Fig. 1. (Color online) (a) Schematic diagram of GIWAXS and GISAXS. Reproduced with permission^[2], Copyright 2017, John Wiley & Sons Inc. (b) Schematic diagram of the formation of vertically orientated 2D perovskite. Reproduced with permission ^[5], Copyright 2018, Nature Publishing Group. (c) Gradient strain at different depths in perovskite layer. Reproduced with permission^[9], Copyright 2019, Nature Publishing Group. (d) Time-resolved GIWAXS for precursor films with and without K⁺ during spin-coating. Reproduced with permission^[13], Copyright 2019, Elsevier Inc. (e) Humidity control set-up. (f) Time-dependence for MAPbI₃ (110) peak area and device performance parameters. (e) and (f), reproduced with permission^[15], Copyright 2018, American Chemical Society.