Tuning of oxygen vacancy-induced electrical conductivity in Ti-doped hematite films and its impact on photoelectrochemical water splitting
P. Biswas, Ardak Ainabаyev, Ainur Zhussupbekova, Feljin Jose, Robert O’Connor, Aitkazy Kaisha, Brian Walls, I. V. Shvets
Abstract
Abstract Titanium (Ti)-doped hematite (α-Fe 2 O 3 ) 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 α-Fe 2 O 3 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 1.09×10 20 cm −3 , and a resistivity of 5.9×10 −2 Ω-cm. The conductivity of the films were reduced upon post-deposition annealing. The origin of the conductivity was attributed firstly to Ti 4+ substituting Fe 3+ 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 3.4 mA/cm −2 at 1.23 V vs. RHE. The solar-to-hydrogen efficiency for the as-grown sample was calculated to be 4.18% at 1.23 V vs. RHE. The photocurrents were found to be significantly stable in aqueous environment. A linear relationship between conductivity and water-splitting efficiency was established.