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

摘要

We report here fast A-site cation cross-exchange between APbX3 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 = CI,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.