Nanocrystalline solar cells sensitized with monocarboxyl or dicarboxyl pyridylquinoline ruthenium(II) complexes

cis-[Ru(Hmcpq)2(NCS)2] (1; Hmcpq=4-carboxy-2-(2′-pyridyl)quinoline) was newly synthesized, and its spectral (absorption, luminescence) and electrochemical properties were compared with those of cis-[Ru(H2dcpq)2(NCS)2] (2; H2dcpq=4-carboxy-2-[2′-(4′-carboxypyridyl)]quinoline). Solar cells based on nanocrystalline TiO2 film sensitized with 1 showed efficient photosensitization over a large portion of the visible and near-IR spectral region. These solar cells generated a large short-circuit photocurrent (12 mA cm−2), produced an open-circuit voltage of 0.53 V, and exhibited a solar energy conversion efficiency of 4.6% under simulated AM 1.5 solar irradiation (100 mW cm−2). The effects of the number of carboxyl groups in 1 and 2 on the binding to nanocrystalline TiO2 and on the photovoltaic performance of the solar cells were investigated.