Figure 8.

Sn oxidation in THP precursors. a) Images of fresh and aged FASnI₃ solutions in DMSO solvent (left) and in DMF solvent (right). ¹H NMR spectra of FASnI₃ solutions in DMSO solvent b) before and c) after thermal treatment (120°C, 10 min). The peak at 2.07 ppm indicates the presence of DMS. a–c) Reproduced with permission.^{[ 110 ]} Copyright 2020, American Chemical Society. d) Image of Sn oxidation of Sn²⁺ to Sn⁴⁺ in THP solution in ambient air (top), and reduction of Sn⁴⁺ to Sn²⁺ with the addition of metallic Sn powder. e) Schematic representation of Sn vacancy formation due to presence of Sn⁴⁺ in mixed Sn‐Pb perovskite precursor solution (top) and suppression of Sn vacancy formation in Sn‐reduced precursor solution with the absence of Sn⁴⁺. (d,e) Reproduced with permission.^{[ 128 ]} Copyright 2019, Nature Publishing Group.