A series of ruthenium complex dyes with different number and position of carboxyl groups on bipyridine ligands, such as Ru(4-carboxyl-4'-methyl-2,2'-bipyridine)(4,4'-dimethyl-2,2'- bipyridine)(NCS)(2) (denoted as RulA), Ru(4-carboxyl-4'-methyl-2,2'-bipyridine)(2)(NCS)(2) (RullA), Ru(4,4'-dicarboxy1-2,2'-bipyridine)(4,4'dimethy1-2,2'-bipyridine)(NCS)(2) (Ru2A), and Ru(4-carboxy1-4'-methy1-2,2'-bipyridine)(4,4'-dicarboxyl-2,2'bipyridine)(NCS)(2) (Ru3A) were synthesized and compared with Ru(4,4'-dicarboxy1-2,2'-bipyridine)(2) (NCS)(2), commonly known as N3 dye for the adsorption behavior on the TiO2 surface and photovoltaic properties of dye-sensitized solar cells. The experimental results show that the tilt angle of ruthenium dyes on the TiO2 surface which is dependent on the number and position of their carboxyl groups strongly affected the photovoltaic performance. (C) 2013 Elsevier B.V. All rights reserved.