Abstract
We report on the evolution of the electronic structure with partial oxidation state of tin and iodine from ASnI¬3 to model a space charged region¬, where A = CH3NH3(MA), CH(NH2)2 (FA) or Cs, with a view to develop stable long-term non-toxic halide-perovskite solar cells. Although charge cannot be directly removed from specific elements, we show reduction of the charge primarily of SnI3 in a hypothetical [ASnI3]2+ unit cell is calculated due to the valence band edge being dominated by Sn 5s and I 5p anti-bonding states, accompanied by a reduction in unit cell volume in [ASnI3]2+ compared to ASnI3. Band structure calculations show semiconducting behaviour in ASnI3, with metallic behaviour in [ASnII3]2+; a similar behaviour is also found for APbI3 and [APbI3]2+, where the Pb atoms partial charge than Sn. This research al-lows for the analysis of localised charged regions, directing the ultimate long-term electronic stability in perovskite solar absorbers, such as interface recombination and deep trap states.