AbstractThe photoelectrochemical behaviour of Cu(PPh3)2biq+, Cu(biq)2+ and Cu(dmp)2+ has been examined. Here PPh3, biq and dmp denote triphenylphosphine, 2,2'‐biquinoline and 2,9‐dimethyl‐1,10‐phenanthroline, respectively. Thin films of these complexes deposited on a SnO2 electrode generate anodic photocurrents in a photoelectrochemical cell upon irradiation in their metal‐to‐ligand charge‐transfer absorption band. The stability of the photocurrents, however, is low and is due to photochemical decomposition of the dyes. The photoresponse is stabilized and enhanced by the addition of a supersensitizer, hydroquinone, to the electrolyte solution. The suppression of the photochemical decomposition is complete at hydroquinone levels of 10−3 M for each of the three Cu(I) complexes. The photocurrent quantum efficiencies in the presence of hydroquinone in the electrolyte solution have been measured. Peak values of 1%, 4% and 12% were attained for Cu(biq)2+, Cu(dmp)2+ and Cu(PPh3)2biq+, respectively. These quantum efficiencies are correlated with the lifetimes and redox potentials of the excited states of the complexes.