Fast A-Site Cation Cross-Exchange at Room Temperature: Single-to Double- and Triple-Cation Halide Perovskite Nanocrystals

We report here fast A-site cation cross-exchange between APbX(3) perovskite nanocrystals (NCs) made of different A-cations (Cs (cesium), FA (formamidinium), and MA (methylammonium)) at room temperature. Surprisingly, the A-cation cross-exchange proceeds as fast as the halide (X=Cl, Br, or I) exchange with the help of free A-oleate complexes present in the freshly prepared colloidal perovskite NC solutions. This enabled the preparation of double (MACs, MAFA, CsFA)- and triple (MACsFA)-cation perovskite NCs with an optical band gap that is finely tunable by their A-site composition. The optical spectroscopy together with structural analysis using XRD and atomically resolved high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and integrated differential phase contrast (iDPC) STEM indicates the homogeneous distribution of different cations in the mixed perovskite NC lattice. Unlike halide ions, the A-cations do not phase-segregate under light illumination.

Automated summary

This research reports the fast exchange of A-site cations between perovskite nanocrystals (NCs) made of different A-cations at room temperature. The exchange of A-cations is found to be as fast as the exchange of halide ions. It is shown that the optical properties of perovskite NCs can be finely tuned by the composition of A-cations, and different cations are evenly distributed in the lattice.