Comparative study of photo-excited charge carrier dynamics of atomic layer deposited and solution-derived hematite films: Dependence of charge carrier kinetics on surface orientations

[Display omitted] •Electron/hole recombination in atomic layer deposited hematite was slower than that in solution-derived hematite.•Trapping of the long-lived holes to the surface state in the solution-derived hematite was observed at faster time region than that in atomic layer deposited hematite.•Diffusion of the holes in atomic layer deposited hematite was slower than that in solution-derived hematite due to the different thickness of the space charge layer. Charge carrier kinetics of hematite films prepared via atomic layer deposition and solution-derived methods were investigated using heterodyne transient grating technique in aqueous solution, depending on bias voltage, to reveal the effects of surface orientation differences on the charge carrier dynamics. We found that the electron/hole recombination in atomic layer deposited hematite was slower than that in solution-derived hematite, indicating the generated charge carriers in atomic layer deposited hematite can survive longer than that in solution-derived hematite, which is usually beneficial for water oxidation. On the other hand, the trapping dynamics of the long-lived holes to the surface state for water photo-oxidation in the solution-derived hematite was observed at faster time region than that in atomic layer deposited hematite, implying that the diffusion of the holes in atomic layer deposited hematite was slower than that in solution-derived hematite due to the different barrier height and width of the space charge layer which strongly depends on the surface orientations. It means that the low charge carrier mobility rather than the retardation of the charge recombination in the atomic layer deposited hematite is a dominant factor in its low photoelectrochemical performance.