Dye sensitization of natural anatase crystals with a ruthenium-based dye

The sensitization of natural semiconducting anatase crystals from two different locations was investigated using a ruthenium-based dye (cis-di(thiocyanato)-bis(2,2'-bipyridyl-4,4'-dicarboxylate)ruthenium(II), also known as N3). A maximum incident-photon to sensitized photocurrent conversion efficiency of 3.2 x 10(-4) was measured. The crystal face dependence of the sensitization efficiency was also investigated as well as the adsorption kinetics for N3. The efficiency of sensitization of the (101) face was approximately one order of magnitude higher than for the (001) face. Various surface binding geometries for N3 on the two anatase crystal surfaces are discussed. Sensitization yields that varied by a factor of four were also observed on (101) faces depending on the identity of the crystal. Examination of the morphology of the crystal surfaces with atomic force microscopy and scanning electron microscopy indicated that differences in sensitization efficiency on different faces and crystals were not solely the result of differences in microscopic surface areas. The rise time for sensitized photocurrents decreased with higher light intensities and higher N3 coverages suggesting that trap states, associated with trapping and detrapping of injected electrons, can be saturated. The comparison of the sensitization behavior between anatase single crystals (natural and synthetic! and nanocrystalline anatase films revealed that the absorbed photon-to-current efficiency of the nanocrystalline films is approximately three to seven times greater than on single crystals. (C) 2002 The Electrochemical Society.