Yongseok Jun

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.

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.

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.

Effective Methods for the High Efficiency Dye-Sensitized Solar Cells Based on the Metal Substrates

A nano porous dye-sensitized solar cell (DSSC) has been widely studied since its origin by O’Regan and Gratzel.[1] By virtue of many sincere attempts, a conversion efficiency of more than 11%[2] and long-term stability[3] has been achieved using a DSSC with F-doped SnO2 layered glass (FTO-glass). However, relatively low conversion efficiency of the DSSC, compared with the crystalline Si (24.7%) or thin film CIGS (19.9%), restricts its further applications so far.[4] In order to improve the conversion efficiency of the DSSC, continuous attempts have been made in the past decades. Researchers have concentrated their attention on the working or counter electrode materials, synthesizing dye, additives of the electrolytes, nano-structures for enhancing light scattering and so on.[5-9] However, there have been few reports on the interface between nano-crystalline electrode material and current collecting substrates, in particular on the DSSC with thin and light-weight metal substrates. A DSSC with thin and lightweight substrate could extend its application. However, widely used conductive-layer-coated plastic films such as indium doped tin oxide (ITO) coated polyethylene terephthalate (PET) or polyethylene naphthalate (PEN) film degrade at the TiO2 sintering temperature of approximately 500 oC. Furthermore, thermal treatment of TiO2 particles below plastic degeneration temperature causes poor necking of TiO2 particles, resulting in a low conversion efficiency.[10] Several methods have been tried in order to answer to this problem, such as hydrothermal crystallization,[11] electrophoretic deposition under high DC fields,[12] and low temperature sintering.[13] However, these methods did not show the fundamental solution for the low necking problem. For better attempts, instead of plastic film, previous study has proposed thin metal foil as a substrates.[14-16] A thin metal foil can be a excellent alternative to conductive-layer-coated plastic films, because temperature limitation due to substrate could be eliminated. Focusing on the characteristics of the interface between nano-sized TiO2 and metal substrates, this chapter describes several effective methods for the high efficiency DSSCs