Characterization of N,N'-dimethyl-3,4,9,10-perylenetetracarboxylic acid diimide and phthalocyaninatozinc(II) in electrochemical photovoltaic cells

As a direct comparison to all-solid state photovoltaic cells, photoelectrochemical cells consisting of n-type N,N'-dimethyl-3,4,9,10-perylenetetracarboxylic acid diimide (MePTCDI) and p-type phthalocyaninatozinc(II) (PcZn) thin film electrodes vapour-deposited onto ITO have been investigated in aqueous ferri/ferrocyanide, p-benzoquinone/hydroquinone or I3-/I- electrolytes. The ferri/ferrocyanide cell has been studied in more detail, and the results are discussed with regard to the HOMO-, LUMO-and Fermi-energies of the materials used. A setup of the electrodes in a tandem cell could increase the efficiency of the cell due to improved light harvesting. Saturation of the photocurrent with increasing ferri/ferrocyanide electrolyte concentration at single PcZn or MePTCDI electrodes is discussed using a model of reactant adsorption prior to the charge transfer step. In addition, a decrease observed for the open-circuit voltage of the entire cell with increasing ferri/ferrocyanide concentration leads to an optimum concentration of 10(-3) mol dm(-3).