Stability issues of dye solar cells
School of Science | Doctoral thesis (article-based) | Defence date: 2012-05-18
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Aalto University publication series DOCTORAL DISSERTATIONS, 53/2012
AbstractThe thesis discusses dye solar cells (DSCs) which are emerging as a potential candidate for many applications. The goal of the work was to find more stable and higher performing materials for flexible DSCs, improve understanding of the effects on the DSC stability, and to develop experimental methods that give improved resolution of the degradation mechanisms. First an intensive critical literature review was done to highlight the important degradation mechanisms in DSCs. It was concluded that techniques giving chemical information are needed to understand the degradation reactions and their effect on electrical performance. It would be advantageous to have methods that enable monitoring chemical changes in operating DSCs, or periodically over their lifetime during accelerated ageing tests. Here the focus was on new and advanced in-situ methods that allow continuous study of the aging of the cells. In this regard, optical techniques such as Raman spectroscopy, newly introduced image processing method and recently introduced segmented cell method were employed to bridge the link between the chemical changes in the DSCs and the standard PV measurement methods. Here for instance the image processing was demonstrated to study the bleaching of electrolyte under ultraviolet and visible light at 85°C. The results obtained with the image processing method and the standard electrical measurements were in agreement and showed that the bleaching of electrolyte was initiated by TiO2 and slowed down by the presence of the dye. For the roll-to-roll production of DSCs cheap, flexible and stable substrates are required. In this work, a series of metals i.e. StS 304, StS 321, StS 316, StS 316L and Ti were successfully stabilized at the CE of a DSC by using a sputtered Pt catalyst layer that doubled also as a corrosion blocking layer. This work was an important step forward towards stable flexible DSCs. Finally, the degradation due to the manufacturing step related to the electrolyte filling in the DSC was studied. With the help of recently introduced segmented cell method, it was found the nanoporous film of TiO2 was acting as filter for some of the commonly used electrolyte additives i.e. tBP and NMBI. This resulted in spatial performance variation in the DSC which lead to significant losses in the overall performance (here up to 35 % losses in the up-scaling) and thus it has important implications for large area DSCs.
Supervising professorLund, Peter, Prof.
Thesis advisorMiettunen, Kati, D.Sc.
degradation, dye solar cell, image processing, Raman, stability
- [Publication 1]: Muhammad Imran Asghar, Kati Miettunen, Janne Halme, Paula Vahermaa, Minna Toivola, Kerttu Aitola, and Peter Lund. 2010. Review of stability for advanced dye solar cells. Energy & Environmental Science, volume 3, number 4, pages 418-426.
- [Publication 2]: Anders Rand Andersen, Janne Halme, Torben Lund, Muhammad Imran Asghar, Phuong Tuyet Nguyen, Kati Miettunen, Erno Kemppainen, and Ole Albrektsen. 2011. Charge transport and photocurrent generation characteristics in dye solar cells containing thermally degraded N719 dye molecules. The Journal of Physical Chemistry C, volume 115, number 31, pages 15598-15606.
- [Publication 3]: Muhammad Imran Asghar, Kati Miettunen, Simone Mastroianni, Janne Halme, Henri Vahlman, and Peter Lund. 2012. In situ image processing method to investigate performance and stability of dye solar cells. Solar Energy, volume 86, number 1, pages 331-338.
- [Publication 4]: Muhammad Imran Asghar, Kati Miettunen, Simone Mastroianni, Janne Halme, and Peter Lund. 2011. Demonstration of image processing method to investigate performance and stability of dye solar cells. In: Proceedings of the 26th European Photovoltaic Solar Energy Conference and Exhibition (EU PVSEC 2011). Hamburg, Germany. 5-9 September 2011. Munich, Germany. WIP - Renewable Energies. Pages 563-566. ISBN 3-936338-27-2.
- [Publication 5]: Kati Miettunen, Imran Asghar, Xiaoli Ruan, Janne Halme, Tapio Saukkonen, and Peter Lund. 2011. Stabilization of metal counter electrodes for dye solar cells. Journal of Electroanalytical Chemistry, volume 653, numbers 1-2, pages 93-99.
- [Publication 6]: Kati Miettunen, Muhammad Imran Asghar, Janne Halme, and Peter Lund. 2011. Improved performance and stability of flexible dye solar cells. In: Proceedings of the 26th European Photovoltaic Solar Energy Conference and Exhibition (EU PVSEC 2011). Hamburg, Germany. 5-9 September 2011. Munich, Germany. WIP - Renewable Energies. Pages 587-590. ISBN 3-936338-27-2.
- [Publication 7]: Kati Miettunen, Imran Asghar, Simone Mastroianni, Janne Halme, Piers R. F. Barnes, Emma Rikkinen, Brian C. O'Regan, and Peter Lund. 2012. Effect of molecular filtering and electrolyte composition on the spatial variation in performance of dye solar cells. Journal of Electroanalytical Chemistry, volume 664, pages 63-72.