Bandgap-Engineered Iron Oxides for Solar Energy Harvesting

Epitaxial films of Rh-substituted α-Fe 2 O 3 were fabricated by a pulsed laser deposition technique, and their photoelectrochemical characteristics were investigated for the development of visible light-responsive photoanodes for water splitting. The photocurrent in the films upon irradiation in the visible region was significantly enhanced after Rh substitution. Moreover, a near-infrared photocurrent was clearly observed for Rh:Fe 2 O 3 photoanodes, whereas no photoresponse could be detected for the α-Fe 2 O 3 films. These improved photoelectrochemical properties are attributed to the increased light absorp- tion due to the hybridization of Rh-4 d states and O-2 p states at the valence band maximum. Moreover, Rh substitution also strongly influences the photocarrier transport properties of the films. The electrical conductivity of Rh:Fe 2 O 3 is higher than that for α-Fe 2 O 3 by two orders of magnitude, which is possibly due to the extended 4 d orbitals of the Rh 3+ ions. Thus, the improved electrical properties may lead to an increased photocurrent by lowering the recombination rate of photogenerated carriers.