Stability Issues of Dye Solar Cells

Aalto University, P.O. Box 11000, FI-00076 Aalto www.aalto.fi Author Muhammad Imran Asghar Name of the doctoral dissertation Stability Issues of Dye Solar Cells Publisher School of Science Unit Department of Applied Physics Series Aalto University publication series DOCTORAL DISSERTATIONS 53/2012 Field of research New Energy Technologies Manuscript submitted 13 December 2011 Manuscript revised 1 February 2012 Date of the defence 18 May 2012 Language English Monograph Article dissertation (summary + original articles) Abstract The 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.The 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.