Do Kyung Lee

Enhancing the ionic transport of PEO-based composite polymer electrolyte by addition of TiO2 nanofiller for quasi-solid state dye-sensitized solar cells

For the application to quasi-solid state dye-sensitized solar cells (QS-DSSCs), we have prepared composite polymer electrolytes with a poly(ethylene oxide) (PEO)-TiO2-LiI-I2 system. Effects of the concentration of TiO2 nanofiller on the electrochemical properties of the PEO-based composite polymer electrolytes have been investigated. The experimental results show that the presence of TiO2 in the PEO-based electrolyte changes the phase of the polymer. Also, the addition of TiO2 noticeably increases the ionic conductivity of the PEO-based electrolytes. At optimized TiO2 concentration of 15 wt%, the composite polymer electrolyte exhibited a maximum value of ionic conductivity, and leads to remarkable enhancement of the photovoltaic performance of the QS-DSSC. This indicates that the incorporation of TiO2 to the PEO-based electrolytes gives rise to the reduction of the crystallinity of the polymer and the enhancement of the mobility of the I−/I3− redox couple, resulting in the increases of the conductivity and the current density of QS-DSSC.

Synthesis and Characterization of Organic Photo-Sensitizers Containing Multi-Acceptors for the Application of Dye-Sensitized Solar Cells

Organic photo-sensitizers containing multi-acceptors in a chromophore have been synthesized and characterized for the application of dye-sensitized solar cell (DSSC). In this study, we have used intramolecular push-pull system containing triphenylamine as the electron donor with different number of cyanoacetic acid moieties as electron acceptor/anchoring groups in a chromophore. The experimental results have revealed that when the induced electron acceptor increases, the larger amounts of dyes are adsorbed on the TiO2 surface in DSSC, resulting in the increase of short circuit photocurrent density. Our results suggest that the organic dyes with multi-electron acceptors moieties are promising for getting higher solar-to-electricity conversion efficiencies in DSSC.

Improved Efficiency of Dye-Sensitized Solar Cell Using Graphene-Coated Al2O3-TiO2 Nanocomposite Photoanode

Dye-sensitized solar cells (DSSCs) were fabricated using graphene-coated Al2O3 (GCA)-TiO2 nanocomposite electrodes. The GCA-TiO2 pastes were prepared by simply blending the GCA particles with TiO2 particles without any complex treatments. The DSSC with 1 wt.% GCA-TiO2 exhibited much better overall energy conversion efficiency, when compared to the DSSCs with TiO2 alone and with carbon nanotube-TiO2. It can be attributed to efficient electron transport through the GCA-TiO2 to the transparent conducting oxide, resulting in significantly enhanced electron lifetime.

Enhancing the Surface Wettability of Poly(Ethylene Terephthalate) Film by Atmospheric Pressure Plasma Treatment with Ar and N2Gas Mixture

In this work, the specific influences of atmospheric pressure plasma (APP) treatment on the surface modifications of poly(ethylene terephthalate) (PET) polymeric film have been explored. The APP was generated using dielectric barrier discharge in the ambient of Ar and N2gas mixture. Experimental results of the surface properties are presented for the PET film before and after the APP treatment. The exposure of PET films to APP leads to the roughening surface. Also, the APP-induced modifications are associated with incorporation of polar oxygen and nitrogen containing groups on the PET surface. Due to the changes of chemical composition and topology on the surface by the APP treatment, the contact angle of distilled water on the surface becomes smaller, resulting in higher surface wettability.

Enhancement of light harvesting in dye-sensitized solar cells by using Först-type resonance energy transfer

The improvement of solar energy-to-electricity conversion efficiency has continued to be an important research area for various solar cell devices. The fluorescence material was adsorbed on the TiO2 photo-electrode with sensitizers in dye-sensitized solar cell (DSSC) to enhance the photon-to-current efficiency. The improved light harvesting efficiency which was achieved by the judicious choice/design of fluorescence material and sensitizing dyes enhances the photovoltaic performance of the DSSCs with the Först-type resonance energy transfer (FRET). The energy acceptor (N719) should absorb the fluorescence emitted from the energy acceptor on the photo-electrode surface which could enhance the light harvesting property of sensitizer in DSSC. We achieved the significant enhancement of short circuit current density (Jsc) in DSSC by the FRET system on the photo-electrode surface. The photovoltaic performance of DSSCs containing FRET system was observed with I-V curve and incident photon-to-current efficiency. The electrical property and electron life time of DSSC was measured by using the impedance measurement method.

Synthesis and Photovoltaic Properties of Organic Photosensitizers Based on Phenothiazine Chromophore for Application of Dye-Sensitized Solar Cells

We developed organic dye containing the multi-chromophororic system in a molecule by connecting two individual chromophores with alkyl chain directly forusein DSSCs. Each of chromophore contains phenothiazine moiety as an electron donor and various electron acceptor/anchor to identify the effects of the number of electron acceptor and the kind of electron acceptor on the performance of DSSCs. The molecular structure having multi-chromophoric system containing cyanoacrylic acid moieties provided about 10% higher Jsc value than their counter parts of single-chromophore type.

Effects of Solvents on ITO Cracks in Ultrasonic Cleaning of ITO-Coated Flexible Substrates for Polymer Solar Cells

We report an experimental optimization of the cleaning process in the fabrication of flexible polymer solar cells using an indium tin oxide (ITO) coated poly(ethylene naphthalate) (PEN) substrate. The effects of the solubility parameters of the cleaning solvents on the occurrence of ITO cracks have been systematically investigated. The experimental results showed that the ITO cracks caused during the ultrasonic cleaning process were mainly affected by differences between the solubility parameters of the solvent and that of the PEN substrate, not by direct interaction between the solvent and the ITO layer. Our results provide a simple method for reducing ITO cracks during wet cleaning processes by selecting solvents with solubility parameters which differ significantly from those of the flexible substrates.

Synthesis and Photovoltaic Performance of Long Wavelength Absorbing Organic Dyes for Dye-Sensitized Solar Cells

We prepared novel organic photo-sensitizers based on a carbazole framework containing various acceptors with thiophene bridge units in the chromophore for the application to dye-sensitized solar cell (DSSC). Furthermore, organic dyes without bridge in the chromophore also synthesized to investigate the correlation between conjugation lengths and photon-to-current efficiency (PCE). Compared to non-bridged dyes, the DSSCs device containing multi-anchoring dyes with thiophene bridge exhibited much higher PCEs, resulting from efficient electron extraction pathways, higher molar extinction coefficients, and better light absorption in longer wavelengths.

Characteristics of Silicon Oxynitride Barrier Films Grown on Poly(ethylene naphthalate) by Ion-Beam-Assisted Deposition

For the application of transparent barriers to water vapor permeation for plastic substrates, we have prepared silicon oxynitride thin films on a poly(ethylene naphthalate) substrate at room temperature by the ion-beam-assisted electron beam evaporation method and investigated their characteristics with respect to N2 flow rate in the ion source. The experimental results reveal that when N2 flow rate increases, the nitrogen concentration and Si–N bonding in SiOxNy films increase owing to the assisted N2 ion incorporations during the film deposition process. Also, with increasing N2 flow rate, the surface roughness and optical transmittance of the barrier film decrease, whereas refractive index and film density increase. It is confirmed that the water vapor transmission rate of our barrier films decreases with the incorporation of N2 ions into the films, being strongly dependent on surface roughness and film density.

Influence of Oxygen Flow Rate on the Properties of ITO Films Prepared by Low-Frequency (60 Hz) Magnetron Sputtering

In this study, indium tin oxide (ITO) films were deposited at 300°C on glass substrates by low-frequency (60 Hz) magnetron sputtering technique. The influence of oxygen flow rate on the structural, electrical and optical properties of ITO thin films was investigated. The oxygen flow rate was varied from 0 to 8 sccm. We obtained the most superior property of ITO films at oxygen flow rate of 0.5 sccm. The films are found to show preferential orientation both (222) and (400) planes in the XRD patterns. The resistivity of the films with the thickness of 140 nm is 2.1 × 10−4 ohm · cm with 88% optical average transmittance in visible range (500–800 nm). Therefore, we conclude that transparent conducting ITO films prepared by low-frequency magnetron sputtering can be applied for various flat panel displays.