Interfacial insight in multi-junction metal oxide photoanodes for water splitting applications

Photoelectrochemical (PEC) properties of nanostructured hematite (Fe2O3) thin films prepared using plasma -enhanced chemical vapor deposition (PE-CVD) were investigated against the influence of processing parameters and post -synthesis heat -treatment procedures. Annealing at high temperatures (>500 degrees C) was found to substantially affect the micro -structure (grain growth and densification) and electronic (interdiffusion at the film/substrate interface) concomitantly manifested in an enhancement in the PEC behavior. The Sn impurity level in hematite films was found to increase with the annealing temperature with highest values achieved in samples heat -treated at 750 degrees C, due to the interdiffusion and substitution of Sn(IV) species at Fe(III) sites. Sn:Fe2O3 films exhibited significantly high photocurrent density of 1.33 mA cm(-2) at the water oxidation level of 1.23 V vs. RHE. The diffusion of Sn ions into iron oxide lattice altered the electronic properties of hematite films due to electron -donor behavior of the dopants that was verified by X-ray photoelectron spectroscopy and secondary ion mass spectroscopy (SIMS) analyses. Deposition of a thin overlayer of TiO2 (10 nm) on hematite films by atomic layer deposition (ALD) was found to further improve the photocurrent density to 1.8 mA cm(-2) at 1.23 V vs. RHE. Ab-initio calculations on the effect of substitutional Sn(IV) dopants in the Fe2O3 lattice on the electronic structure and the band alignment between