Kang-Jin Kim

High-Performance Quasi-Solid-State Dye-Sensitized Solar Cell Based on an Electrospun PVdF−HFP Membrane Electrolyte

An electrospun membrane was prepared from a 16 wt % solution of poly(vinylidenefluoride- co-hexafluoropropylene) (PVdF-HFP) in a mixture of acetone/ N, N-dimethylacetamide (7:3 wt %) at an applied voltage of 12 kV. It was then activated by immersing it in 0.6 M 1-hexyl-2,3-dimethylimidazolium iodide, 0.1 M LiI, 0.05 M I 2, and 0.5 M 4- tert-butylpyridine in ethylene carbonate/propylene carbonate (1:1 wt %) to obtain the corresponding membrane electrolyte with an ionic conductivity of 10 (-5) S cm (-1) at 25 degrees C. On the basis of this electrospun membrane electrolyte, quasi-solid-state dye-sensitized solar cells were fabricated, which showed an open-circuit voltage ( V oc) of 0.76 V, a fill factor of 0.62, and a short-circuit current density ( J sc) of 15.57 mA cm (-2) at an incident light intensity of 100 mW cm (-2). This yields a light-to-electricity conversion efficiency of 7.3%. Moreover, this cell possessed better long-term stability than that fabricated with conventional liquid electrolyte.

Surface treatment and characterization of PMMA, PHEMA, and PHPMA

Poly(methylmethacrylate) (PMMA), poly(2-hydroxyethyl methacrylate (PHEMA), and poly(2-hydroxypropyl methacrylate) (PHPMA) were modified to improve the wettability by two techniques: plasma and plasma source ion implantation. The modified surfaces were characterized to investigate the dependence of the modification and hydrophobic recovery on the polymer structure. The differences obtained under optimal experiment conditions among the polymers were interpreted in terms of their polymer structures including the glass transition temperature. The surface free energy, calculated from the contact angle measurements, revealed that its polar component was a dominant factor in improving the wettability. The PSII treatment created more functional groups on the surface and extensively modified the polymer layer than the plasma treatment.

Surface studies of plasma source ion implantation treated polystyrene

The plasma source ion implantation (PSII) was utilized to improve the wettability and the stability of surface layer formed in the modification of polymeric materials. Polystyrene was treated with different kinds of plasma ions to render the surface more hydrophilic or hydrophobic. Hydrophobic recovery of PSII-treated polystyrene was also observed as a function of aging time, aging temperature, and treatment parameters. Treatment parameters involve kinds of gases, pressure, plasma power, pulse frequency, pulse voltage, etc. To study the effect of inert gas on hydrophobic recovery, polystyrene samples were prepared by helium, argon, or gas-mixture treatment. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) has been used to interpret the PSII-treated polystyrene surface and its hydrophobic recovery, with the assistance of x-ray photoelectron spectroscopy and water contact angle measurements. TOF-SIMS spectra of 18O2 PSII-treated samples showed the presence of 18O-containing peaks from the modified ...

Surface modification of porous nanocrystalline TiO2 films for dye-sensitized solar cell application by various gas plasmas

Titanium dioxide (TiO2) film for dye-sensitized solar cells (DSSCs) has surface defects such as oxygen vacancies created during the annealing process. The authors used a plasma treatment technique to reduce defects on TiO2 surfaces. They investigated the influence of different gas plasma treatments of TiO2 film on the photoelectric performance of DSSC. Short-circuit photocurrent density (Jsc), open-circuit photovoltage (Voc), and the amount of adsorbed dye for DSSCs were measured. As a result, the solar-to-electricity conversion efficiencies of the O2- and N2-treated cells increased by 15%–20% compared to untreated cells. On the other hand, solar energy conversion efficiency of CF4-plasma treated cells decreased drastically. The increased amount of adsorbed dye on the TiO2 film was measured by time-of-flight secondary ion mass spectrometry. TiO2 surfaces modified by plasma treatment were characterized using analytical instruments such as x-ray photoelectron spectroscopy and near-edge x-ray absorption fine...

Titanium nitride thin film as a novel charge collector in TCO-less dye-sensitized solar cell

A titanium nitride (TiN)-based dye-sensitized solar cell is developed where TiN is used as a charge collector and TCO-less glass as a substrate. A nanocrystalline TiO2 film was deposited onto a TCO-less glass substrate using the radio frequency (r.f.) magnetron sputtering method and capped with a TiN film with a thickness of ∼66 to ∼167 nm, which was controlled by varying sputtering time. The crystal structure of TiN layers is analyzed using XRD, chemical bonding nature and composition (TiN0.95) were confirmed by XPS and RBS, respectively. Cross-sectional scanning electron microscopic images confirmed the columnar structure of TiN films. Electrical resistance is exponentially decayed and approaches 4.4 Ω as the TiN film thickness increases up to 167 nm. The photovoltaic property is significantly influenced by the TiN film thickness. The energy conversion efficiency increases from 3.3% to 6.8% with increasing the TiN film thickness from 66 nm to 86 nm, where an increase in fill factor from 0.33 to 0.64 is mainly responsible for the efficiency improvement. The highest efficiency of 7.4% is obtained with a 136 nm-thick TiN film and declines to 5.8% at 167 nm, resulting in a one order of magnitude retarded diffusion rate of I3−. A long-term stability test was performed for 1000 h and compared with a cell with pure Ti metal. The TiN-based cell maintains an efficiency of 84% after 1000 h, while the efficiency of the Ti-based cell is degraded by ∼34%, indicating that TiN is more stable than Ti in the TCO-less dye-sensitized solar cell.

High Performance Dye-Sensitized Solar Cells with Alkylpyridinium Iodide Salts in Electrolytes

Pyridinium iodide salts, which are competitive to the conventional imidazolium iodide salts, have been used for dye-sensitized solar cells as iodide sources and ionic conductivities. Pyridinium iodide series are easy to prepare and less expensive than the imidazolium series salts. In this research, quite comparable efficiencies were obtained from electrolytes with pyridinium iodide salts. For the experiments, pyridinium salts with a few different alkyl chains are applied. When a pyridinium head is modified to picolinium, which has a methyl group on the pyridinium head, a noticeable V(oc) drop has been observed. However, the length of the alkyl chains on the pyridinium head does not affect V(oc) effectively. The odd-numbered alkyl chains showed slightly lower V(oc) compared to that of the even-numbered alkyl chains. Finally, the performances of the cells with pyridinium salts are compared to those of the conventional cells with imidazolium salts.

Reduction in surface resistivity of polymers by plasma source ion implantation

The surface resistivity of several polymers such as poly(styrene/butadiene copolymer), modified poly(phenyleneoxide), poly(ethylene terephthalate), and polyimide was improved by the argon gas plasma source ion implantation (Ar-PSII) technique equipped with a mesh-type conducting grid. With the grid, the surface resistivities of the modified polymers decreased up to 11 orders of magnitudes at a high ion dose, and remained nearly at the same values after 3 months. The PSII treated polymer sample with the grid provided more uniformly modified surface and lower surface resistivity than that treated without the grid. The extent of the decrease in surface resistivity depended on the polymer structures and physical properties. However, the surface resistivity was independent of the sample thickness, the grid size, and the grid height. Surface analyses using scanning electron microscopy, time-of-flight secondary ion mass spectrometry, and Raman spectroscopy provided the useful information on modified surfaces.

Duplex plasma surface treatment process on mild steel and high alloyed tool steel

Duplex plasma surface treatment by calorizing and plasma nitriding was carried out on mild steel and high alloyed tool steel to improve their elevated temperature wear properties. Effects of calorizing on the plasma nitriding behavior of the steels and the characteristics of the duplex-treated specimens were analyzed using SEM, EDS, XRD, and a microhardness tester. Calorizing on mild steel created a FeAl compound layer of approximately 120 μm thickness, resulting in the improvement of the surface hardness by a factor of 2. Subsequent plasma nitriding increased the surface microhardness above 1200 Hv (0.1 kgf) and the nitriding depth was of the order of 80 μm. The high alloyed tool steels showed a decrease in microhardness in the Al-diffused layer upon calorizing. The subsequent plasma nitriding, however increased the hardness up to 1280 Hv and the nitriding depth of over 80 μm was obtained. The room temperature wear resistance of the duplex-treated steels was slightly better than that of the nitrided one, but there was considerable improvement in the high temperature wear resistance at 500°C in the duplex-treated steels when both the wear volume and the weight change due to oxidation were considered.

Effect of different compositions of ethylene carbonate and propylene carbonate containing iodide/triiodide redox electrolyte on the photovoltaic performance of DSSC

The effect of different compositions (in weight percent) of ethylene carbonate (EC) and propylene carbonate (PC) containing iodide/triiodide redox electrolyte on the photoelectrochemical performance of N719-sensitized nanocrystalline TiO2 solar cell was studied. The cells consisted of 0.6xa0M 1-hexyl-2,3-dimethylimidazolium iodide, 0.1xa0M LiI, 0.05xa0M I2 and 0.5xa0M 4-tert-butylpyridine in different compositions such as 1:1, 1:2, and 2:1xa0wt% of EC and PC. In 1:1xa0wt% of EC and PC containing redox electrolyte, short circuit photocurrent density (Jsc) increased and open circuit voltage (Voc) decreased. But in 1:2 and 2:1xa0wt% of EC and PC containing redox electrolytes, Voc increased and Jsc decreased but fill factor remained relatively constant. Dye-sensitized solar cells (DSSCs) prepared using these electrolytes give a short circuit photocurrent densities of 16.86, 12.71, and 12.09xa0mA/cm2; an open circuit voltages of 0.73, 0.78, and 0.79xa0V; fill factors of 0.63, 0.64, and 0.64; and an overall conversion efficiencies of 7.76, 6.34, and 6.13xa0% at an incident light of 100 mWcm−2 for 1:1, 2:1, and 1:2xa0wt% of EC/PC containing redox electrolytes, respectively. The incident photon-to-current conversion efficiency was higher in the case of 1:1xa0wt% of EC and PC containing redox electrolyte than 1:2 and 2:1xa0wt% of EC and PC containing redox electrolyte. It revealed that 1:1xa0wt% of EC and PC containing iodide/triiodide redox electrolyte is an effective electrolyte system for the fabrication of long-term stable DSSC.

Influence of nylon 6 in I3(-)/I(-) redox electrolyte on the photovoltaic performance and stability of dye-sensitized solar cells.

Nylon 6 fibers are used, for the first time, in dye-sensitized solar cells (DSSCs). The overall energy conversion efficiency obtained with 0.18 M nylon 6 reaches 6.2%, which is comparable to that (6.7%) obtained without adding nylon 6 on the day of cell fabrication. However, it is found that the long-term stability of the DSSCs with nylon 6 is superior to that of a reference electrolyte as a result of the complexation of nylon 6 with I(3)(-). Furthermore, nylon 6 is found to be a corrosion inhibitor for silver metal in the electrolyte containing I(3)(-).