26 February 2003 Raman and EIS characterizations of interfacial compounds due to iodides reactions in dye-sensitized solar cells (DSSC)
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Abstract
Raman spectroscopy (RS) was used to study the interfacial species due to the presence of a redox couple in the electrolyte during the operation of dye-sensitized solar cells (DSSC). Two bands appear in the Raman spectra of polypyridinium (ppy) dyes adsorbed on nanocrystalline anatase. They can be directly connected to the presence of iodine/iodide couple because they are not present when hydroquinone/quinone (HQ/Q) redox couple is used. The band at 112 cm-1 has already be assigned to the presence of tri-iodide; it disappears only at very high cathodic polarization. The band at 167 cm-1 is due to the formation of an intermediate compound between the oxidized form of the dye , D+, and iodine; it involves a Py-I bonding. The use of different focusing proves that this compound is located below the adsorbed tri-iodide. Electrochemical Impedance Spectroscopy (EIS) allows to determine the charge transfer kinetics at the three main interfaces of the cell and to characterize the diffusion of tri-iodide species. Three different cell functioning regimes (photocurrent plateau, recombination, accumulation) were described. The Raman intensities of the two iodide-connected bands are investigated in each of the three regimes. The “Py-I” band is strong in the photocurrent plateau range and disappears in the recombination range.
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Marie-Claude Bernard, Hubert Cachet, Polycarpos Falaras, Anne Hugot-Le Goff, N. T. T. Oanh, Thomas Stergiopoulos, "Raman and EIS characterizations of interfacial compounds due to iodides reactions in dye-sensitized solar cells (DSSC)", Proc. SPIE 4801, Organic Photovoltaics III, (26 February 2003); doi: 10.1117/12.452417; https://doi.org/10.1117/12.452417
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