Proceedings of 6th International Conference on Hybrid and Organic Photovoltaics (HOPV14)
Publication date: 1st March 2014
Aging and degradation of chemical species are crucial issues for the reliability of the Dye Sensitized Solar Cell (DSCs). In real working condition, series connected cells of a module could suffer strong degradations when shadowing phenomena induce Reverse Bias (RB) regime. In RB a strong chemical modifications of both dye and electrolyte solution has been observed.1
In this work we have analyzed the RB regime by an accelerating procedure where a fixed current of about 120 mA (three times the short circuit current at 1 Sun solar irradiation) is imposed to the cell.2,3
Largely before device’s breakdown we observe a gradual and visually evident cluster shaped browning of platinised counter-electrode in contact with electrolyte solution.
Raman spectroscopy confirms that the observed cluster-shaped browning on counter-electrode is due to aggregations of polyiodide ions on poor catalytic micro-sized platinum particles, and reveals an arose marked fluorescence background, stemming from new chemical species induced by RB stress test.
Fluorescence measurements on RB stressed solutions, each containing a single electrolyte component in 3-methoxypropionionitrile (MPN), reveal that photoluminescence emission is mainly related to degradation mechanisms involving redox couple I-/I3-.
In fact, due to the RB stress, the redox couple unbalanced and the formation of various associated structures between 1-methyl-3-propylimidazolium iodide (PMII) ions is favoured.4 This can be detected by observing the Red Edge Effect (REE) in fluorescence emission spectra of stressed solutions.
Thus, polyiodide formation in RB stressed DSCs could be added to the several depletion channels of triiodide anions and should be taken into account in designing new stable and efficient electrolytes.
Optical image (a) and fluorescence microscopy images of the same device's area, including both active and electrolyte monitor areas, respectively with (b) and without the RB applied stress (c).
[1]Agresti, A.; Pescetelli, S.; Quatela, A.; Mastroianni, S.; Brown, T.M.; Reale, A.; Bignozzi, C.A.; Caramori, S.; Di Carlo, A. Micro-Raman Analysis of Reverse Bias stressed Dye-Sensitized Solar Cells. submitted to RSC Advances 2014. [2]Quatela, A.; Agresti, A.; Mastroianni, S.; Pescetelli, S.; Brown, T. M.; Reale, A.; Di Carlo, A. Fabrication and reliability of dye solar cells: A Resonance Raman scattering study. Microelectronic Reliability 2012, 52, 2487-2489. [3]Mastroianni, S.; Lembo, A.; Brown, T.M.; Reale, A.; Di Carlo, A. Electrochemistry in reverse biased dye solar cells and dye/electrolyte degradation mechanisms. Chemphyschem 2012, 13, 2964–2975. [4]Mandal, P. K.; Paul, A.; Samanta, A. Excitation wavelength dependent fluorescence behavior of the room temperature ionic liquids and dissolved dipolar solutes. Journal of Photochemistry and Photobiology A: Chemistry 2006, 182, 113–120.
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