Article ID: 20150110
Cs2SnI6, a variant of perovskite CsSnI3, is gaining interest as a photovoltaic material. Based on a simple ionic model, it is expected that Cs2SnI6 is composed of Cs+, I−, and Sn4+ ions and that the band gap is primarily made of occupied I− 5p6 valence band maximum (VBM) and unoccupied Sn4+ 5s conduction band minimum (CBM) similar to SnO2. In this work, we performed density functional theory (DFT) calculations and revealed that the real oxidation state of the Sn ion in Cs2SnI6 is +2 similar to CsSnI3. The +2 oxidation state of Sn originates from 2 ligand holes (L+) in the [SnI6]2− octahedron unit, where the ligand [I6] cluster has the apparent [I66−L+2]4− oxidation state, because the band gap is formed mainly by occupied I 5p VBM and unoccupied I 5p CBM. The +2 oxidation state of Sn and the band gap are originated from the intracluster hybridization and stabilized by the strong covalency of the Sn–I bonds.
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