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  Friedrich, D.; Valldecabres, L.; Kunst, M.; Moehl, T.; Zakeeruddin, S.M.; Grätzel, M.: Dye Regeneration Dynamics by Electron Donors on Mesoscopic TiO₂ Films. The Journal of Physical Chemistry C 118 (2014), p. 3420-3425

10.1021/jp4113206

Abstract:
The influence of different redox mediators and electrolyte constituents on charge transfer processes in dye-sensitized solar cells (DSC) was studied by contactless transient photoconductance (TPC) measurements. Device subsets without FTO (Fluorine-doped tin oxide) contacts were prepared to increase the reliability and sensitivity of the TPC measurements. Results revealed a decrease of electron decay rate with increasing concentration of the redox couple ([Co(III/II)(bpy)3](PF6)3/2) which was attributed to an improvement of the reduction of the dye cation (dye regeneration). Furthermore, the presence of the electrolyte additives 4-tert-butylpyridine (TBP) and chenodeoxycholic acid was found to decrease the electron decay rate, which was attributed to blocking of interfacial charge recombination. The use of other redox couples (quinone/hydroquinone and ferrocene/ferrocenium) with these electrolyte additives displayed a significant improvement for ferrocene/ferrocenium, while the electron lifetime for quinone/hydroquinone appeared unaffected. Prospects for a further optimization of DSC’s redox couples are discussed.