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Figure 5. (A) Water molecule adsorption on perovskite surfaces. The MA (top) and TEA surfaces (bottom) are terminated with methyl and tetra-ethyl ammonium cations, respectively^[105]. Copyright 2016 Nature Publishing Group. (B) Modeling atomic structures of functionalized perovskite surfaces. Side (top) and top (middle) views, respectively, of the optimized geometries of the (100) surfaces of MA, TMA and TEA samples. Calculated atomic structure (side view) of different (100) surfaces with molecularly adsorbed water (bottom)^[105]. Copyright 2016 Nature Publishing Group. (C) Water absorption ratio of the perovskite crystals under a relative humidity of 90% ± 5% and dark conditions. Samples of more than 5 g were used in all tests for accuracy. Three regions are defined to classify the moisture resistance of all the samples^[105]. Copyright 2016 Nature Publishing Group. (D) Atomic structures of Cs_1-xFA_xPbI₃ (001) surfaces with adsorbed H₂O and C₄H₆O₂ molecules in a unit cell: CsPbI₃ (left); Cs_0.5FA_0.5PbI₃ (middle); and FAPbI₃ (right)^[64]. Copyright 2020 Royal Society of Chemistry. (E) Evolution of normalized absorbance for pristine (green) and chelated (purple, Pb(DDTC)₂) CsPbI₂Br thin films under dark in ambient atmosphere (RH, 15% ± 3%)^[106]. Copyright 2020 Nature Publishing Group.