| Abstract
| - We have synthesized four carboxylated Ru(II) phenanthroline complexes with different numbers ofcarboxyl groups, cis-bis(4,7-dicarboxy-1,10-phenanthroline)dithiocyanato ruthenium(II) (Ru(dcphen)2(NCS)2), cis-bis(4-monocarboxy-1,10-phenanthroline)dithiocyanato ruthenium(II) (Ru(mcphen)2(NCS)2),cis-(4,7-dicarboxy-1,10-phenanthroline)(1,10-phenanthroline)dithiocyanato ruthenium(II) (Ru(dcphen)(phen)(NCS)2), and cis-(4-monocarboxy-1,10-phenanthroline)(1,10-phenanthroline)dithiocyanato ruthenium(II) (Ru(mcphen)(phen)(NCS)2), as photosensitizers for oxide semiconductor solar cells. We havestudied photovoltaic properties of dye-sensitized nanocrystalline semiconductor solar cells based on Ruphenanthroline complexes and an iodine redox electrolyte. The photovoltaic performance of the TiO2 solarcell sensitized by Ru(dcphen)2(NCS)2(TBA)2 exceeded that of ZnO, SnO2, and In2O3 solar cells. A solarenergy to electricity conversion efficiency (η) of 6.6% was obtained under the standard AM 1.5 irradiation(100 mW cm-2, JIS A class) with a short-circuit photocurrent density (Jsc) of 12.5 mA cm-2, an open-circuitphotovoltage (Voc) of 0.74 V, and a fill factor (ff) of 0.71. Monochromatic incident photon to current conversionefficiency was 78% at 526 nm. Deoxycholic acid as a coadsorbate and decreasing film thickness improvedVoc especially due to suppression of the dark current reaction corresponding to the reduction of triiodideions with injected electrons. The improved photovoltaic property due to the added coadsorbate suggeststhat some aggregates of the Ru complex suppress efficient electron injection to the semiconductor. Theposition and number of carboxyl groups attached to the phenanthroline ligand as an anchor affectphotosensitizer performance significantly, suggesting that the anchoring configuration of Ru phenanthrolinecomplexes on the semiconductor surface is important to efficient photovoltaic cell performance. Two carboxylgroups attached to phenanthroline ligands are necessary for effective electron injection.
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