Theoretical analysis of an intermediate band in Sn-doped hematite with wide-spectrum solar response

Hematite alpha-Fe2O3 is exposed to be an efficient photocatalytic material for the photoelectrochemical water splitting process under visible light. In the present work, we have improved the photocatalytic activity of hematite by varying tin concentration substituted for Fe in pristine hematite. To investigate the influence of the contents of Sn on the photocatalytic activity, various key properties like electronic structure and optoelectronic properties were studied based on density functional theory using generalized gradient approximation plus on-site Hubbard interaction within the WIEN2k computer program. The results of the electronic band structure show the insulating character of the pristine hematite exhibits a bandgap of 2.17 eV equals to Exp. one. The electronic structure calculations of the Sn-doped hematite explore the engineering of the orbitals around the Fermi level and result in a reduction in the bandgap, which is attributed to the corresponding Sn contents. The doping of Sn in Fe2O3 would introduce sub-bands (intermediate band) in between the valence band maximum (VBM) and Fermi level E-F, and more interestingly, half-filled intermediate bands appear around the Fermi level with the increase of Sn contents. To see the effect of intermediate bands on the optoelectronic features of the Sn-doped hematite, we also calculated the optical properties of pristine and doped hematite, which predict extra peaks assigned to transitions of electrons from intermediate bands in the infrared region. Our findings explore that the presence of intermediate bands facilitates the PEC activity of water splitting of Fe2O3, shifting from visible light to infrared region. Here, we demonstrate the idea of intermediate bands in hematite for distinctive device applications.