Photoelectrochemical impedance spectroscopy of electrodeposited hematite α-Fe2O3 thin films: effect of cycle numbers

Abstract

In this work, hematite (α-Fe2O3) onto (FTO)-coated glass substrates have been prepared by electrodeposition technique using cyclic voltammetry process. Various samples of α-Fe2O3 with cycle numbers varied between 25 and 300 were prepared. XRD analysis shows that all films crystallize in a rhombohedral phase of hematite with a preferential orientation along (104) direction. The variation in intensity of the principal peaks shows that the crystallinity of thin films was influenced by the cycle numbers or thickness. Surface morphology studies by scanning electron microscopy (SEM) showed that an increase in the cycle numbers causes an increase in the grain size and homogenous of the surface. Moreover, the optical analysis reveals that the band gap energy varied between 2.1 and 1.9 eV in terms of cycle numbers increase. On the other hand, the photo-electrochemical impedance spectroscopy (PEIS) data have been modeled using an equivalent circuit approach. Finally, from Mott–Schottky plot, the flat-band potential and carrier density of α-Fe2O3 thin films have been determined. The results reveal that all the films showed n-type semiconductor character with a flat band potential and a carrier density changed with cycle numbers.