Diverse CsPbI ₃ assembly structures: the role of surface acids

Surface ligand engineering, seed introduction and external driving forces play major roles in controlling the anisotropic growth of halide perovskites, which have been widely established in CsPbBr₃ nanomaterials. However, colloidal CsPbI₃ nanocrystals (NCs) have been less studied due to their low formation energy and low electronegativity. Here, by introducing different molar ratios of surface acids and amines to limit the monomer concentration of lead-iodine octahedra during nucleation, we report dumbbell-shaped CsPbI₃ NCs obtained by the in situ self-assembly of nanospheres and nanorods with average sizes of 89 nm and 325 nm, respectively, which showed a high photoluminescence quantum yield of 89%. Structural and surface state analyses revealed that the strong binding of benzenesulfonic acid promoted the formation of a Pb(SO₃^-)_x-rich surface of CsPbI₃ assembly structures. Furthermore, the addition of benzenesulfonic acid increases the supersaturation threshold and the solubility of PbI₂ in a high-temperature reaction system, and controls effectively the lead-iodine octahedron monomer concentration in the second nucleation stage. As a result, the as-synthesized CsPbI₃-S_n NCs exhibited different assembly morphologies and high PLQYs, among which the role of sulfonate groups can be further verified by UV absorption and surface characteristics. The strategy provides a new frontier to rationally control the surface ligand-induced self-assembly structures of perovskites.