First principles study on the electronic and optical properties of B-site ordered double perovskite Sr2MMoO6 (M=Mg, Ca, and Zn)

• Double perovskites were studied by DFT+U for photovoltaic application.
• B-site substitution can be used to tuning the band gap of the double perovskites.
• Optical properties of double perovskites were studied with RPA method.

Electronic and optical properties of double perovskite Sr2MMoO6 (M=Mg, Ca, and Zn) were studied using density functional theory. The double perovskites Sr2MgMoO6 and Sr2CaMoO6 exhibited the direct band gap whereas Sr2ZnMoO6 was found to be indirect band gap material. The valence band maxima consisted mainly of oxygen 2p orbitals, whereas the conduction band minima was composed of hybridization between the B-site of Mo 4d and O 2p orbitals. The on-site Coulomb interaction was examined in terms of the influence of the transition metals׳ d orbitals on the electronic properties of the double perovskites. The dielectric functions and the absorption coefficients were studied from the ground electronic states. These results demonstrated that substituting the B-site elements in double perovskites is a potential method to tune the electronic structure for absorbing visible light for applications in inorganic perovskite solar cells.