Photoelectrochemical sensitisation of ZnO-tetrasulfophthalocyaninatozinc composites prepared by electrochemical self-assembly

Electrodes prepared by a one-step electrochemical synthesis of a dye-loaded ZnO thin film from an aqueous mixture of zinc nitrate and a water soluble phthalocyanine, 2,9,16,23-tetrasulfophthalocyaninatozinc(II) (TSPcZn) have been studied. Homogeneously blue transparent particulate thin films were fo rmed. Monomeric or aggregated TSPcZn species could be obtained dependent on the deposition conditions. Visible light absorbed in TSPcZn led to sensiti sation of ZnO. Negative shifts of the rest potential and anodic photocurren ts were obtained in contact with an iodide-containing electrolyte in accord ance with the n-type conduction of ZnO. Time-resolved measurements indicate d charging and discharging of surface states, allowing discussion of the al ignment of energy levels in the contact as well as of charge transfer and r ecombination in the cases of monomeric or aggregated TSPcZn. Electrons were injected into ZnO from the first excited singlet state of TSPcZn. Monomeri c TSPcZn showed a considerably larger quantum efficiency in sensitisation o f ZnO, whereas a larger rate of charge transfer to the electrolyte was deri ved for the aggregated form. (C) 2000 Elsevier Science S.A. All rights rese rved.