By deliberately introducing the thermally degraded form of the dye solar cell sensitizer N719 in dye-sensitized solar cells (DSCs) using synthetically prepared N719-TBP ([Ru(L-H)2(NCS)(4-tert-butylpyridine)]−+N(Bu)4), we have investigated the devastating influence of this ligand substitution product (N719-TBP) on the performance parameters of the cells. Two types of dyed solar cells, based on either N719 or N719-TBP, have been characterized employing standard current−voltage (I−V) performance test, UV−vis optical spectroscopy, incident photon to current efficiency (IPCE), and electrochemical impedance spectroscopy (EIS) methods. The performance tests show a drastic efficiency reduction of ∼50% in the N719-TBP containing cells as compared to N719-dyed cells. The lower performance of N719-TBP was caused by lower overall light harvesting efficiency due to ca. 30 nm blue shift in the absorption spectrum of the dye, ca. 50% shorter electron diffusion length due to lower electron recombination resistance, and ca. 14% lower charge separation efficiency, which most likely can be ascribed to decreased dye regeneration efficiency caused by the replacement of one NCS ligand with TBP in the substitution product. The observations made in this study of DSC cells dyed with the substitution product, representing a worst case scenario of cells with 100% degraded dye, are in agreement with the characteristics of N719-dyed solar cells degraded at 85 °C, where the effect of ligand substitution is somewhat less pronounced.

The dye-sensitized solar cell N719 thermal degradation products [Ru(LH) and characterized by electrospray mass spectrometry and NMR spectroscopy. Dyesensitized solar cells (DSCs or DSSCs) prepared with 1 and 2 have efficiencies that are three and two times lower than N719 cells, respectively. Analysis of the UV/Vis and incidentphoton-to-current efficiency (IPCE) spectra indicates that the main reason for the reduced efficiencies is a reduced electron collection efficiency (η coll ). The substituted dyes give rise to lower potentials and currents. When measured at open circuit voltage illumination, the impedance is very different for

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