We report on the synthesis and characterization of a donor–acceptor ruthenium polypyridyl complex as a photosensitizer for p-type dye-sensitized solar cells (DSSCs). The electrochemical, photophysical, and photovoltaic performance of two ruthenium-based photosensitizers were tested in NiO-based DSSCs; bis-(2,2′-bipyridine-4,4′-dicarboxylic acid)2N-(1,10-phenanthroline)-4-nitronaphthalene-1,8-dicarboximide ruthenium(II), ([Ru(dcb)2(NMI-phen)](PF6)2) and tris-(2,2′-bipyridine-4,4′-dicarboxylic acid)3 ruthenium(II), [(Ru(dcb)3)Cl2]. The presence of an electron-accepting group, 4-nitronaphthalene-1,8-dicarboximide (NMI), attached to the phenanthroline of [Ru(dcb)2(NMI-phen)]2+ resulted in long-lived charge separation between reduced [Ru(dcb)2(NMI-phen)]2+ and NiO valence band holes; 10–50 μs. In the reduced state for [Ru(dcb)2(NMI-phen)]2+, the electron localized on the distal NMI group. In tests with I3−/I− and Co(4,4′-di-tert-butyl-bipyridine)32+/3+ electrolytes, [Ru(dcb)2(NMI-phen)]2+ outperformed [Ru(dcb)3]2+ in solar cell efficiency in devices. A record APCE (25%) was achieved for a ruthenium photosensitizer in a p-type DSSC. Insights on photosensitizer regeneration kinetics are included.
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