Crystal Structure of AgBi₂I₇ Thin Films.

Synthesis of cubic-phase AgBi₂I₇ iodobismuthate thin films and fabrication of air-stable Pb-free solar cells using the AgBi₂I₇ absorber 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 ThZr₂H₇ crystal structure with AgBi₂I₇ stoichiometry. 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 AgBiI₄ type. Both the experimental X-ray diffraction pattern and bandgap can be better explained by the AgBiI₄ structure. Additionally, the proposed AgBiI₄ structure, with octahedral bismuth coordination, removes unphysically short Bi-I bonding within the [BiI₈] hexahedra of the ThZr₂I₇ model. Our results provide critical insights for assessing the photovoltaic properties of AgBi₂I₇ iodobismuthate materials.

Duke Scholars

Author David Mitzi Thomas Lord Department of Mechanical Engineering and Materia ...