Man Gu Kang

Fabrication of an Efficient Dye-Sensitized Solar Cell with Stainless Steel Substrate

Highly efficient dye-sensitized solar cells (∼8.6%) using a flexible stainless steel substrate for preparation of a mesoporous TiO 2 film electrode were fabricated by controlling the dark current density. Optimal photovoltaic properties were obtained with a cell where the TiO 2 film was coated on a Ti-isopropoxide-treated stainless steel-based substrate. The quality of the underlayer was characterized and found to be related with the photovoltaic properties.

Dye-Sensitized TiO2 Solar Cells Using Polymer Gel Electrolytes Based on PVdF-HFP

The open-circuit voltage increases substantially and stability of dye-sensitized TiO 2 solar cells is improved when polymer gel containing poly(vinylidenefluoride-co-hexafluoropropylene) (PVdF-HFP) in N-methyl-2-pyrrolidone replaces commonly used solvents such as acetonitrile (ACN) and 3-methoxypropionitrile (MPN). The energy conversion efficiency of the cell with 6 wt % PVdF-HFP is comparable to that obtainable in ACN and in MPN. The promising effect of PVdF-HFP as a gelator is attributed to its interaction with Li + ions.

Redox supercapacitor using polyaniline doped with Li salt as electrode

Abstract We prepared polyaniline powder doped with LiPF 6 and utilized it as an electrode material in a polymer redox supercapacitor. The electrode sheet was fabricated by coating the slurry directly on a charge collector. We also compared the performance of porous polyolefin separator as supplied and the polymer electrolyte as prepared. The redox supercapacitor using the polyolefin separator exhibits ∼100 F/g specific capacitance at the initial discharge and retains ∼70 F/g after 5000 cycles, while the initial specific capacitance using the polymer electrolyte is ∼80 F/g and retains ∼60 F/g after 5000 cycles.

Effect of increased surface area of stainless steel substrates on the efficiency of dye-sensitized solar cells

In order to increase the electrical contact area between TiO2 particles and stainless steel (StSt) substrates of the dye-sensitized solar cells (DSSCs), StSt foil was roughened electrochemically using sulfuric acid with some additives. Compared with the DSSC with nontreated StSt substrate, DSSC with this roughened StSt substrate showed a 33% increase in light-to-electricity conversion efficiency with negligible effect on open circuit voltage (Voc) and fill factor. Electrochemical impedance spectroscopy clearly confirmed that the increased performance was due to a decreased electrical resistance at the TiO2/StSt interface.

Enhanced photo-conversion efficiency of CdSe–ZnS core–shell quantum dots with Au nanoparticles on TiO2 electrodes

This study demonstrates that configurations that include gold nanoparticles (Au NPs) as the primary layer attached to a TiO2 electrode with quantum dots (QDs) as the secondary layer have superior photoelectrochemical properties. We found that all Au–QD nanoparticle hybrid systems reveal enhanced photocurrent generation as compared to only a QD–nanoparticle interface. The enhanced Jsc is attributed to sensitization that results indirectly from quantum dots becoming attached to Au NPs by intramolecular charge transfers. As a result of the improved performance, the overall energy conversion efficiency was increased by 100% as compared to that of a reference cell without Au NPs at 100 mW cm−2. When (CdSe)ZnS is prepared from Au-coated TiO2, incident photon-to-current efficiency values approaching 20% can be achieved by (CdSe)ZnS devices. In the electrochemical impedance spectroscopy results, the intermediate frequency region of the Au–QD cells was more significantly reduced compared to that in bare QD cells due to the enhanced charge separation that occurs in the Au–QD structure. Mott–Schottky (C−2–ϕ) analysis shows that the lowest acceptor and donor densities having a positive effect on the efficiency could be found in (CdSe)ZnS–Au/TiO2 cells. Therefore, (CdSe)ZnS–Au/TiO2 has a very thin depletion layer that is restricted to the surface of Au/TiO2. Consequently, this system can be employed to enhance the effective efficiency in the design of the QD-sensitized solar cells.

The Characterization of Nanocrystalline Dye-Sensitized Solar Cells with Flexible Metal Substrates by Electrochemical Impedance Spectroscopy

Metal substrates are excellent alternatives to conducting plastic substrates in flexible solar cells because of the possible sintering process at high temperature. However, the investigation of cells with flexible metal substrates has only recently started with titanium, tungsten, and stainless steel. It was found that they formed semiconductor oxides after the sintering process. In this paper, we probed the properties of dye sensitized solar cells with the metal substrates prepared in three different ways-a bare metal sheet, indium tin oxide (ITO) sputter coating on a bare metal sheet, and ITO sputter coating after the addition of a SiO x layer on the metal sheet. The best cell efficiency was obtained from the cell with bare Ti because it formed a TiO 2 layer which was identical to the main working electrode. When an ITO layer was added, fill factors (FFs) increased for W and SUS 304 and FF decreased for Ti; the addition of a SiO x layer led to a short circuit current increase and FF decrease. Electrochemical impedance spectroscopy was taken and analyzed to characterize the resistance element in each circuit, and the corresponding effects were discussed. A new impedance element resulting from the SiO x insulating layer was classified from electrochemical impedance spectroscopic data.

Electrochemical properties of vanadium oxide thin film deposited by R.F. sputtering

Vanadium oxide (V2O5) thin films with various thicknesses have been prepared by using the radio frequency (R.F.) sputtering method from V2O5 (ceramic) or V (metal) target. The electrochemical properties of the films were characterized as a function of the thickness. The films with thickness of 500 nm fabricated from V2O5 ceramic target showed proper discharge capacity and cycle performance. However, the electrochemical property for the film with thickness of over 500 nm could not be observed due to the low deposition rate from V2O5 ceramic target and instability of interface between the surface and the film. The discharge capacity and cyclic performance of vanadium oxide films deposited from V metal target degraded with increasing thickness of the films. Considering the electrochemical properties of the films and the requirement of current density for the application field of thin film battery, appropriate thickness of vanadium oxide film for thin film battery was less than 1000 nm in our work. D 2002 Elsevier Science B.V. All rights reserved.

Iodide-functionalized graphene electrolyte for highly efficient dye-sensitized solar cells

1-Octyl-2,3-dimethylimidazolium iodide, ODI, was used as an electron acceptor to functionalize graphene to impart electrocatalytic activity for triiodide reduction in dye-sensitized solar cells (DSSCs). Raman and X-ray photoelectron spectroscopic measurements identified the graphene formation from graphene oxide with ODI. The resultant graphene positively charged via an intermolecular charge-transfer process with ODI showed remarkable electrocatalytic activity toward triiodide reduction. The inner work mechanism of solar cell devices was analyzed by intensity-modulated photovoltage spectroscopy, by intensity modulated photocurrent spectroscopy, and through an analysis of photovoltage transients. The results indicated that ODI-graphene electrolyte provides effective intermolecular charge transfer, thus making it feasible for use in the creation of high-performance DSSC devices.

Novel ionic iodide-siloxane hybrid electrolyte for dye-sensitized solar cells.

A novel ionic siloxane hybrid electrolyte was fabricated by thermal polymerization of iodide-oligosiloxane resin. The nanosized iodide-oligosiloxane was synthesized by a simple sol-gel condensation of 3-iodopropyltrimethoxysilane and diphenylsilanediol. It is found that the composition and concentration of the oligosiloxane used in the electrolyte affect the performance of the dye-sensitized solar cells (DSSCs). An optimized DSSC with the hybrid electrolyte using smaller molecular-sized oligosiloxane with a greater amount of iodide groups presented solar to electricity conversion efficiency of 5.2% at 1 sunlight (100 mW cm(-2)), which is comparable to that afforded by a liquid electrolyte.

Efficiency enhancement of semi-transparent sandwich type CH3NH3PbI3 perovskite solar cells with island morphology perovskite film by introduction of polystyrene passivation layer

Highly semi-transparent sandwich type CH3NH3PbI3 (MAPbI3) island perovskite solar cells with high efficiency were constructed by introduction of a polystyrene (PS) passivation interlayer. The PS insulator can prevent direct contact between the TiO2 electron conductor and the polytriarylamine hole conductor. The PS passivation interlayer could be selectively deposited on bare TiO2 by a consecutive spin-coating and spin-washing process. The average visible transmittance of semi-transparent sandwich type MAPbI3 island perovskite solar cells with and without PS passivation layer was ∼20.9% and ∼18.6%, respectively; its power conversion efficiency was 10.2% for forward scan condition and 10.6% for reverse scan condition (average = 6.17% ± 2.32% for 40 samples) and 5.9% for forward scan condition and 6.6% for reverse scan condition (average = 2.93% ± 1.57% for 40 samples); and its efficiency degradation for 30 days was ∼5% and ∼9%, respectively.