Dependence of the voltammetric oxidation of the photovoltaic sensitizer [(H-3-tctpy)Ru-II(NCS)(3)](-) on the electrode material, solvent, and isomeric purity

One of the most efficient sensitizers presently available for photoelectroc hemical solar cell applications is a ruthenium dye based on a terpyridine l igand. The voltammetric oxidation of the N,N,N-bonded thiocyanate isomer of [(H-3-tctpy)Ru-II(NCS)(3)](-)(H-3-tctpy = 2,2':6',2 " -terpyridine-4,4',4 " -tricarboxylic acid), which is relevant to the use of the dye in photovol taic cells, has been studied at platinum, gold, and glassy carbon electrode s. In acetonitrile, the metal-based one-electron oxidation process for the N,N,N-bonded isomer exhibits close to chemically reversible behavior under a wide range of voltammetric conditions, although the presence of surface-b ased reactions coupled to the charge transfer process are evident. The elec trochemical quartz crystal microbalance technique revealed that dye materia l is adsorbed onto the electrode surface under open circuit conditions and that additional surface-based oxidation processes occur at potentials more positive than the initial metal-based oxidation process. Oxidative voltamme try in acetone is similar to that in acetonitrile. However, studies on mixt ures containing S-bonded linkage isomers in this solvent show a shift in re versible potential to less positive values and a decrease in the contributi on of the surface-based processes. In dimethylformamide, low temperatures ( T = -55 degreesC) are necessary to observe a reversible one-electron oxidat ion process. Data are compared to those reported with the more commonly use d [(2,2'-bipyridine-4,4'-dicarboxylicacid)(2)Ru(NCS)(2)] sensitizer. (C) 20 01 The Electrochemical Society. All rights reserved.