The dye-sensitized solar cell N719 thermal degradation products [Ru(LH)2(NCS)(4-tert-butylpyridine)][N(Bu)4] (1) and [Ru(LH)2(NCS)(1-methylbenzimidazole)][N(Bu)4] (2) were synthesized from [Ru(LH)2(NCS)2][N(Bu)4]2 (N719), (L = 2,2′-bipyridyl-4,4′-dicarboxylic acid) and characterized by electrospray mass spectrometry and NMR spectroscopy. Dye-sensitized 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 incident-photon-to-current efficiency (IPCE) spectra indicates that the main reason for the reduced efficiencies is a reduced electron collection efficiency (ηcoll). The substituted dyes give rise to lower potentials and currents. When measured at open circuit voltage illumination, the impedance is very different for such cells relative to N719 cells. Furthermore, the lifetime (τeff) of the electrons in the TiO2 is reduced by a factor of around ten. The low τeff values may be related to the positive charge on dyes 1 and 2, which results in an enhanced local concentration of I3– near the photoanode and thereby a higher dark current. N719 cells at higher temperature result in slightly lower potentials, and this alone leads to a change in impedance response when measured at open circuit voltage. The same parts of the impedance spectrum are affected (i.e., the interface between the photoanode and the electrolyte is affected in the same way) when we compare data from N719 heated cells and DSCs prepared with 1 or 2 and not thermally treated.
- Dye-sensitized solar cells