Abstract
Evolution of the electronic structure and partial oxidation state of tin and iodine in ASnI3, where A = CH3NH3 (MA), CH(NH2)2 (FA) and Cs, is reported with a view to develop stable, long-term, non-toxic halide-perovskite solar cells.
Highlights
power conversion efficiencies (PCEs) compared to Pb-based perovskites largely due to moisture-induced instability, the presence of deep trap states and degradation.[8,9] Instability in air and moisture is inherent with soluble toxic lead. Tin (Sn), given that it readily oxidises from its Sn2+ oxidation state, which is needed for the formation of stable perovskite octahedra, to its more energetically stable ionic form of Sn4+, resulting in the decomposition of the perovskite lattice
All the [ASnI3]2+ structures result in a reduction in the unit cell volume in comparison to their ASnI3 counterparts, which is due to the removal of two valence electrons, as shown in Table S1 (ESI†)
This volume reduction was observed in the SnI6 octahedra, with little volume change observed in the A site
Summary
PCEs compared to Pb-based perovskites largely due to moisture-induced instability, the presence of deep trap states and degradation.[8,9] Instability in air and moisture is inherent with Sn, given that it readily oxidises from its Sn2+ oxidation state, which is needed for the formation of stable perovskite octahedra, to its more energetically stable ionic form of Sn4+, resulting in the decomposition of the perovskite lattice. All the [ASnI3]2+ structures result in a reduction in the unit cell volume in comparison to their ASnI3 counterparts, which is due to the removal of two valence electrons, as shown in Table S1 (ESI†).
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