Photoelectrochemical cells based on colloidal films of titanium dioxide and zinc oxide ceramic electrodes sensitized by a bis(2,9-diphenyl-1,10-phenanthroline)copper(I) complex modified at the para positions with NaO2C groups, were investigated in an aqueous medium using hydroquinone as electron donor. The sensitizing effect is greater with the films due to the enhanced geometric area projection. The photocurrent-action spectrum obtained with this complex covers almost the whole of the solar visible region. The quantum efficiency was found to depend on the degree of surface coverage by the complex. In a solar-cell arrangement the open-circuit photovoltage was 0.6 V with a small short-circuit photocurrent of ca. 0.6 mA cm-2 in iodide-containing propylene carbonate. © Copyright 1994 by the Royal Society of Chemistry.