Tuning of oxygen vacancy-induced electrical conductivity in Ti-doped hematite films and its impact on photoelectrochemical water splitting

Titanium (Ti)-doped hematite (alpha -Fe2O3) films were grown in oxygen-depleted condition by using the spray pyrolysis technique. The impact of post-deposition annealing in oxygen-rich condition on both the conductivity and water splitting efficiency was investigated. The X-ray diffraction pattern revealed that the films are of rhombohedral alpha -Fe2O3 structure and dominantly directed along (012). The as-grown films were found to be highly conductive with electrons as the majority charge carriers (n-type), a carrier concentration of 1.09x10(20)cm(-3), and a resistivity of 5.9x10(-2) ohm -cm. The conductivity of the films were reduced upon post-deposition annealing. The origin of the conductivity was attributed firstly to Ti4+ substituting Fe3+ and secondly to the ionized oxygen vacancies (V-O) in the crystal lattice of hematite. Upon annealing the samples in oxygen-rich condition, V-O slowly depleted and the conductivity reduced. The photocurrent of the as-grown samples was found to be 3.4mA/cm(-2) at 1.23V vs. RHE. The solar-to-hydrogen efficiency for the as-grown sample was calculated to be 4.18% at 1.23V vs. RHE. The photocurrents were found to be significantly stable in aqueous environment. A linear relationship between conductivity and water-splitting efficiency was established.