Nanoplatelet Superlattices by Tin‐Induced Transformation of FAPbI3 Nanocrystals

Abstract The transition from 3D to 2D lead halide perovskites is traditionally led by the lattice incorporation of bulky organic cations. However, the transformation into a coveted 2D superlattice‐like structure by cationic substitution at the Pb 2+ site of 3D perovskite is unfamiliar. It is demonstrated that the gradual increment of Sn 2+ alters the FASn x Pb 1− x I 3 nanocrystals into the Ruddlesden–Popper‐like nanoplatelets (NPLs), with surface‐absorbed oleic acid (OA) and oleylamine (OAm) spacer ligand at 80 °C (FA + : formamidinium cation). These NPLs are stacked either by a perfect alignment to form the superlattice or by offsetting the NPL edges because of their lateral displacements. The phase transition occurs from the Sn/Pb ratio ≥0.011, with 0.64 wt% of Sn 2+ species. At and above Sn/Pb = 0.022, the NPL superlattice stacks start to grow along 00l with a repeating length of 4.37(3) nm, comprising the organic bilayer and the inorganic block having two octahedral layers ( n = 2). Besides, a photoluminescence quantum yield of 98.4% is obtained with Sn/Pb = 0.011 ( n ≥ 4), after surface passivation by trioctylphosphine (TOP).