Fig. 1. (A and B) Crystal structures of 2D RP perovskites with a formula of S₂PbX₄ (A) and 2D DJ perovskites with a formula of SPbX₄ (B). (C) XRD patterns obtained for 2D mixed halide perovskites of Br : I = 50 : 50 with BA, BzA, BDA, and PDMA as spacers. (D and E) XPS spectra for Pb 4f and I 3d recorded for 2D mixed halide perovskites with BA, BzA, BDA, and PDMA as spacers from bottom to top.