Dye-sensitized solar cells on alternative substrates

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Aalto-yliopiston teknillinen korkeakoulu | Doctoral thesis (article-based)
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TKK dissertations, 214
Dye-sensitized solar cells (DSC) could become a potential alternative for the traditional silicon and thin film panels in the near future, due to the DSC's for the most part cheap materials and simple manufacturing methods. One of the challenges of this technology is, however, the heavy, expensive and inflexible glass substrate typically used in the cells. To address this problem, this thesis concentrates on transfer of the DSC technology from glass substrates to light weight, cost-efficient, and flexible plastic foils and metal sheets. Flexible solar cell would be well suited for industrial-scale mass production, for example with roll-to-roll methods and when integrated on building materials it could work as a functional coating, enabling electricity-producing roofing or façade structures. In the course of this thesis, DSCs were prepared on ITO-PET and ITO-PEN plastics, stainless steel (StS), and optical fibers. Due to the low temperature tolerance of the plastics, development and characterization of room temperature processable counter electrode materials suitable for these substrates was a part of this work. Powder suspension based on carbon nanoparticles proved to be an easily depositable, cost-efficient material with catalytic activity as high as that of platinum. With metal materials, the main problem is the corrosive, iodine-based electrolyte conventionally used in the DSC. This is why, in the beginning of this work, the corrosion resistance of some widely used building materials such as zinc-coated carbon steels, copper, and StS was studied with soaking tests in the electrolyte. StS passed the soaking tests and was chosen for further research. StS has also other benefits such as good electrical conductivity and mechanical sturdiness. Substrate-mediated leakage current is also smaller from StS than from glass substrates. With a DSC configuration where the StS sheet worked as the photoelectrode substrate efficiencies comparable to all-glass cells, near 5 %, were obtained so this configuration was chosen also for the cell size upscaling tests. The largest StS photoelectrode cells prepared in the course of this thesis were 6 cm × 6 cm and their efficiencies over 3 % at their best. This is already a promising value considering the ohmic losses bound to happen at the counter electrode, due to the sheet resistance of the counter electrode substrate. To minimize these losses, additional current collector structures were integrated on the counter electrode substrate with inkjet-printing with silver nanoparticle ink. 50 % reduction in the total ohmic losses of the cell was achieved with the current collector structures and 80 % with replacing the photoelectrode glass substrate with the StS sheet. StS-based DSC would seem like a feasible concept even for industrial-scale mass production but special emphasis should be put, in the future research, on the long term stability of the cells and its improvement. Room for improvement still exists in efficiencies also - a research challenge in which for example some recently developed carbon nanomaterials might provide progress.
Supervising professor
Lund, Peter, Prof.
Thesis advisor
Lund, Peter, Prof.
dye solar cell, plastic substrate, metal substrate, nanomaterials
Other note
  • [Publication 1]: Janne Halme, Minna Toivola, Antti Tolvanen, and Peter Lund. 2006. Charge transfer resistance of spray deposited and compressed counter electrodes for dye-sensitized nanoparticle solar cells on plastic substrates. Solar Energy Materials & Solar Cells, volume 90, numbers 7-8, pages 872-886. © 2005 Elsevier Science. By permission.
  • [Publication 2]: Minna Toivola, Fredrik Ahlskog, and Peter Lund. 2006. Industrial sheet metals for nanocrystalline dye-sensitized solar cell structures. Solar Energy Materials & Solar Cells, volume 90, number 17, pages 2881-2893. © 2006 Elsevier Science. By permission.
  • [Publication 3]: Minna Toivola, Lauri Peltokorpi, Janne Halme, and Peter Lund. 2007. Regenerative effects by temperature variations in dye-sensitized solar cells. Solar Energy Materials & Solar Cells, volume 91, number 18, pages 1733-1742. © 2007 Elsevier Science. By permission.
  • [Publication 4]: Minna Toivola, Janne Halme, Lauri Peltokorpi, and Peter Lund. 2009. Investigation of temperature and aging effects in nanostructured dye solar cells studied by electrochemical impedance spectroscopy. International Journal of Photoenergy, volume 2009, article ID 786429, 15 pages. © 2009 by authors.
  • [Publication 5]: Kati Miettunen, Janne Halme, Minna Toivola, and Peter Lund. 2008. Initial performance of dye solar cells on stainless steel substrates. The Journal of Physical Chemistry C, volume 112, number 10, pages 4011-4017.
  • [Publication 6]: Minna Toivola, Timo Peltola, Kati Miettunen, Janne Halme, and Peter Lund. 2010. Thin film nano solar cells—from device optimization to upscaling. Journal of Nanoscience and Nanotechnology, volume 10, number 2, pages 1078-1084. © 2010 American Scientific Publishers. By permission.
  • [Publication 7]: M. Toivola, K. Miettunen, J. Halme, and P. Lund. 2008. Thin nanostructured solar cells on metal sheets. In: 2008 NSTI Nanotechnology Conference and Trade Show (Nanotech 2008). Boston, USA. 1-5 June 2008. Technical Proceedings of the 2008 CTSI Clean Technology and Sustainable Industries Conference and Trade Show, pages 96-99.
  • [Publication 8]: Minna Toivola, Marju Ferenets, Peter Lund, and Ali Harlin. 2009. Photovoltaic fiber. Thin Solid Films, volume 517, number 8, pages 2799-2802. © 2008 Elsevier Science. By permission.