Photocurrent Generation in Heterostructured Ultrathin Films Fabricated by Layer-by-Layer Deposition of Polyelectrolytes Bearing Tris(2,2'-bipyridine)ruthenium(II) and Ferrocene Moieties

摘要

The photoelectrochemical properties of single-component and heterostructured layer-by-layer deposited films bearing tris(2,2'-bipyridine)ruthenium(II) (Ru) moieties were investigated by photocurrent measurements in solutions in the presence of sacrificial reagents.The photocurrent increased with an increase in the thickness of the films and then had a maximum at a thickness of 10 nm.This increase demonstrates a light-harvesting effect based on excitation energy migration among the Ru moieties to the film/electrolyte interface.A cathodic photocurrent was observed for a heterostructured film where bilayers bearing ferrocene (Fc) moieties and bilayers bearing Ru moieties were deposited on an indium tin oxide (ITO) substrate in the order (ITO/Fc/Ru).On the other hand,an anodic photocurrent was observed for the reverse order film (ITO/Ru/Fc).These results show that the direction of the photocurrent is determined by the gradient of the redox potentials formed in the heterostructured films.The internal quantum efficiency for the ITO/ Ru/Fc film was twice that for the single-component film (ITO/Ru).This enhancement of the quantum efficiency is due to suppression of charge recombination by successive electron transfers in the heterostructured film.