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The suitability of stainless steel for dye solar cell substrate was investigated with respect to performance and stability using photovoltaic characterization, electrochemical impedance spectroscopy (EIS), open circuit voltage decay (OCVD), and substrate polarization measurements. Stainless steel was employed both as photoelectrode and as counter electrode substrate gaining initial cell efficiencies of 4.7% and 3.5%, respectively. The leakage current from the stainless steel substrate was found to be very low. The effect of the stainless steel substrate on the performance of the other cell components was also examined. The traditional data analysis based on external cell voltage was shown to be inadequate and even misleading. Here, the voltage over a single cell component was determined computationally on the basis of EIS measurements as a function of cell current; through this approach, we found that the stainless steel counter electrode did not have any impact on the photoelectrode whereas the stainless steel photoelectrode substrate decreased the effective electron lifetime and the recombination resistance of the dyed TiO 2 film.

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Atomic layer deposited TiO 2 recombination blocking layers were prepared on ITO-PET photoelectrode substrates for dye solar cells and examined using several electrochemical methods. The blocking layers increased the open circuit voltage at low light intensities. At high light intensities decrease of the fill factor due to additional resistance of current transport through the layer was more significant than the positive effect by the reduced recombination. The decrease in the fill factor was reduced by thermal treatment that made the blocking layer more conductive due to a structural change from an amorphous to a crystalline form. Therefore, thinner blocking layers of this type are required for plastic cells prepared at low temperature than for conventional glass dye solar cells made with temperature processing.

In this study the stability of dye solar cells with different kinds of metals as the photoelectrode substrate is studied. Stainless steels, Inconel and titanium substrates were tested in order to find stable substrate options. Photovoltaic characterization, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and substrate polarization measurements were used in the characterization.

SUMMARYThis review presents an overview of the current state of research on nanostructured titanium dioxide dye solar cells (DSCs) on alternative substrates to glass. Replacing the traditionally used heavy, rigid, and expensive glass substrate with materials such as plastic foils or metal sheets is crucial to enable large volume cost-efficient roll-to-roll type industrial scale manufacturing of the cells and to make this solar cell technology properly competitive with silicon and thin film photovoltaic devices. One of the biggest problems with plastic substrates is their low-temperature tolerance, which makes sintering of the photoelectrode films impossible, whereas with metals, their corrosion resistance against the iodine-containing electrolyte typically used in DSCs limits the amount of metal materials suitable for substrates. However, significant progress has been made in developing new materials, electrode film deposition and post-treatment methods suitable for low-temperature processing. Also, metals that do not corrode in the presence of iodine electrolyte have been found and successfully employed as DSC substrates. The highest power conversion efficiencies obtained with plastic and metal substrates are already 7-9%, which is not far from the best glass cell efficiencies, 10-11%, and comparable also to, for example, amorphous silicon solar cell efficiencies. One of the most important of the remaining research challenges of DSCs on flexible substrates is to ensure that the long-term stability of the cells is realistic to consumer applications, for example, with providing efficient enough encapsulation to prevent water and other impurities penetration into the cells. Degradation mechanisms specific to metal-based cells are another issue that needs deeper understanding still. More exotic approaches such as depositing the DSC structure on optical fiber or employing carbon nanomaterials to increase the cell efficiency are also discussed in this paper.

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