Alternative Self-Assembled Films of Metal-Ion-Bridged 3,4,9,10-Perylenetetracarboxylic Acid on Nanostructured TiO2 Electrodes and Their Photoelectrochemical Properties

A 3,4,9,10-perylenetetracarboxylic acid (PTA) sensitized nanocystalline TiO2 electrode (P) and three alternative metal-ion-bridged self-assembled films of PTA on nanocrystalline TiO2 electrodes (PMP, M = Ru3+, Fe2+, or Fe3+) were fabricated. While the PTA sensitized TiO2 electrode generated 26.9% of monochromatic incident photon-to-electron conversion efficiency (IPCE) at 480 nm and 4.14 mA cm-2 of a short-circuit photocurrent under an illumination of 94.6 mW cm-2 simulated solar light from a xenon lamp, PMP electrode containing Ru3+ produced 87.0% of IPCE at 480 nm and 8.91 mA cm-2 of a short-circuit photocurrent under the same conditions. On the other hand, charge-transfer efficiencies for PMP electrodes containing Fe2+ or Fe3+ ion were even lower than that for electrode P. The notable change from electrode P to electrode PMP in photoelectric response can be explained by the fact that HOMO energy levels for PMP electrodes are different from that for electrode P. For the first time, the fabrication of self-assembled films of metal-ion-bridged bilayer PTA on a nanostructured TiO2 surface and the corresponding photoelectrochemical properties are reported.