title: Crystal Structure of AgBi2I7Thin Films.
abstract: Synthesis of cubic-phase AgBi2I7iodobismuthate thin films and fabrication of air-stable Pb-free solar cells using the AgBi2I7absorber have recently been reported. On the basis of X-ray diffraction (XRD) analysis and nominal composition, it was suggested that the synthesized films have a cubic ThZr2H7crystal structure with AgBi2I7stoichiometry. Through careful examination of the proposed structure and computational evaluation of the phase stability and bandgap, we find that the reported "AgBi2I7" films cannot be forming with the ThZr2H7-type structure, but rather more likely adopt an Ag-deficient AgBiI4type. Both the experimental X-ray diffraction pattern and bandgap can be better explained by the AgBiI4structure. Additionally, the proposed AgBiI4structure, with octahedral bismuth coordination, removes unphysically short Bi-I bonding within the [BiI8] hexahedra of the ThZr2I7model. Our results provide critical insights for assessing the photovoltaic properties of AgBi2I7iodobismuthate materials.
authors.affiliation: Department of Physics and Astronomy, and Wright Center for Photovoltaic Innovation and Commercialization, The University of Toledo , Toledo, Ohio 43607, United States.
authors.forename: Zewen
authors.initials: Z
authors.lastname: Xiao
authors.affiliation: Department of Physics and Astronomy, and Wright Center for Photovoltaic Innovation and Commercialization, The University of Toledo , Toledo, Ohio 43607, United States.
authors.forename: Weiwei
authors.initials: W
authors.lastname: Meng
authors.affiliation: Department of Mechanical Engineering and Materials Science, and Department of Chemistry, Duke University , Durham, North Carolina 27708, United States.
authors.forename: David B
authors.initials: DB
authors.lastname: Mitzi
authors.affiliation: Department of Physics and Astronomy, and Wright Center for Photovoltaic Innovation and Commercialization, The University of Toledo , Toledo, Ohio 43607, United States.
authors.forename: Yanfa
authors.initials: Y
authors.lastname: Yan