Interplay of thickness and photoelectrochemical properties in nanostructured α-Fe2O3 thin films

Nanostructured Fe2O3 thin films were grown by plasma enhanced-chemical vapor deposition (PE-CVD) from Ar/O2 plasmas for photoelectrochemical (PEC) water splitting applications. Iron oxide coatings were deposited on fluorine-doped tin oxide (FTO) substrates at 300°C under optimized conditions, and subsequently annealed ex-situin air at 650°C. Structural and compositional analyses confirmed the formation of pure alpha-Fe2O3 (hematite), free from other crystalline iron oxide phases. Controlled variations of the deposition time enabled tuning ofthe thickness and nanoaggregate sizesin the resulting deposits and, correspondingly, their current-voltage characteristics. A maximum photocurrent density close to1mA cm-2was achieved at 1.23 V vs. the Reversible Hydrogen Electrode (RHE), without the need of any oxygen evolution catalyst orover/underlayer. The present findingsrevealed the key role played by the engineering of Fe2O3-based nanomaterials, resulting ultimately in a lowered carrier diffusion length, and in an optimal diffusion of tin from FTO into thinner layers. These features offer an amenable opportunity for harvesting radiant energy to trigger water photoelectrolysis and produce clean hydrogenin a carbon-neutral fashion.