A new efficient photosensitizer for nanocrystalline solar cells: synthesis and characterization of cis-bis(4,7-dicarboxy-1,10-phenanthroline)dithiocyanato ruthenium(II)

Abstract

The complexes [NBu₄]_2n[cis-Ru(H_2 − ndcphen)₂X₂ (n = 0 or 1; H₂dcphen; = 4,7-dicarboxy-1,10-phenanthroline; X = Cl, CN or SCN) were synthesized and spectroscopically characterized as a new class of photosensitizers. The energy levels of the LUMO and HOMO of cis-[Ru(H₂dcphen)₂(NCS)₂] were estimated to be −1.02 and 0.89 V (vs. SCE), respectively, slightly more positive than those of [NBu₄]_2n[cis-Ru(H_2 − ndcbpy)₂(NCS)₂] (n = 0 or 1; H₂dcbpy = 4,4′-dicarboxy-2,2′-bipyridine). A more intense and broader MLCT absorption of [NBu₄]_2n[cis-Ru(H_2 − ndcphen)₂(NCS)₂] (n = 0 or 1) than that of [NBu₄]_2n[cis-Ru(H_2 − ndcbpy)₂(NCS)₂] (n = 0 or 1) was observed in ethanol solution at around 525 nm in the visible region. It is demonstrated that the new complexes act as efficient light harvesting antennae for dye-sensitized solar cells. A [NBu₄]_2n[cis-Ru(Hdcphen)₂(NCS)₂] sensitized nanocrystalline TiO₂ film shows a remarkable solar light to electrical power conversion efficiency of 6.1% at 100 mW cm⁻² of AM 1.5.