The photovoltaic performance of several porphyrin-derivatized TiO2 films in regenerative photoelectrochemical cells is reported and compared to that in cells sensitized with a Ru(2,2'-bipyridyl-4,4'-dicarboxylate)2(NCS)2 (N3) dye. The porphyrin sensitizers tetrakis(3',5'-di-tert-butylphenyl)porphyrin, tetrakis(3',5'-di-tert-butylphenyl)porphyrin zinc(II), and tetrakis(4'-carboxyphenyl)porphyrin were studied. Differences in efficiencies of the porphyrin light absorbers are ascribed to poor electronic coupling of the latter two sensitizers to the titania conduction band. Dark currents and I-V curves were measured as a function of incident ligth intensity and I3-/I- electrolyte concentrations for three different film preparations, with and without a coadsorber. Analysis of dark current results with use of a perviously proposed model suggests that the lower efficiencies yielded with P25 TiO2 supports compared to semitransparent electrodes can be explained, in part, by the differneces in the measured back electron transfer. Photoaction spectra closely matched the prophyrin absorption spectra which we argue is more likely than for similar spectra reported previously in P25 films
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