Anion Exchange and Lateral Heterostructure Formation in Ferromagnetic PEA 2 Cr(Cl,Br) 4 Two-Dimensional Perovskites

• Published in: Journal of the American Chemical Society 2024-10, Vol.146 (42), p.29159-29168
• Main Authors: Walsh, Kelly M, Smith, Rachel T, Gamelin, Daniel R
• Format: Article
• Language: English
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/jacs.4c11490

Postsynthetic vapor-phase anion exchange in the ferromagnetic two-dimensional (2D) hybrid metal-halide perovskite, PEA CrCl (PEA = phenethylammonium), is reported. Anion exchange using vaporous trimethylsilyl bromide (TMS-Br) is shown to drive complete conversion of solution-processed PEA CrCl polycrystalline thin films to PEA CrBr . Low-temperature magnetic circular dichroism spectroscopy indicates ferromagnetic ordering in these PEA CrCl and PEA CrBr films. Via partial anion exchange of exfoliated flakes of PEA CrCl single crystals, we demonstrate that it is possible to generate abrupt lateral PEA CrCl /PEA CrBr magneto-heterointerfaces. Kinetic studies reveal that lateral heterostructure formation is dictated by rapid edge-site halide exchange followed by slower intralayer bromide diffusion, and there is negligible interlayer (3D) bromide or TMS-Br diffusion. The importance of the bulky PEA interlayer cation in suppressing 3D diffusion is highlighted by parallel anion-exchange experiments on MA CrCl (MA = methylammonium), which instead show 3D exchange. Comparison of anion-exchange reactions in PEA CrCl , PEA MnCl , and PEA PbCl shows that 2D bromide diffusion is slowest in PEA CrCl , attributed to the antiferrodistortive ordering found in this composition. In addition to demonstrating both postsynthetic composition control and heterostructure formation in ferromagnetic Cr-based 2D perovskites for the first time, these results also advance our fundamental understanding of ion-exchange processes in this relatively unexplored family of 2D perovskites, broadening opportunities for investigation and control of novel spin effects in low-dimensional metal-halide perovskites.