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Carbon Nanomaterials as Counter Electrodes for Dye Solar Cells

Kerttu Aitola

Doctoral dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the School of Science for public examination and debate in Auditorium K216 at the Aalto University School of Science (Espoo, Finland) on the 25th of May 2012 at 12 noon.

Overview in PDF format (ISBN 978-952-60-4628-0)   [3086 KB]
Dissertation is also available in print (ISBN 978-952-60-4627-3)

Abstract

The dye solar cell (DSC) is an interesting emerging technology for photovoltaic conversion of solar electromagnetic energy to electrical energy. The DSC is based mainly on cheap starting materials and it can be manufactured by roll-to-roll deposition techniques on flexible substrates, which is considered as one option for cost-effective large-scale solar cell production.

The most expensive component of the DSC is the transparent conductive oxide glass substrate, and considerable cost reductions can be achieved by changing it to e.g. a plastic substrate. Plastic substrates are very flexible, lightweight and transparent. The state of the art DSC catalyst is thermally deposited or sputtered platinum, but platinum is a rare and expensive metal. Carbon, on the other hand, is widely available and some of its nanomaterials conduct electricity and are catalytic toward the DSC counter electrode (CE) reduction reaction.

In this work, carbon nanomaterials and their composites were studied as the DSC CE active material. The materials were random network single-walled carbon nanotube (SWCNT) film on glass and plastic substrate, vertically aligned multiwalled carbon nanotube "forest" film on steel and quartz substrate and carbon nanoparticle composite film on indium tin oxide-polyethylene terephthalate (ITO-PET) substrate. After comparison of the materials, the SWCNT network film on PET was chosen as the main CE type of this study, since it offers superior conductivity, transparency and flexibility over the other carbon-based CEs, it is also the thinnest and contains only one active material component. When a 30 % transparent SWCNT network film on PET was tested as a DSC CE, it was found out that such a film is not catalytic and conductive enough for a full 1 sun illumination DSC device, but the film could be suitable for a indoor illumination level application. The catalytic properties of a 10 % transparent SWCNT film were improved by depositing conductive PEDOT polymer on the film, and the DSC with such film as the CE had similar efficiency than the reference DSC with a sputtered Pt on ITO-PET CE. The PEDOT-SWCNT film had superior catalytic perfomance over the studied Pt films.

Thus, it can be concluded that carbon nanotube network films and their composite films are a feasible alternative flexible, roll-to-roll depositable DSC CE material.

This thesis consists of an overview and of the following 5 publications:

  1. K. Aitola, J. Halme, N. Halonen, A. Kaskela, M. Toivola, A. G. Nasibulin, K. Kordás, G. Tóth, E. I. Kauppinen, and P. D. Lund. Comparison of dye solar cell counter electrodes based on different carbon nanostructures. Thin Solid Films, 519, p. 8125-8134, June 2011.
  2. K. Aitola, A. Kaskela, J. Halme, V. Ruiz, A. G. Nasibulin, E. I. Kauppinen, and P. D. Lund. Single-walled carbon nanotube thin-film counter electrodes for indium tin oxide-free plastic dye solar cells. Journal of the Electrochemical Society, 157, p. B1831-B1837, October 2010.
  3. K. Aitola, M. Borghei, A. Kaskela, E. Kemppainen, A. G. Nasibulin, E. I. Kauppinen, P. D. Lund, V. Ruiz, and J. Halme. Flexible metal-free counter electrode for dye solar cells based on conductive polymer and carbon nanotubes. Submitted to Journal of Electroanalytical Chemistry, January 2012.
  4. M. Toivola, J. Halme, K. Miettunen, K. Aitola, and P. Lund. Nanostructured dye solar cells on flexible substrates—Review. International Journal of Energy Research, 33, p. 1145-1160, September 2009.
  5. G. Hashmi, K. Miettunen, T. Peltola, J. Halme, I. Asghar, K. Aitola, M. Toivola, and P. Lund. Review of materials and manufacturing options for large area flexible dye solar cells. Renewable and Sustainable Energy Reviews, 15, p. 3717-3732, October 2011.

Keywords: dye solar cell, counter electrode, carbon, nanomaterial, nanotube, nanoparticle, flexible, plastic

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© 2012 Aalto University

Last update 2012-10-31