Mixing and Matching Organic Cations in 2D Perovskites

Two-dimensional Ruddlesden-Popper perovskite quantum wells have an incredible degree of synthetic flexibility, as their optoelectronic and physical properties can be tuned by changing the halide or the organic cation spacer molecules. Mixing organic cations is a promising, yet underexplored, way to tune the properties of 2D perovskites. The underlying thermodynamics of whether organic cations will mix or phase separate is not well understood. Here, we investigate organic cation mixing in 2D perovskites and demonstrate that whether cations mix or demix depends on their chemical properties and length. We find that we can tune the phase transition temperature of organic cations in the 2D perovskites by blending alkylammonium cations of different length. We also show that cations with distinctly different chemical properties phase separate and we investigate the nanoscale ordering if these phase-separated perovskite domains using nanoscale infrared imaging with photoinduced force microscopy (PiFM). Our results demonstrate that cation mixing is a powerful way to tune thermodynamic properties of 2D perovskites and template these materials at the nanoscale.