSDSSCs favored higher voltages.ACS Nano 09/2011; 5(10):8267-74. · 10.77 Impact Factor -
Article: Fabrication of mesoporous titania membrane of dual-pore system and its photocatalytic activity and dye-sensitized solar cell performance.
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ABSTRACT: We report the fabrication of a novel titania membrane of the dual-pore system that is strategically designed and prepared by a two-step replication process and sol-gel reaction. The primary nanoporous channel structure is fabricated by the cage-like PMMA template (CPT) obtained from the nanoporous alumina membrane and the secondary mesoporous structure is formed by the sol-gel reaction of the lyotropic precursor solution within the CPT. Furthermore the mesoporous titania membrane (MTM) frame consists of the titania nanoparticles of 10-12 nm in diameter. Morphology and structural properties of the MTM are investigated by field emission scanning electron microscopy, high resolution transmission electron microscopy, x-ray diffraction and Brunauer-Emmett-Teller surface area. The photocatalytic activity and the solar energy properties of the MTM are characterized by UV-vis spectrophotometer, spectrofluorometer and photoinduced I-V measurement. The photocatalytic test indicates that the MTM has higher efficiency than the commercial P25 with a good recyclability due to its large-scale membrane style and the preliminary result on the solar cell application shows a solar energy conversion efficiency of 3.35% for the dye-sensitized solar cell utilizing the MTM.Nanotechnology 07/2011; 22(27):275309. · 3.98 Impact Factor -
Article: Organic-inorganic hybrid tandem multijunction photovoltaics with extended spectral response
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ABSTRACT: We demonstrate series-connected hybrid tandem multijunction photovoltaics by combining hydrogenated amorphous silicon (a-Si:H) and polymer-based organic photovoltaics (OPVs). To utilize the wide solar spectrum with cost-effective processes, we employed a solution-processed low band gap OPV subcell onto the a-Si:H subcell. The interfacial contact between the subcells strongly affects the photovoltaic performance of the tandem cells. By using MoO3 as an efficient hole transporting intermediate layer instead of the conventional conducting polymer, we obtained power conversion efficiency of 1.84% and open-circuit voltage (VOC) of 1.50 V which corresponds closely to the sum of VOCs of the subcells.Applied Physics Letters 05/2011; 98(18):183503-183503-3. · 3.84 Impact Factor -
Article: Synthetic Strategy of Low-Bandgap Organic Sensitizers and Their Photoelectron Injection Characteristics
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ABSTRACT: Low-bandgap organic sensitizers are designed and synthesized for high photocurrent generation in dye-sensitized solar cell. Introduction of the -conjugated benzothiadiazole (BTD) unit in K1, designated as K2, decreases the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap energy from 2.63 to 2.10 eV, whereas the photovoltaic performance is not improved although the absorption threshold in incident photon-to-current conversion efficiency spectrum is extended from 650 nm to approximately 800 nm. Low photovoltaic performance is overcome by introduction of a phenylenevinylene moiety next to the BTD unit in K2, designated as K3 that shows similar HOMO-LUMO gap energy and absorbance to those of K2. As a result, a K3-sensitized 5 m-thick TiO solar cell demonstrates photocurrent density of 12.24 mA/cm, voltage of 0.549 V, and conversion efficiency of 3.8%, which is better than the conversion efficiency of 2.49% for K2 with photocurrent density of 8.13 mA/cm and voltage of 0.470 V. According to nanosecond transient absorption spectroscopic study, photoexcited electron injection efficiency of K3 is found to be three times higher than that of K2, which is attributed to the higher photocurrent of K3.IEEE Journal of Selected Topics in Quantum Electronics 01/2011; · 3.78 Impact Factor -
Article: Expanding the spectral response of a dye-sensitized solar cell by applying a selective positioning method.
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ABSTRACT: We have developed a facile method to position different dyes (N719 and N749) sequentially in a mesoporous TiO(2) layer through selective desorption and adsorption processes. From the selective removal of the only upper part of the first adsorbed dye, double-layered dye-sensitized solar cells have been successfully achieved without any damage to the dye. From the incident photon-to-current conversion efficiency (IPCE) measurement, the multi-layered dye-sensitized solar cell (MDSSC) was found to exhibit an expanded spectral response for the solar spectrum while maintaining the maximum IPCE value of each single-layered cell. The highest photocurrent density, 19.3 mA cm( - 2), was obtained from the MDSSC utilizing an N719/N749 bi-layered mesoporous TiO(2) film. The power conversion efficiency of 9.8% was achieved from the MDSSC, which is higher than that of single N719-or N749-based cells and cocktail-dyed (a mixture of N719 and N749) cells.Nanotechnology 01/2011; 22(4):045201. · 3.98 Impact Factor -
Article: Tandem Photovoltaic Cells with Amorphous Silicon Cells and Organic Photovoltaic Cells
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ABSTRACT: We demonstrate series-connected tandem photovoltaic cells consisting of hydrogenated amorphous silicon (a-Si:H) solar cells and polymer-based organic photovoltaic (OPV) cells. One of the limiting factors of a-Si:H solar cells is their narrow absorption spectrum as compared with that of crystalline silicon solar cells. In order to overcome this limitation, we fabricated a hybrid tandem solar cell by employing a solution-processed OPV subcell based on a low bandgap semiconducting polymer onto the a-Si:H subcell. It was found that the interfacial property of the hole transporting intermediate layer between the subcells strongly affects the photovoltaic property of the tandem cells. By using MoO3 as an efficient hole transporting intermediate layer instead of the conventional conducting polymer, we obtained the power conversion efficiency of 1.84% and the open-circuit voltage (VOC) of 1.50 V which corresponds closely to the sum of the VOCs of the subcells.MRS Proceedings. 12/2010; 1288. -
Article: Method to protect charge recombination in the back-contact dye-sensitized solar cell.
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ABSTRACT: We prepared a back-contact dye-sensitized solar cell and investigated effect of the sputter deposited thin TiO₂ film on the back-contact ITO electrode on photovoltaic property. The nanocrystalline TiO₂ layer with thickness of about 11 μm formed on a plain glass substrate in the back-contact structure showed higher optical transmittance than that formed on an ITO-coated glass substrate, which led to an improved photocurrent density by about 6.3%. However, photovoltage was found to decrease from 817 mV to 773 mV. The photovoltage recovered after deposition of a 35 nm-thick thin TiO₂ film on the surface of the back-contact ITO electrode. Little difference in time constant for electron transport was found for the back-contact ITO electrodes with and without the sputter deposited thin TiO₂ film. Whereas, time constant for charge recombination increased after introduction of the thin TiO₂ film, indicating that such a thin TiO₂ film protected back electron transfer, associated with the recovery of photovoltage. As the result of the improved photocurrent density without deterioration of photovoltage, the back-contact dye-sensitized solar cell exhibited 13.6% higher efficiency than the ITO-coated glass substrate-based dye-sensitized solar cell.Optics Express 09/2010; 18 Suppl 3:A395-402. · 3.59 Impact Factor -
Article: High performance organic photosensitizers for dye-sensitized solar cells.
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ABSTRACT: We report highly efficient organic photosensitizers containing pi-conjugated alkoxy-substituted oligophenylenevinylene linkers with electron donor-acceptor units for dye-sensitized solar cells. TA-DM-CA showed an overall solar-to-energy conversion efficiency of 9.67% at AM 1.5 illumination (100 mW cm(-2)).Chemical Communications 02/2010; 46(8):1335-7. · 6.17 Impact Factor -
Article: Selective positioning of organic dyes in a mesoporous inorganic oxide film.
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ABSTRACT: Although sequential adsorption of dyes in a single TiO(2) electrode is ideal to extend the range of light absorption in dye-sensitized solar cells, high-temperature processing has so far limited its application. We report a method for selective positioning of organic dye molecules with different absorption ranges in a mesoporous TiO(2) film by mimicking the concept of the stationary phase and the mobile phase in column chromatography, where polystyrene-filled mesoporous TiO(2) film is explored for use as a stationary phase and a Brønsted-base-containing polymer solution is developed for use as a mobile phase for selective desorption of the adsorbed dye. By controlling the desorption and adsorption depth, yellow, red and green dyes were vertically aligned within a TiO(2) film, which is confirmed by an electron probe micro-analyser. The external quantum efficiency (EQE) spectrum from a solar cell with three selectively positioned dyes reveals the EQE characteristics of each single-dye cell.Nature Material 07/2009; 8(8):665-71. · 32.84 Impact Factor -
Article: Formation of Highly Efficient Dye‐Sensitized Solar Cells by Hierarchical Pore Generation with Nanoporous TiO2 Spheres
Advanced Materials 05/2009; 21(36):3668 - 3673. · 13.88 Impact Factor -
Article: Formation of efficient dye-sensitized solar cells by introducing an interfacial layer of long-range ordered mesoporous TiO2 thin film.
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ABSTRACT: Long-range ordered cubic mesoporous TiO 2 films with 300 nm thickness were fabricated on fluorine-doped tin oxide (FTO) substrate by evaporation-induced self-assembly (EISA) process using F127 as a structure-directing agent. The prepared mesoporous TiO 2 film (Meso-TiO 2) was applied as an interfacial layer between the nanocrystalline TiO 2 film (NC-TiO 2) and the FTO electrode in the dye-sensitized solar cell (DSSC). The introduction of Meso-TiO 2 increased J sc from 12.3 to 14.5 mA/cm (2), and V oc by 55 mV, whereas there was no appreciable change in the fill factor (FF). As a result, the photovoltaic conversion efficiency ( eta) was improved by 30.0% from 5.77% to 7.48%. Notably, introduction of Meso-TiO 2 increased the transmittance of visible light through the FTO glass by 23% as a result of its excellent antireflective role. Thus the increased transmittance was a key factor in enhancing the photovoltaic conversion efficiency. In addition, the presence of interfacial Meso-TiO 2 provided excellent adhesion between the FTO and main TiO 2 layer, and suppressed the back-transport reaction by blocking direct contact between the electrolyte and FTO electrode.Langmuir 11/2008; 24(22):13225-30. · 4.19 Impact Factor -
Article: Transparent solar cells based on dye‐sensitized nanocrystalline semiconductors
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ABSTRACT: Low-cost dye-sensitized solar cells have attracted much attention because of their unique characteristics of transparency and various colors. A dye-sensitized solar cell is composed of a dye-coated nanocrystalline wide-bandgap semiconductor, redox electrolyte and platinum counter-electrode. Transparency and various colors are attributed to a 10–20 μm thick semiconductor film with particle size of about 10–20 nm and a difference in HOMO–LUMO energies of the dye molecules, respectively. A biomimetic working principle enables effective electron injection and regeneration. Recent research on dye-sensitized solar cells has been focused on the improvement of solar-to-electricity conversion efficiency as well as long-term stability. In this report, the recent advances of transparent solar cells based on dye-sensitized semiconductors are reviewed. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)Physica Status Solidi (A) Applications and Materials 05/2008; 205(8):1895 - 1904. · 1.46 Impact Factor -
Article: Fabrication of heterosensitizer-junction dye-sensitized solar cells
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ABSTRACT: We report here a dye-sensitized solar cell structure having two different dyes with complementary absorption properties, which is different from the dye-cocktail method. The developed method allows two different dyes to be adsorbed on the sintered Ti O <sub>2</sub> layers without thermal decomposition, which the conventional procedure of dye-sensitized solar cell has been unable to do. The contribution of different dyes to photocurrent generation has been confirmed by incident-photon-to-current conversion efficiency (IPCE) and photocurrent transient spectroscopy. The heterosensitizer-junction type demonstrates higher IPCE than the single-sensitizer structure, thanks to complementary absorption characteristics.Applied Physics Letters 05/2008; · 3.84 Impact Factor -
Article: A highly efficient organic sensitizer for dye-sensitized solar cells.
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ABSTRACT: We have synthesized a highly efficient organic dye for a dye-sensitized solar cell; the overall solar-to-energy conversion efficiency was 9.1% at AM 1.5 illumination (100 mW cm(-2)): short-circuit current density (J(sc)) = 18.1 mA cm(-2), open circuit photovoltage (V(oc)) = 743 mV and fill factor (ff) = 0.675.Chemical Communications 01/2008; · 6.17 Impact Factor -
Article: Role of Au nanoparticles in efficiency enhancement and green band emission quenching of blue polymer light emitting diodes.
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ABSTRACT: We studied photoluminescence (PL) and electroluminescence (EL) properties of polymer light emitting diodes (PLEDs) constructed with polyconjugated polymers blends containing Au nanoparticles (DA-Au NPs; 5.3 nm +/- 1.1 nm in diameter) capped by dodecylamine. For the blue light emitting polyfluorene polymers, selective quenching of excimer peaks or so-called green bands was observed in PL as well as in EL when they were mixed with small amounts (1-4 wt%) of DA-Au NP. The influence of DA-Au NPs on the light-emitting characteristics of the PLEDs strongly depended on the nature of the matrix polymer, which was particularly conspicuous for the polymers whose emission wavelength matches or overlaps with the surface plasmon resonance wavelength region of Au nanoparticles. Especially, the purity of the blue color emitted by the poly [2,7-(9,9-di-n-dioctylfluorene) (PF) was greatly improved by Au NPs that suppressed the 'green band.' All the PLEDs doped with DA-Au NPs showed enhanced maximum external quantum efficiency and emitted light intensity when compared to undoped counterparts.Journal of Nanoscience and Nanotechnology 12/2005; 5(11):1898-903. · 1.56 Impact Factor -
Article: Synthesis and Luminescent Properties of Fluorene Copolymers Bearing DCM Pendants
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ABSTRACT: A series of copolymers, poly[(9,9-dioctylfluorene-2,7-diyl)-co-(4-dicyanomethylene-2-methyl-6-[4-(diphenylamino)styryl]-4H-pyran-4‘,4‘ ‘-diyl)], were synthesized by polymerizing 2,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9,9-dioctylfluorene with mixtures of 2,7-dibromo-9,9-dioctylfluorene and 4-dicyanomethylene-2-methyl-6-[bis(4‘-bromophenyl)amino]styryl]-4H-pyran (a DCM derivative) by the palladium-catalyzed Suzuki coupling reaction. The copolymers were characterized by molecular weight determination, elemental analysis, 1H NMR, FT-IR spectroscopy, DSC, TGA, UV−vis spectroscopy, and photoluminescence (PL) and electroluminescence (EL) spectroscopy. The copolymers showed two absorption peaks at 380 and 485 nm, and the long-wavelength absorption increased with increasing the fraction of the DCM comonomer. The PL spectra of copolymers in chloroform solution displayed emission from both the main chain (420 nm) and DCM units (620 nm). In the solid state, however, PL spectra of copolymers showed only the long wavelength red emission at 620 nm with no trace of emission from the main chain, which implies a facile exciton migration or energy transfer to the lower energy sites from the fluorene part to the DCM part. This results in emission of only the red light originating from the latter segments. A study on time-resolved PL rise and decay of the polymers clearly supports the energy transfer mechanism. Light-emitting diode (LED) devices were fabricated to have the configuration of ITO (indium−tin oxide)/PEDOT/polymer/Li:Al alloy. EL spectra of the devices showed only red emissions as observed in the PL spectra of the polymers' thin films. EL efficiency decreased with increasing DCM contents. When a tris(8-hydroxyquinolinato)aluminum (Alq3) layer was inserted between the emitting polymer layer and the cathode to make the ITO/PEDOT/polymer/Alq3/Li:Al alloy configuration, the device efficiencies became much higher (10-2%) than those (5 × 10-5−5 × 10-3%) of single-layer devices.06/2005; -
Article: Optical absorption and photoluminescence properties of the PPV nanotubes and nanowires
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ABSTRACT: We measured optical absorption and time resolved photoluminescence decay properties of the PPV nanotubes and nanowires which were prepared by CVD polymerization using templates. When compared with bulk PPV films, their nano objects showed different optical properties, long photoluminescence decay time and higher photoluminescence efficiencies.Macromolecular Symposia 09/2003; 201(1):119 - 126. -
Article: Synthesis and Luminescence Properties of Poly[2-(9,9-dihexylfluorene-2-yl)-1,4-phenylenevinylene] and Its Copolymers Containing 2-(2-Ethylhexyloxy)-5-methoxy-1,4-phenylenevinylene Units
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ABSTRACT: A PPV derivative bearing the dihexylfluorenyl pendants, poly[2-(9,9-dihexylfluorene-2-yl)-1,4-phenylenevinylene] (DHF−PPV) and its copolymers containing the dialkoxy-substituted phenylenevinylene units, i.e., poly[(2-(9,9-dihexylfluorene-2-yl)-1,4-phenylenevinylene)-co-(2-(2-ethylhexyloxy)-5-methoxy-1,4-phenylenevinylene)s], were prepared, and luminescence properties of the light-emitting diodes (LEDs) fabricated with them were studied. The copolymers 92.5 DHF/7.5 MEH−PPV and 50.5 DHF/49.5 MEH−PPV contained 7.5 and 49.5 mol % of the dialkoxy comonomer units, respectively. The structure of LED devices was ITO/PEDOT (25 nm)/polymer (80 nm)/Ca (50 nm)/Al (50 nm). The wavelengths of maximum emitted light of the devices were 519 nm (green), 560 nm (yellow), and 585 nm (orange-red) for DHF−PPV and the two copolymers. Turn-on electric fields decreased in the order of DHF−PPV (0.54 MV/cm) > 92.5 DHF/7.5 MEH−PPV (0.43 MV/cm) > 50.5 DHF/49.5 MEH−PPV (0.29 MV/cm). Luminance efficiencies of the three devices were 2.3, 1.0, and 0.9 cd/A for 92.5 DHF/7.5 MEH−PPV, 50.5 DHF/49.5 MEH−PPV, and DHF−PPV, respectively. The maximum luminance for the device of DHF−PPV was 1.6 × 104 cd/m2, and the value increased to 2.7 × 104 cd/m2 for 97.5 DHF/7.5 MEH−PPV. The maximum luminance of the other copolymer was about 1.9 × 104 cd/m2. The study of time-resolved PL of the present polymers strongly suggests that a correlation exists between their PL decay behavior and EL efficiency. The mobilities of the charge carriers, i.e., hole and electron, are better balanced (υh/υe 10) in DHF−PPV than in MEH−PPV (υh/υe 102).03/2002; -
Article: ITO/ATO/TiO2 triple-layered transparent conducting substrates for dye-sensitized solar cells
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ABSTRACT: A novel transparent conductive oxide film based on the triple-layered indium tin oxide (ITO)/antimony-doped tin oxide (ATO)/titanium oxide (TiO2) has been developed for dye-sensitized solar cells by using radio frequency magnetron sputtering technique. Effects of the absence and presence of TiO2 layer and the ITO layer thickness were investigated. Deposition of ATO layer was found to stabilize the thermal instability of ITO. Little change in sheet resistance and optical transmittance was observed by introduction of insulating thin TiO2 layer on top of the ATO layer, whereas photovoltaic performance was significantly influenced. The conversion efficiency was improved from 4.57% without TiO2 layer to 6.29% with TiO2 layer. The enhanced photovoltaic performance with addition of TiO2 layer was attributed mainly to the improved adhesion and partially to the reduced electron loss at the ITO/ATO conductive layer. Increase in the ITO layer thickness resulted in a slight decrease in photocurrent due to the reduced optical transmittance. When compared with the conventional fluorine-doped tin oxide (FTO), the ITO/ATO/TiO2 conductive material exhibited similar photocurrent density but higher photovoltage and fill factor, resulting in better conversion efficiency.Solar Energy Materials and Solar Cells 92(8):873-877. · 4.54 Impact Factor
Top co-authors
Top Journals
Institutions
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2008–2011
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Korea Institute of Science and Technology
Seoul, Seoul, South Korea
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2008–2010
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Inha University
- Department of Polymer Science and Engineering
Seoul, Seoul, South Korea
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2003–2005
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Korea University
Seoul, Seoul, South Korea
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