The ruthenium dyes N719, Z907 and C106 with the general structures [RuLL’(NCS)2)] degrade slowly at elevated temperatures (t > 80 ˚C) on the surface of nano-sized TiO2 particles. The degradation takes place by reversible nucleophilic substitution reactions in which one of the thiocyanate ligands is replaced with either the nitrogen additive, e.g. 4-tert-butylpyridine (4-TBP) , or the solvent, e.g. 3-methoxypropionitrile (3-MPN) (eqs. (1)-(3)) [1-3]. In this work, we show that the degradation process of [RuLL´(NCS)2] and the inherent kinetics are highly dependent on the composition of the liquid electrolyte. Various electrolyte compositions with varying concentrations of 4-TBP, Li+ ions and I3- were investigated and their effects on the kinetics of N719-degradation reactions as well as the profile of N719-degradation products were studied. Thermal stability experiments were performed at 100 ºC and are based on simple test-tube experiments carried out in colloidal solutions of N719-loaded TiO2 particles (TiO2|N719). The dye degradation was followed by the use of HPLC-coupled electrospray mass spectrometry and investigations of the formation of complexes between Li+ ions and 4-TBP was analyzed by nuclear magnetic resonance (NMR) spectroscopy. The aim of this work was to better understand the limited thermal stability of RuLL´(NCS)2 dyes in DSC devices prepared with liquid electrolytes so-called “non-robust” electrolytes and to be able to optimize the electrolyte.
Dye-sensitized solar cells
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4th international Conference on Hybrid and Organic Photovoltaics, 2012