Fig. 7. Intercalation/deintercalation in R-PEA₂PbI₄ materials. (A) Diagram showing how organic cation penetration into the perovskite layer can lead to Pb–I–Pb bond distortions and interactions with cation “tail” and adjacent axial halide. (B) Band gap energy calculated from the absorption excitonic peak plotted for various R-groups in R-PEA₂PbI₄ films. (C–E) Results of MA intercalation/deintercalation across three select R-PEA₂PbI₄ materials. From left to right is shown, the structure of the A-site cation, UV-visible absorbance spectra of the R-PEA₂PbI₄ film before and after one switch, and SEM images of film morphology for these materials before and after one switch. Reproduced with permission from ref. 52. Copyright 2022, American Chemical Society.