Impact of fluorine and chlorine doping on the structural, electronic and optical properties of SnO2 : First-principles study

In this work, we carried out in depth the structural, electronic and optical properties of intrinsic, fluorine (F) and chlorine (Cl) doped SnO2, using a pseudo-potential plane-wave scheme in the framework of the density functional theory. We found that the substitution of oxygen by F or Cl elements slightly modified the crystalline parameters without altering the stability of SnO2 compounds. The doping of tin oxide by these two halogens is confirmed by the displacement of the Fermi level position to the conduction band. Consequently, the doped materials are strongly degenerate as illustrated by the Moss-Burstein shift: 2.310 eV and 2.332 eV for F:SnO2 and Cl:SnO2 respectively. On the other hand, the density of states and Mulliken population analysis show that the covalent character of Sn-O bond is maintained after doping, while Sn-X (X=F or Cl) formed bond reveals an ionic nature. In terms of optical properties after doping, intrinsic SnO2 exhibits low absorption while the doped ones are transparent in the visible range, making them more efficient in photovoltaic applications. Moreover, in the ultraviolet (UV) scale, pure and doped tin oxide compounds show better absorption, which may be beneficial for use in devices of protection against UV light and UV absorbers or sensors. Finally, the plasma frequencies of 28.22 eV, 29.16 eV and 27.67 eV for pure, F and Cl doped SnO2, respectively, were obtained.