Tailoring Molecular Dimensions of Cesium Lead Bromide Perovskites with Varying Compositions of Oleic Acid and Oleylamine

Abstract The evidence on deciphering nucleation and growth of cesium lead halide perovskite crystals, and establishing the phase diagram of cesium lead halide perovskites of different dimensions is still lacking. In this work, a facile method for the synthesis of cesium lead bromide crystals of different molecular level dimensions at room temperature is presented by varying the OA/OAm ratios without changing the proportions of Cs and Pb precursors. Bromide ions are gradually released in the systems through the gamma‐ray radiation chemistry of bromobenzene. As the volume ratios of OA/OAm increase, different products such as CsBr, Cs 4 PbBr 6 (0D), white δ ‐CsPbBr 3 (1D), γ ‐CsPbBr 3 (3D) associated with PbBr 2 sheets, and γ ‐CsPbBr 3 are obtained in order. 1D δ ‐CsPbBr 3 can be transformed into 2D CsPb 2 Br 5 through CsBr stripping in water. The phase diagram established in this work is helpful for understanding the nucleation and growth mechanism of Cs–Pb–Br perovskite crystals of different dimensions. The nucleation of Cs–Pb–Br perovskite crystals is driven by the supersaturation of either CsBr or PbBr 2 caused by varying OA/OAm ratios, i.e., 0D Cs 4 PbBr 6 at the supersaturation of CsBr, while 3D γ ‐CsPbBr 3 at the supersaturation of PbBr 2 . 1D perovskite is the intermediate state between 0D and 3D perovskites.